— Function: const char * gnutls_alert_get_name (gnutls_alert_description_t alert)

alert: is an alert number gnutls_session_t structure.

This function will return a string that describes the given alert number or NULL. See gnutls_alert_get().

— Function: gnutls_alert_description_t gnutls_alert_get (gnutls_session_t session)

session: is a gnutls_session_t structure.

This function will return the last alert number received. This function should be called if GNUTLS_E_WARNING_ALERT_RECEIVED or GNUTLS_E_FATAL_ALERT_RECEIVED has been returned by a gnutls function. The peer may send alerts if he thinks some things were not right. Check gnutls.h for the available alert descriptions.

If no alert has been received the returned value is undefined.

— Function: int gnutls_alert_send_appropriate (gnutls_session_t session, int err)

session: is a gnutls_session_t structure.

err: is an integer

Sends an alert to the peer depending on the error code returned by a gnutls function. This function will call gnutls_error_to_alert() to determine the appropriate alert to send.

This function may also return GNUTLS_E_AGAIN, or GNUTLS_E_INTERRUPTED.

If the return value is GNUTLS_E_INVALID_REQUEST, then no alert has been sent to the peer.

Returns zero on success.

— Function: int gnutls_alert_send (gnutls_session_t session, gnutls_alert_level_t level, gnutls_alert_description_t desc)

session: is a gnutls_session_t structure.

level: is the level of the alert

desc: is the alert description

This function will send an alert to the peer in order to inform him of something important (eg. his Certificate could not be verified). If the alert level is Fatal then the peer is expected to close the connection, otherwise he may ignore the alert and continue.

The error code of the underlying record send function will be returned, so you may also receive GNUTLS_E_INTERRUPTED or GNUTLS_E_AGAIN as well.

Returns 0 on success.

— Function: int gnutls_anon_allocate_client_credentials (gnutls_anon_client_credentials_t * sc)

sc: is a pointer to an gnutls_anon_client_credentials_t structure.

This structure is complex enough to manipulate directly thus this helper function is provided in order to allocate it.

Returns a negative value in case of an error.

— Function: int gnutls_anon_allocate_server_credentials (gnutls_anon_server_credentials_t * sc)

sc: is a pointer to an gnutls_anon_server_credentials_t structure.

This structure is complex enough to manipulate directly thus this helper function is provided in order to allocate it.

Returns a negative value in case of an error.

— Function: void gnutls_anon_free_client_credentials (gnutls_anon_client_credentials_t sc)

sc: is an gnutls_anon_client_credentials_t structure.

This structure is complex enough to manipulate directly thus this helper function is provided in order to free (deallocate) it.

— Function: void gnutls_anon_free_server_credentials (gnutls_anon_server_credentials_t sc)

sc: is an gnutls_anon_server_credentials_t structure.

This structure is complex enough to manipulate directly thus this helper function is provided in order to free (deallocate) it.

— Function: void gnutls_anon_set_params_function (gnutls_anon_server_credentials_t res, gnutls_params_function * func)

res: is a gnutls_anon_server_credentials_t structure

func: is the function to be called

This function will set a callback in order for the server to get the diffie hellman or RSA parameters for anonymous authentication. The callback should return zero on success.

— Function: void gnutls_anon_set_server_dh_params (gnutls_anon_server_credentials_t res, gnutls_dh_params_t dh_params)

res: is a gnutls_anon_server_credentials_t structure

dh_params: is a structure that holds diffie hellman parameters.

This function will set the diffie hellman parameters for an anonymous server to use. These parameters will be used in Anonymous Diffie Hellman cipher suites.

— Function: void gnutls_anon_set_server_params_function (gnutls_anon_server_credentials_t res, gnutls_params_function * func)

res: is a gnutls_certificate_credentials_t structure

func: is the function to be called

This function will set a callback in order for the server to get the diffie hellman parameters for anonymous authentication. The callback should return zero on success.

— Function: gnutls_credentials_type_t gnutls_auth_client_get_type (gnutls_session_t session)

session: is a gnutls_session_t structure.

Returns the type of credentials that were used for client authentication. The returned information is to be used to distinguish the function used to access authentication data.

— Function: gnutls_credentials_type_t gnutls_auth_get_type (gnutls_session_t session)

session: is a gnutls_session_t structure.

Returns type of credentials for the current authentication schema. The returned information is to be used to distinguish the function used to access authentication data.

Eg. for CERTIFICATE ciphersuites (key exchange algorithms: KX_RSA, KX_DHE_RSA), the same function are to be used to access the authentication data.

— Function: gnutls_credentials_type_t gnutls_auth_server_get_type (gnutls_session_t session)

session: is a gnutls_session_t structure.

Returns the type of credentials that were used for server authentication. The returned information is to be used to distinguish the function used to access authentication data.

— Function: int gnutls_bye (gnutls_session_t session, gnutls_close_request_t how)

session: is a gnutls_session_t structure.

how: is an integer

Terminates the current TLS/SSL connection. The connection should have been initiated using gnutls_handshake(). how should be one of GNUTLS_SHUT_RDWR, GNUTLS_SHUT_WR.

In case of GNUTLS_SHUT_RDWR then the TLS connection gets terminated and further receives and sends will be disallowed. If the return value is zero you may continue using the connection. GNUTLS_SHUT_RDWR actually sends an alert containing a close request and waits for the peer to reply with the same message.

In case of GNUTLS_SHUT_WR then the TLS connection gets terminated and further sends will be disallowed. In order to reuse the connection you should wait for an EOF from the peer. GNUTLS_SHUT_WR sends an alert containing a close request.

Note that not all implementations will properly terminate a TLS connection. Some of them, usually for performance reasons, will terminate only the underlying transport layer, thus causing a transmission error to the peer. This error cannot be distinguished from a malicious party prematurely terminating the session, thus this behavior is not recommended.

This function may also return GNUTLS_E_AGAIN or GNUTLS_E_INTERRUPTED; cf. gnutls_record_get_direction().

— Function: time_t gnutls_certificate_activation_time_peers (gnutls_session_t session)

session: is a gnutls session

This function will return the peer's certificate activation time. This is the creation time for openpgp keys.

Returns (time_t) -1 on error.

— Function: int gnutls_certificate_allocate_credentials (gnutls_certificate_credentials_t * res)

res: is a pointer to an gnutls_certificate_credentials_t structure.

This structure is complex enough to manipulate directly thus this helper function is provided in order to allocate it.

Returns 0 on success.

— Function: int gnutls_certificate_client_get_request_status (gnutls_session_t session)

session: is a gnutls session

This function will return 0 if the peer (server) did not request client authentication or 1 otherwise. Returns a negative value in case of an error.

— Function: void gnutls_certificate_client_set_retrieve_function (gnutls_certificate_credentials_t cred, gnutls_certificate_client_retrieve_function * func)

cred: is a gnutls_certificate_credentials_t structure.

func: is the callback function

This function sets a callback to be called in order to retrieve the certificate to be used in the handshake. The callback's function prototype is: int (*callback)(gnutls_session_t, const gnutls_datum_t* req_ca_dn, int nreqs, gnutls_pk_algorithm_t* pk_algos, int pk_algos_length, gnutls_retr_st* st);

st should contain the certificates and private keys.

req_ca_cert, is only used in X.509 certificates. Contains a list with the CA names that the server considers trusted. Normally we should send a certificate that is signed by one of these CAs. These names are DER encoded. To get a more meaningful value use the function gnutls_x509_rdn_get().

pk_algos, contains a list with server's acceptable signature algorithms. The certificate returned should support the server's given algorithms.

If the callback function is provided then gnutls will call it, in the handshake, after the certificate request message has been received.

The callback function should set the certificate list to be sent, and return 0 on success. If no certificate was selected then the number of certificates should be set to zero. The value (-1) indicates error and the handshake will be terminated.

— Function: time_t gnutls_certificate_expiration_time_peers (gnutls_session_t session)

session: is a gnutls session

This function will return the peer's certificate expiration time.

Returns (time_t) -1 on error.

— Function: void gnutls_certificate_free_ca_names (gnutls_certificate_credentials_t sc)

sc: is an gnutls_certificate_credentials_t structure.

This function will delete all the CA name in the given credentials. Clients may call this to save some memory since in client side the CA names are not used.

CA names are used by servers to advertize the CAs they support to clients.

— Function: void gnutls_certificate_free_cas (gnutls_certificate_credentials_t sc)

sc: is an gnutls_certificate_credentials_t structure.

This function will delete all the CAs associated with the given credentials. Servers that do not use gnutls_certificate_verify_peers2() may call this to save some memory.

— Function: void gnutls_certificate_free_credentials (gnutls_certificate_credentials_t sc)

sc: is an gnutls_certificate_credentials_t structure.

This structure is complex enough to manipulate directly thus this helper function is provided in order to free (deallocate) it.

This function does not free any temporary parameters associated with this structure (ie RSA and DH parameters are not freed by this function).

— Function: void gnutls_certificate_free_crls (gnutls_certificate_credentials_t sc)

sc: is an gnutls_certificate_credentials_t structure.

This function will delete all the CRLs associated with the given credentials.

— Function: void gnutls_certificate_free_keys (gnutls_certificate_credentials_t sc)

sc: is an gnutls_certificate_credentials_t structure.

This function will delete all the keys and the certificates associated with the given credentials. This function must not be called when a TLS negotiation that uses the credentials is in progress.

— Function: const gnutls_datum_t * gnutls_certificate_get_ours (gnutls_session_t session)

session: is a gnutls session

This function will return the certificate as sent to the peer, in the last handshake. These certificates are in raw format. In X.509 this is a certificate list. In OpenPGP this is a single certificate. Returns NULL in case of an error, or if no certificate was used.

— Function: const gnutls_datum_t * gnutls_certificate_get_peers (gnutls_session_t session, unsigned int * list_size)

session: is a gnutls session

list_size: is the length of the certificate list

This function will return the peer's raw certificate (chain) as sent by the peer. These certificates are in raw format (DER encoded for X.509). In case of a X.509 then a certificate list may be present. The first certificate in the list is the peer's certificate, following the issuer's certificate, then the issuer's issuer etc.

In case of OpenPGP keys a single key will be returned in raw format.

Returns NULL in case of an error, or if no certificate was sent.

— Function: void gnutls_certificate_send_x509_rdn_sequence (gnutls_session_t session, int status)

session: is a pointer to a gnutls_session_t structure.

status: is 0 or 1

If status is non zero, this function will order gnutls not to send the rdnSequence in the certificate request message. That is the server will not advertize it's trusted CAs to the peer. If status is zero then the default behaviour will take effect, which is to advertize the server's trusted CAs.

This function has no effect in clients, and in authentication methods other than certificate with X.509 certificates.

— Function: void gnutls_certificate_server_set_request (gnutls_session_t session, gnutls_certificate_request_t req)

session: is an gnutls_session_t structure.

req: is one of GNUTLS_CERT_REQUEST, GNUTLS_CERT_REQUIRE

This function specifies if we (in case of a server) are going to send a certificate request message to the client. If req is GNUTLS_CERT_REQUIRE then the server will return an error if the peer does not provide a certificate. If you do not call this function then the client will not be asked to send a certificate.

— Function: void gnutls_certificate_server_set_retrieve_function (gnutls_certificate_credentials_t cred, gnutls_certificate_server_retrieve_function * func)

cred: is a gnutls_certificate_credentials_t structure.

func: is the callback function

This function sets a callback to be called in order to retrieve the certificate to be used in the handshake. The callback's function prototype is: int (*callback)(gnutls_session_t, gnutls_retr_st* st);

st should contain the certificates and private keys.

If the callback function is provided then gnutls will call it, in the handshake, after the certificate request message has been received.

The callback function should set the certificate list to be sent, and return 0 on success. The value (-1) indicates error and the handshake will be terminated.

— Function: void gnutls_certificate_set_dh_params (gnutls_certificate_credentials_t res, gnutls_dh_params_t dh_params)

res: is a gnutls_certificate_credentials_t structure

dh_params: is a structure that holds diffie hellman parameters.

This function will set the diffie hellman parameters for a certificate server to use. These parameters will be used in Ephemeral Diffie Hellman cipher suites. Note that only a pointer to the parameters are stored in the certificate handle, so if you deallocate the parameters before the certificate is deallocated, you must change the parameters stored in the certificate first.

— Function: void gnutls_certificate_set_params_function (gnutls_certificate_credentials_t res, gnutls_params_function * func)

res: is a gnutls_certificate_credentials_t structure

func: is the function to be called

This function will set a callback in order for the server to get the diffie hellman or RSA parameters for certificate authentication. The callback should return zero on success.

— Function: void gnutls_certificate_set_rsa_export_params (gnutls_certificate_credentials_t res, gnutls_rsa_params_t rsa_params)

res: is a gnutls_certificate_credentials_t structure

rsa_params: is a structure that holds temporary RSA parameters.

This function will set the temporary RSA parameters for a certificate server to use. These parameters will be used in RSA-EXPORT cipher suites.

— Function: void gnutls_certificate_set_verify_flags (gnutls_certificate_credentials_t res, unsigned int flags)

res: is a gnutls_certificate_credentials_t structure

flags: are the flags

This function will set the flags to be used at verification of the certificates. Flags must be OR of the gnutls_certificate_verify_flags enumerations.

— Function: void gnutls_certificate_set_verify_limits (gnutls_certificate_credentials_t res, unsigned int max_bits, unsigned int max_depth)

res: is a gnutls_certificate_credentials structure

max_bits: is the number of bits of an acceptable certificate (default 8200)

max_depth: is maximum depth of the verification of a certificate chain (default 5)

This function will set some upper limits for the default verification function, gnutls_certificate_verify_peers2(), to avoid denial of service attacks.

— Function: int gnutls_certificate_set_x509_crl_file (gnutls_certificate_credentials_t res, const char * crlfile, gnutls_x509_crt_fmt_t type)

res: is an gnutls_certificate_credentials_t structure.

crlfile: is a file containing the list of verified CRLs (DER or PEM list)

type: is PEM or DER

This function adds the trusted CRLs in order to verify client or server certificates. In case of a client this is not required to be called if the certificates are not verified using gnutls_certificate_verify_peers2(). This function may be called multiple times.

Returns the number of CRLs processed or a negative value on error.

— Function: int gnutls_certificate_set_x509_crl_mem (gnutls_certificate_credentials_t res, const gnutls_datum_t * CRL, gnutls_x509_crt_fmt_t type)

res: is an gnutls_certificate_credentials_t structure.

CRL: is a list of trusted CRLs. They should have been verified before.

type: is DER or PEM

This function adds the trusted CRLs in order to verify client or server certificates. In case of a client this is not required to be called if the certificates are not verified using gnutls_certificate_verify_peers2(). This function may be called multiple times.

Returns the number of CRLs processed or a negative value on error.

— Function: int gnutls_certificate_set_x509_crl (gnutls_certificate_credentials_t res, gnutls_x509_crl_t * crl_list, int crl_list_size)

res: is an gnutls_certificate_credentials_t structure.

crl_list: is a list of trusted CRLs. They should have been verified before.

crl_list_size: holds the size of the crl_list

This function adds the trusted CRLs in order to verify client or server certificates. In case of a client this is not required to be called if the certificates are not verified using gnutls_certificate_verify_peers2(). This function may be called multiple times.

Returns 0 on success.

— Function: int gnutls_certificate_set_x509_key_file (gnutls_certificate_credentials_t res, const char * CERTFILE, const char * KEYFILE, gnutls_x509_crt_fmt_t type)

res: is an gnutls_certificate_credentials_t structure.

CERTFILE: is a file that containing the certificate list (path) for the specified private key, in PKCS7 format, or a list of certificates

KEYFILE: is a file that contains the private key

type: is PEM or DER

This function sets a certificate/private key pair in the gnutls_certificate_credentials_t structure. This function may be called more than once (in case multiple keys/certificates exist for the server).

Currently only PKCS-1 encoded RSA and DSA private keys are accepted by this function.

— Function: int gnutls_certificate_set_x509_key_mem (gnutls_certificate_credentials_t res, const gnutls_datum_t * cert, const gnutls_datum_t * key, gnutls_x509_crt_fmt_t type)

res: is an gnutls_certificate_credentials_t structure.

cert: contains a certificate list (path) for the specified private key

key: is the private key

type: is PEM or DER

This function sets a certificate/private key pair in the gnutls_certificate_credentials_t structure. This function may be called more than once (in case multiple keys/certificates exist for the server).

Currently are supported: RSA PKCS-1 encoded private keys, DSA private keys.

DSA private keys are encoded the OpenSSL way, which is an ASN.1 DER sequence of 6 INTEGERs - version, p, q, g, pub, priv.

Note that the keyUsage (2.5.29.15) PKIX extension in X.509 certificates is supported. This means that certificates intended for signing cannot be used for ciphersuites that require encryption.

If the certificate and the private key are given in PEM encoding then the strings that hold their values must be null terminated.

— Function: int gnutls_certificate_set_x509_key (gnutls_certificate_credentials_t res, gnutls_x509_crt_t * cert_list, int cert_list_size, gnutls_x509_privkey_t key)

res: is an gnutls_certificate_credentials_t structure.

cert_list: contains a certificate list (path) for the specified private key

cert_list_size: holds the size of the certificate list

key: is a gnutls_x509_privkey_t key

This function sets a certificate/private key pair in the gnutls_certificate_credentials_t structure. This function may be called more than once (in case multiple keys/certificates exist for the server).

— Function: int gnutls_certificate_set_x509_simple_pkcs12_file (gnutls_certificate_credentials_t res, const char * pkcs12file, gnutls_x509_crt_fmt_t type, const char * password)

res: is an gnutls_certificate_credentials_t structure.

pkcs12file: filename of file containing PKCS12 blob.

type: is PEM or DER of the pkcs12file.

password: optional password used to decrypt PKCS12 file, bags and keys.

This function sets a certificate/private key pair and/or a CRL in the gnutls_certificate_credentials_t structure. This function may be called more than once (in case multiple keys/certificates exist for the server).

MAC: ed PKCS12 files are supported. Encrypted PKCS12 bags are supported. Encrypted PKCS8 private keys are supported. However, only password based security, and the same password for all operations, are supported.

The private keys may be RSA PKCS1 or DSA private keys encoded in the OpenSSL way.

PKCS12 file may contain many keys and/or certificates, and there is no way to identify which key/certificate pair you want. You should make sure the PKCS12 file only contain one key/certificate pair and/or one CRL.

It is believed that the limitations of this function is acceptable for most usage, and that any more flexibility would introduce complexity that would make it harder to use this functionality at all.

Return value: Returns 0 on success, or an error code.

— Function: int gnutls_certificate_set_x509_trust_file (gnutls_certificate_credentials_t res, const char * cafile, gnutls_x509_crt_fmt_t type)

res: is an gnutls_certificate_credentials_t structure.

cafile: is a file containing the list of trusted CAs (DER or PEM list)

type: is PEM or DER

This function adds the trusted CAs in order to verify client or server certificates. In case of a client this is not required to be called if the certificates are not verified using gnutls_certificate_verify_peers2(). This function may be called multiple times.

In case of a server the names of the CAs set here will be sent to the client if a certificate request is sent. This can be disabled using gnutls_certificate_send_x509_rdn_sequence().

Returns the number of certificates processed or a negative value on error.

— Function: int gnutls_certificate_set_x509_trust_mem (gnutls_certificate_credentials_t res, const gnutls_datum_t * ca, gnutls_x509_crt_fmt_t type)

res: is an gnutls_certificate_credentials_t structure.

ca: is a list of trusted CAs or a DER certificate

type: is DER or PEM

This function adds the trusted CAs in order to verify client or server certificates. In case of a client this is not required to be called if the certificates are not verified using gnutls_certificate_verify_peers2(). This function may be called multiple times.

In case of a server the CAs set here will be sent to the client if a certificate request is sent. This can be disabled using gnutls_certificate_send_x509_rdn_sequence().

Returns the number of certificates processed or a negative value on error.

— Function: int gnutls_certificate_set_x509_trust (gnutls_certificate_credentials_t res, gnutls_x509_crt_t * ca_list, int ca_list_size)

res: is an gnutls_certificate_credentials_t structure.

ca_list: is a list of trusted CAs

ca_list_size: holds the size of the CA list

This function adds the trusted CAs in order to verify client or server certificates. In case of a client this is not required to be called if the certificates are not verified using gnutls_certificate_verify_peers2(). This function may be called multiple times.

In case of a server the CAs set here will be sent to the client if a certificate request is sent. This can be disabled using gnutls_certificate_send_x509_rdn_sequence().

Returns 0 on success.

— Function: const char * gnutls_certificate_type_get_name (gnutls_certificate_type_t type)

type: is a certificate type

Returns a string (or NULL) that contains the name of the specified certificate type.

— Function: gnutls_certificate_type_t gnutls_certificate_type_get (gnutls_session_t session)

session: is a gnutls_session_t structure.

Returns the currently used certificate type. The certificate type is by default X.509, unless it is negotiated as a TLS extension.

— Function: int gnutls_certificate_type_set_priority (gnutls_session_t session, const int * list)

session: is a gnutls_session_t structure.

list: is a 0 terminated list of gnutls_certificate_type_t elements.

Sets the priority on the certificate types supported by gnutls. Priority is higher for types specified before others. After specifying the types you want, you must append a 0. Note that the certificate type priority is set on the client. The server does not use the cert type priority except for disabling types that were not specified.

Returns 0 on success.

— Function: int gnutls_certificate_verify_peers2 (gnutls_session_t session, unsigned int * status)

session: is a gnutls session

status: is the output of the verification

This function will try to verify the peer's certificate and return its status (trusted, invalid etc.). The value of status should be one or more of the gnutls_certificate_status_t enumerated elements bitwise or'd. To avoid denial of service attacks some default upper limits regarding the certificate key size and chain size are set. To override them use gnutls_certificate_set_verify_limits().

Note that you must also check the peer's name in order to check if the verified certificate belongs to the actual peer.

Returns a negative error code on error and zero on success.

This is the same as gnutls_x509_verify_certificate() and uses the loaded CAs in the credentials as trusted CAs.

Note that some commonly used X.509 Certificate Authorities are still using Version 1 certificates. If you want to accept them, you need to call gnutls_certificate_set_verify_flags() with, e.g., GNUTLS_VERIFY_ALLOW_X509_V1_CA_CRT parameter.

— Function: int gnutls_certificate_verify_peers (gnutls_session_t session)

session: is a gnutls session

This function will try to verify the peer's certificate and return its status (trusted, invalid etc.). However you must also check the peer's name in order to check if the verified certificate belongs to the actual peer.

The return value should be one or more of the gnutls_certificate_status_t enumerated elements bitwise or'd, or a negative value on error.

This is the same as gnutls_x509_verify_certificate().

Deprecated: Use gnutls_certificate_verify_peers2() instead.

— Function: const char * gnutls_check_version (const char * req_version)

req_version: the version to check

Check that the version of the library is at minimum the requested one and return the version string; return NULL if the condition is not satisfied. If a NULL is passed to this function, no check is done, but the version string is simply returned.

— Function: size_t gnutls_cipher_get_key_size (gnutls_cipher_algorithm_t algorithm)

algorithm: is an encryption algorithm

Returns the length (in bytes) of the given cipher's key size. Returns 0 if the given cipher is invalid.

— Function: const char * gnutls_cipher_get_name (gnutls_cipher_algorithm_t algorithm)

algorithm: is an encryption algorithm

Returns a pointer to a string that contains the name of the specified cipher or NULL.

— Function: gnutls_cipher_algorithm_t gnutls_cipher_get (gnutls_session_t session)

session: is a gnutls_session_t structure.

Returns the currently used cipher.

— Function: int gnutls_cipher_set_priority (gnutls_session_t session, const int * list)

session: is a gnutls_session_t structure.

list: is a 0 terminated list of gnutls_cipher_algorithm_t elements.

Sets the priority on the ciphers supported by gnutls. Priority is higher for ciphers specified before others. After specifying the ciphers you want, you must append a 0. Note that the priority is set on the client. The server does not use the algorithm's priority except for disabling algorithms that were not specified.

Returns 0 on success.

— Function: const char * gnutls_cipher_suite_get_name (gnutls_kx_algorithm_t kx_algorithm, gnutls_cipher_algorithm_t cipher_algorithm, gnutls_mac_algorithm_t mac_algorithm)

kx_algorithm: is a Key exchange algorithm

cipher_algorithm: is a cipher algorithm

mac_algorithm: is a MAC algorithm

Returns a string that contains the name of a TLS cipher suite, specified by the given algorithms, or NULL.

Note that the full cipher suite name must be prepended by TLS or SSL depending of the protocol in use.

— Function: const char * gnutls_compression_get_name (gnutls_compression_method_t algorithm)

algorithm: is a Compression algorithm

Returns a pointer to a string that contains the name of the specified compression algorithm or NULL.

— Function: gnutls_compression_method_t gnutls_compression_get (gnutls_session_t session)

session: is a gnutls_session_t structure.

Returns the currently used compression method.

— Function: int gnutls_compression_set_priority (gnutls_session_t session, const int * list)

session: is a gnutls_session_t structure.

list: is a 0 terminated list of gnutls_compression_method_t elements.

Sets the priority on the compression algorithms supported by gnutls. Priority is higher for algorithms specified before others. After specifying the algorithms you want, you must append a 0. Note that the priority is set on the client. The server does not use the algorithm's priority except for disabling algorithms that were not specified.

TLS 1.0 does not define any compression algorithms except NULL. Other compression algorithms are to be considered as gnutls extensions.

Returns 0 on success.

— Function: void gnutls_credentials_clear (gnutls_session_t session)

session: is a gnutls_session_t structure.

Clears all the credentials previously set in this session.

— Function: int gnutls_credentials_set (gnutls_session_t session, gnutls_credentials_type_t type, void * cred)

session: is a gnutls_session_t structure.

type: is the type of the credentials

cred: is a pointer to a structure.

Sets the needed credentials for the specified type. Eg username, password - or public and private keys etc. The (void* cred) parameter is a structure that depends on the specified type and on the current session (client or server). [ In order to minimize memory usage, and share credentials between several threads gnutls keeps a pointer to cred, and not the whole cred structure. Thus you will have to keep the structure allocated until you call gnutls_deinit(). ]

For GNUTLS_CRD_ANON cred should be gnutls_anon_client_credentials_t in case of a client. In case of a server it should be gnutls_anon_server_credentials_t.

For GNUTLS_CRD_SRP cred should be gnutls_srp_client_credentials_t in case of a client, and gnutls_srp_server_credentials_t, in case of a server.

For GNUTLS_CRD_CERTIFICATE cred should be gnutls_certificate_credentials_t.

— Function: int gnutls_db_check_entry (gnutls_session_t session, gnutls_datum_t session_entry)

session: is a gnutls_session_t structure.

session_entry: is the session data (not key)

This function returns GNUTLS_E_EXPIRED, if the database entry has expired or 0 otherwise. This function is to be used when you want to clear unnesessary session which occupy space in your backend.

— Function: void * gnutls_db_get_ptr (gnutls_session_t session)

session: is a gnutls_session_t structure.

Returns the pointer that will be sent to db store, retrieve and delete functions, as the first argument.

— Function: void gnutls_db_remove_session (gnutls_session_t session)

session: is a gnutls_session_t structure.

This function will remove the current session data from the session database. This will prevent future handshakes reusing these session data. This function should be called if a session was terminated abnormally, and before gnutls_deinit() is called.

Normally gnutls_deinit() will remove abnormally terminated sessions.

— Function: void gnutls_db_set_cache_expiration (gnutls_session_t session, int seconds)

session: is a gnutls_session_t structure.

seconds: is the number of seconds.

Sets the expiration time for resumed sessions. The default is 3600 (one hour) at the time writing this.

— Function: void gnutls_db_set_ptr (gnutls_session_t session, void * ptr)

session: is a gnutls_session_t structure.

ptr: is the pointer

Sets the pointer that will be provided to db store, retrieve and delete functions, as the first argument.

— Function: void gnutls_db_set_remove_function (gnutls_session_t session, gnutls_db_remove_func rem_func)

session: is a gnutls_session_t structure.

rem_func: is the function.

Sets the function that will be used to remove data from the resumed sessions database. This function must return 0 on success.

The first argument to rem_func() will be null unless gnutls_db_set_ptr() has been called.

— Function: void gnutls_db_set_retrieve_function (gnutls_session_t session, gnutls_db_retr_func retr_func)

session: is a gnutls_session_t structure.

retr_func: is the function.

Sets the function that will be used to retrieve data from the resumed sessions database. This function must return a gnutls_datum_t containing the data on success, or a gnutls_datum_t containing null and 0 on failure.

The datum's data must be allocated using the function gnutls_malloc().

The first argument to retr_func() will be null unless gnutls_db_set_ptr() has been called.

— Function: void gnutls_db_set_store_function (gnutls_session_t session, gnutls_db_store_func store_func)

session: is a gnutls_session_t structure.

store_func: is the function

Sets the function that will be used to store data from the resumed sessions database. This function must remove 0 on success.

The first argument to store_func() will be null unless gnutls_db_set_ptr() has been called.

— Function: void gnutls_deinit (gnutls_session_t session)

session: is a gnutls_session_t structure.

This function clears all buffers associated with the session. This function will also remove session data from the session database if the session was terminated abnormally.

— Function: int gnutls_dh_get_group (gnutls_session_t session, gnutls_datum_t * raw_gen, gnutls_datum_t * raw_prime)

session: is a gnutls session

raw_gen: will hold the generator.

raw_prime: will hold the prime.

This function will return the group parameters used in the last Diffie Hellman authentication with the peer. These are the prime and the generator used. This function should be used for both anonymous and ephemeral diffie Hellman. The output parameters must be freed with gnutls_free().

Returns a negative value in case of an error.

— Function: int gnutls_dh_get_peers_public_bits (gnutls_session_t session)

session: is a gnutls session

This function will return the bits used in the last Diffie Hellman authentication with the peer. Should be used for both anonymous and ephemeral diffie Hellman. Returns a negative value in case of an error.

— Function: int gnutls_dh_get_prime_bits (gnutls_session_t session)

session: is a gnutls session

This function will return the bits of the prime used in the last Diffie Hellman authentication with the peer. Should be used for both anonymous and ephemeral diffie Hellman. Returns a negative value in case of an error.

— Function: int gnutls_dh_get_pubkey (gnutls_session_t session, gnutls_datum_t * raw_key)

session: is a gnutls session

raw_key: will hold the public key.

This function will return the peer's public key used in the last Diffie Hellman authentication. This function should be used for both anonymous and ephemeral diffie Hellman. The output parameters must be freed with gnutls_free().

Returns a negative value in case of an error.

— Function: int gnutls_dh_get_secret_bits (gnutls_session_t session)

session: is a gnutls session

This function will return the bits used in the last Diffie Hellman authentication with the peer. Should be used for both anonymous and ephemeral diffie Hellman. Returns a negative value in case of an error.

— Function: int gnutls_dh_params_cpy (gnutls_dh_params_t dst, gnutls_dh_params_t src)

dst: Is the destination structure, which should be initialized.

src: Is the source structure

This function will copy the DH parameters structure from source to destination.

— Function: void gnutls_dh_params_deinit (gnutls_dh_params_t dh_params)

dh_params: Is a structure that holds the prime numbers

This function will deinitialize the DH parameters structure.

— Function: int gnutls_dh_params_export_pkcs3 (gnutls_dh_params_t params, gnutls_x509_crt_fmt_t format, unsigned char * params_data, size_t * params_data_size)

params: Holds the DH parameters

format: the format of output params. One of PEM or DER.

params_data: will contain a PKCS3 DHParams structure PEM or DER encoded

params_data_size: holds the size of params_data (and will be replaced by the actual size of parameters)

This function will export the given dh parameters to a PKCS3 DHParams structure. This is the format generated by "openssl dhparam" tool. If the buffer provided is not long enough to hold the output, then GNUTLS_E_SHORT_MEMORY_BUFFER will be returned.

If the structure is PEM encoded, it will have a header of "BEGIN DH PARAMETERS".

In case of failure a negative value will be returned, and 0 on success.

— Function: int gnutls_dh_params_export_raw (gnutls_dh_params_t params, gnutls_datum_t * prime, gnutls_datum_t * generator, unsigned int * bits)

params: Holds the DH parameters

prime: will hold the new prime

generator: will hold the new generator

bits: if non null will hold is the prime's number of bits

This function will export the pair of prime and generator for use in the Diffie-Hellman key exchange. The new parameters will be allocated using gnutls_malloc() and will be stored in the appropriate datum.

— Function: int gnutls_dh_params_generate2 (gnutls_dh_params_t params, unsigned int bits)

params: Is the structure that the DH parameters will be stored

bits: is the prime's number of bits

This function will generate a new pair of prime and generator for use in the Diffie-Hellman key exchange. The new parameters will be allocated using gnutls_malloc() and will be stored in the appropriate datum. This function is normally slow.

Note that the bits value should be one of 768, 1024, 2048, 3072 or 4096. Also note that the DH parameters are only useful to servers. Since clients use the parameters sent by the server, it's of no use to call this in client side.

— Function: int gnutls_dh_params_import_pkcs3 (gnutls_dh_params_t params, const gnutls_datum_t * pkcs3_params, gnutls_x509_crt_fmt_t format)

params: A structure where the parameters will be copied to

pkcs3_params: should contain a PKCS3 DHParams structure PEM or DER encoded

format: the format of params. PEM or DER.

This function will extract the DHParams found in a PKCS3 formatted structure. This is the format generated by "openssl dhparam" tool.

If the structure is PEM encoded, it should have a header of "BEGIN DH PARAMETERS".

In case of failure a negative value will be returned, and 0 on success.

— Function: int gnutls_dh_params_import_raw (gnutls_dh_params_t dh_params, const gnutls_datum_t * prime, const gnutls_datum_t * generator)

dh_params: Is a structure that will hold the prime numbers

prime: holds the new prime

generator: holds the new generator

This function will replace the pair of prime and generator for use in the Diffie-Hellman key exchange. The new parameters should be stored in the appropriate gnutls_datum.

— Function: int gnutls_dh_params_init (gnutls_dh_params_t * dh_params)

dh_params: Is a structure that will hold the prime numbers

This function will initialize the DH parameters structure.

— Function: void gnutls_dh_set_prime_bits (gnutls_session_t session, unsigned int bits)

session: is a gnutls_session_t structure.

bits: is the number of bits

This function sets the number of bits, for use in an Diffie Hellman key exchange. This is used both in DH ephemeral and DH anonymous cipher suites. This will set the minimum size of the prime that will be used for the handshake.

In the client side it sets the minimum accepted number of bits. If a server sends a prime with less bits than that GNUTLS_E_DH_PRIME_UNACCEPTABLE will be returned by the handshake.

— Function: int gnutls_error_is_fatal (int error)

error: is an error returned by a gnutls function. Error should be a negative value.

If a function returns a negative value you may feed that value to this function to see if it is fatal. Returns 1 for a fatal error 0 otherwise. However you may want to check the error code manually, since some non-fatal errors to the protocol may be fatal for you (your program).

This is only useful if you are dealing with errors from the record layer or the handshake layer.

— Function: int gnutls_error_to_alert (int err, int * level)

err: is a negative integer

level: the alert level will be stored there

Returns an alert depending on the error code returned by a gnutls function. All alerts sent by this function should be considered fatal. The only exception is when err == GNUTLS_E_REHANDSHAKE, where a warning alert should be sent to the peer indicating that no renegotiation will be performed.

If the return value is GNUTLS_E_INVALID_REQUEST, then there was no mapping to an alert.

— Function: int gnutls_fingerprint (gnutls_digest_algorithm_t algo, const gnutls_datum_t * data, void * result, size_t * result_size)

algo: is a digest algorithm

data: is the data

result: is the place where the result will be copied (may be null).

result_size: should hold the size of the result. The actual size of the returned result will also be copied there.

This function will calculate a fingerprint (actually a hash), of the given data. The result is not printable data. You should convert it to hex, or to something else printable.

This is the usual way to calculate a fingerprint of an X.509 DER encoded certificate. Note however that the fingerprint of an OpenPGP is not just a hash and cannot be calculated with this function.

Returns a negative value in case of an error.

— Function: void gnutls_free (void * ptr)

This function will free data pointed by ptr.

The deallocation function used is the one set by gnutls_global_set_mem_functions().

— Function: void gnutls_global_deinit ( void)

This function deinitializes the global data, that were initialized using gnutls_global_init().

Note! This function is not thread safe. See the discussion for gnutls_global_init() for more information.

— Function: int gnutls_global_init ( void)

This function initializes the global data to defaults. Every gnutls application has a global data which holds common parameters shared by gnutls session structures. You must call gnutls_global_deinit() when gnutls usage is no longer needed Returns zero on success.

Note that this function will also initialize libgcrypt, if it has not been initialized before. Thus if you want to manually initialize libgcrypt you must do it before calling this function. This is useful in cases you want to disable libgcrypt's internal lockings etc.

This function increment a global counter, so that gnutls_global_deinit() only releases resources when it has been called as many times as gnutls_global_init(). This is useful when GnuTLS is used by more than one library in an application. This function can be called many times, but will only do something the first time.

Note! This function is not thread safe. If two threads call this function simultaneously, they can cause a race between checking the global counter and incrementing it, causing both threads to execute the library initialization code. That would lead to a memory leak. To handle this, your application could invoke this function after aquiring a thread mutex. To ignore the potential memory leak is also an option.

— Function: void gnutls_global_set_log_function (gnutls_log_func log_func)

log_func: it's a log function

This is the function where you set the logging function gnutls is going to use. This function only accepts a character array. Normally you may not use this function since it is only used for debugging purposes.

gnutls_log_func is of the form, void (*gnutls_log_func)( int level, const char*);

— Function: void gnutls_global_set_log_level (int level)

level: it's an integer from 0 to 9.

This is the function that allows you to set the log level. The level is an integer between 0 and 9. Higher values mean more verbosity. The default value is 0. Larger values should only be used with care, since they may reveal sensitive information.

Use a log level over 10 to enable all debugging options.

— Function: void gnutls_global_set_mem_functions (gnutls_alloc_function alloc_func, gnutls_alloc_function secure_alloc_func, gnutls_is_secure_function is_secure_func, gnutls_realloc_function realloc_func, gnutls_free_function free_func)

alloc_func: it's the default memory allocation function. Like malloc().

secure_alloc_func: This is the memory allocation function that will be used for sensitive data.

is_secure_func: a function that returns 0 if the memory given is not secure. May be NULL.

realloc_func: A realloc function

free_func: The function that frees allocated data. Must accept a NULL pointer.

This is the function were you set the memory allocation functions gnutls is going to use. By default the libc's allocation functions (malloc(), free()), are used by gnutls, to allocate both sensitive and not sensitive data. This function is provided to set the memory allocation functions to something other than the defaults (ie the gcrypt allocation functions).

This function must be called before gnutls_global_init() is called.

— Function: gnutls_handshake_description_t gnutls_handshake_get_last_in (gnutls_session_t session)

session: is a gnutls_session_t structure.

Returns the last handshake message received. This function is only useful to check where the last performed handshake failed. If the previous handshake succeed or was not performed at all then no meaningful value will be returned.

Check gnutls.h for the available handshake descriptions.

— Function: gnutls_handshake_description_t gnutls_handshake_get_last_out (gnutls_session_t session)

session: is a gnutls_session_t structure.

Returns the last handshake message sent. This function is only useful to check where the last performed handshake failed. If the previous handshake succeed or was not performed at all then no meaningful value will be returned.

Check gnutls.h for the available handshake descriptions.

— Function: void gnutls_handshake_set_max_packet_length (gnutls_session_t session, size_t max)

session: is a gnutls_session_t structure.

max: is the maximum number.

This function will set the maximum size of a handshake message. Handshake messages over this size are rejected. The default value is 16kb which is large enough. Set this to 0 if you do not want to set an upper limit.

— Function: void gnutls_handshake_set_private_extensions (gnutls_session_t session, int allow)

session: is a gnutls_session_t structure.

allow: is an integer (0 or 1)

This function will enable or disable the use of private cipher suites (the ones that start with 0xFF). By default or if allow is 0 then these cipher suites will not be advertized nor used.

Unless this function is called with the option to allow (1), then no compression algorithms, like LZO. That is because these algorithms are not yet defined in any RFC or even internet draft.

Enabling the private ciphersuites when talking to other than gnutls servers and clients may cause interoperability problems.

— Function: int gnutls_handshake (gnutls_session_t session)

session: is a gnutls_session_t structure.

This function does the handshake of the TLS/SSL protocol, and initializes the TLS connection.

This function will fail if any problem is encountered, and will return a negative error code. In case of a client, if the client has asked to resume a session, but the server couldn't, then a full handshake will be performed.

The non-fatal errors such as GNUTLS_E_AGAIN and GNUTLS_E_INTERRUPTED interrupt the handshake procedure, which should be later be resumed. Call this function again, until it returns 0; cf. gnutls_record_get_direction() and gnutls_error_is_fatal().

If this function is called by a server after a rehandshake request then GNUTLS_E_GOT_APPLICATION_DATA or GNUTLS_E_WARNING_ALERT_RECEIVED may be returned. Note that these are non fatal errors, only in the specific case of a rehandshake. Their meaning is that the client rejected the rehandshake request.

— Function: int gnutls_hex_decode (const gnutls_datum_t * hex_data, char * result, size_t * result_size)

hex_data: contain the encoded data

result: the place where decoded data will be copied

result_size: holds the size of the result

This function will decode the given encoded data, using the hex encoding used by PSK password files.

Note that hex_data should be null terminated.

Returns GNUTLS_E_SHORT_MEMORY_BUFFER if the buffer given is not long enough, or 0 on success.

— Function: int gnutls_hex_encode (const gnutls_datum_t * data, char * result, size_t * result_size)

data: contain the raw data

result: the place where hex data will be copied

result_size: holds the size of the result

This function will convert the given data to printable data, using the hex encoding, as used in the PSK password files.

Returns GNUTLS_E_SHORT_MEMORY_BUFFER if the buffer given is not long enough, or 0 on success.

— Function: int gnutls_init (gnutls_session_t * session, gnutls_connection_end_t con_end)

session: is a pointer to a gnutls_session_t structure.

con_end: is used to indicate if this session is to be used for server or client. Can be one of GNUTLS_CLIENT and GNUTLS_SERVER.

This function initializes the current session to null. Every session must be initialized before use, so internal structures can be allocated. This function allocates structures which can only be free'd by calling gnutls_deinit(). Returns zero on success.

— Function: const char * gnutls_kx_get_name (gnutls_kx_algorithm_t algorithm)

algorithm: is a key exchange algorithm

Returns a pointer to a string that contains the name of the specified key exchange algorithm or NULL.

— Function: gnutls_kx_algorithm_t gnutls_kx_get (gnutls_session_t session)

session: is a gnutls_session_t structure.

Returns the key exchange algorithm used in the last handshake.

— Function: int gnutls_kx_set_priority (gnutls_session_t session, const int * list)

session: is a gnutls_session_t structure.

list: is a 0 terminated list of gnutls_kx_algorithm_t elements.

Sets the priority on the key exchange algorithms supported by gnutls. Priority is higher for algorithms specified before others. After specifying the algorithms you want, you must append a 0. Note that the priority is set on the client. The server does not use the algorithm's priority except for disabling algorithms that were not specified.

Returns 0 on success.

— Function: const char * gnutls_mac_get_name (gnutls_mac_algorithm_t algorithm)

algorithm: is a MAC algorithm

Returns a string that contains the name of the specified MAC algorithm or NULL.

— Function: gnutls_mac_algorithm_t gnutls_mac_get (gnutls_session_t session)

session: is a gnutls_session_t structure.

Returns the currently used mac algorithm.

— Function: int gnutls_mac_set_priority (gnutls_session_t session, const int * list)

session: is a gnutls_session_t structure.

list: is a 0 terminated list of gnutls_mac_algorithm_t elements.

Sets the priority on the mac algorithms supported by gnutls. Priority is higher for algorithms specified before others. After specifying the algorithms you want, you must append a 0. Note that the priority is set on the client. The server does not use the algorithm's priority except for disabling algorithms that were not specified.

Returns 0 on success.

— Function: void * gnutls_malloc (size_t s)

This function will allocate 's' bytes data, and return a pointer to memory. This function is supposed to be used by callbacks.

The allocation function used is the one set by gnutls_global_set_mem_functions().

— Function: void gnutls_openpgp_send_key (gnutls_session_t session, gnutls_openpgp_key_status_t status)

session: is a pointer to a gnutls_session_t structure.

status: is one of OPENPGP_KEY, or OPENPGP_KEY_FINGERPRINT

This function will order gnutls to send the key fingerprint instead of the key in the initial handshake procedure. This should be used with care and only when there is indication or knowledge that the server can obtain the client's key.

— Function: int gnutls_pem_base64_decode_alloc (const char * header, const gnutls_datum_t * b64_data, gnutls_datum_t * result)

header: The PEM header (eg. CERTIFICATE)

b64_data: contains the encoded data

result: the place where decoded data lie

This function will decode the given encoded data. The decoded data will be allocated, and stored into result. If the header given is non null this function will search for "——BEGIN header" and decode only this part. Otherwise it will decode the first PEM packet found.

You should use gnutls_free() to free the returned data.

— Function: int gnutls_pem_base64_decode (const char * header, const gnutls_datum_t * b64_data, unsigned char * result, size_t * result_size)

header: A null terminated string with the PEM header (eg. CERTIFICATE)

b64_data: contain the encoded data

result: the place where decoded data will be copied

result_size: holds the size of the result

This function will decode the given encoded data. If the header given is non null this function will search for "——BEGIN header" and decode only this part. Otherwise it will decode the first PEM packet found.

Returns GNUTLS_E_SHORT_MEMORY_BUFFER if the buffer given is not long enough, or 0 on success.

— Function: int gnutls_pem_base64_encode_alloc (const char * msg, const gnutls_datum_t * data, gnutls_datum_t * result)

msg: is a message to be put in the encoded header

data: contains the raw data

result: will hold the newly allocated encoded data

This function will convert the given data to printable data, using the base64 encoding. This is the encoding used in PEM messages. This function will allocate the required memory to hold the encoded data.

You should use gnutls_free() to free the returned data.

— Function: int gnutls_pem_base64_encode (const char * msg, const gnutls_datum_t * data, char * result, size_t * result_size)

msg: is a message to be put in the header

data: contain the raw data

result: the place where base64 data will be copied

result_size: holds the size of the result

This function will convert the given data to printable data, using the base64 encoding. This is the encoding used in PEM messages. If the provided buffer is not long enough GNUTLS_E_SHORT_MEMORY_BUFFER is returned.

The output string will be null terminated, although the size will not include the terminating null.

— Function: void gnutls_perror (int error)

error: is an error returned by a gnutls function. Error is always a negative value.

This function is like perror(). The only difference is that it accepts an error number returned by a gnutls function.

— Function: const char * gnutls_pk_algorithm_get_name (gnutls_pk_algorithm_t algorithm)

algorithm: is a pk algorithm

Returns a string that contains the name of the specified public key algorithm or NULL.

— Function: int gnutls_prf_raw (gnutls_session_t session, size_t label_size, const char * label, size_t seed_size, const char * seed, size_t outsize, char * out)

session: is a gnutls_session_t structure.

label_size: length of the label variable.

label: label used in PRF computation, typically a short string.

seed_size: length of the seed variable.

seed: optional extra data to seed the PRF with.

outsize: size of pre-allocated output buffer to hold the output.

out: pre-allocate buffer to hold the generated data.

Apply the TLS Pseudo-Random-Function (PRF) using the master secret on some data.

The label variable usually contain a string denoting the purpose for the generated data. The seed usually contain data such as the client and server random, perhaps together with some additional data that is added to guarantee uniqueness of the output for a particular purpose.

Because the output is not guaranteed to be unique for a particular session unless seed include the client random and server random fields (the PRF would output the same data on another connection resumed from the first one), it is not recommended to use this function directly. The gnutls_prf() function seed the PRF with the client and server random fields directly, and is recommended if you want to generate pseudo random data unique for each session.

Return value: Return 0 on success, or an error code.

— Function: int gnutls_prf (gnutls_session_t session, size_t label_size, const char * label, int server_random_first, size_t extra_size, const char * extra, size_t outsize, char * out)

session: is a gnutls_session_t structure.

label_size: length of the label variable.

label: label used in PRF computation, typically a short string.

server_random_first: non-0 if server random field should be first in seed

extra_size: length of the extra variable.

extra: optional extra data to seed the PRF with.

outsize: size of pre-allocated output buffer to hold the output.

out: pre-allocate buffer to hold the generated data.

Apply the TLS Pseudo-Random-Function (PRF) using the master secret on some data, seeded with the client and server random fields.

The label variable usually contain a string denoting the purpose for the generated data. The server_random_first indicate whether the client random field or the server random field should be first in the seed. Non-0 indicate that the server random field is first, 0 that the client random field is first.

The extra variable can be used to add more data to the seed, after the random variables. It can be used to tie make sure the generated output is strongly connected to some additional data (e.g., a string used in user authentication).

The output is placed in *OUT, which must be pre-allocated.

Return value: Return 0 on success, or an error code.

— Function: const char * gnutls_protocol_get_name (gnutls_protocol_t version)

version: is a (gnutls) version number

Returns a string that contains the name of the specified TLS version or NULL.

— Function: gnutls_protocol_t gnutls_protocol_get_version (gnutls_session_t session)

session: is a gnutls_session_t structure.

Returns the version of the currently used protocol.

— Function: int gnutls_protocol_set_priority (gnutls_session_t session, const int * list)

session: is a gnutls_session_t structure.

list: is a 0 terminated list of gnutls_protocol_t elements.

Sets the priority on the protocol versions supported by gnutls. This function actually enables or disables protocols. Newer protocol versions always have highest priority.

Returns 0 on success.

— Function: int gnutls_psk_allocate_client_credentials (gnutls_psk_client_credentials_t * sc)

sc: is a pointer to an gnutls_psk_server_credentials_t structure.

This structure is complex enough to manipulate directly thus this helper function is provided in order to allocate it.

Returns 0 on success.

— Function: int gnutls_psk_allocate_server_credentials (gnutls_psk_server_credentials_t * sc)

sc: is a pointer to an gnutls_psk_server_credentials_t structure.

This structure is complex enough to manipulate directly thus this helper function is provided in order to allocate it.

Returns 0 on success.

— Function: void gnutls_psk_free_client_credentials (gnutls_psk_client_credentials_t sc)

sc: is an gnutls_psk_client_credentials_t structure.

This structure is complex enough to manipulate directly thus this helper function is provided in order to free (deallocate) it.

— Function: void gnutls_psk_free_server_credentials (gnutls_psk_server_credentials_t sc)

sc: is an gnutls_psk_server_credentials_t structure.

This structure is complex enough to manipulate directly thus this helper function is provided in order to free (deallocate) it.

— Function: const char * gnutls_psk_server_get_username (gnutls_session_t session)

session: is a gnutls session

This function will return the username of the peer. This should only be called in case of PSK authentication and in case of a server. Returns NULL in case of an error.

— Function: void gnutls_psk_set_client_credentials_function (gnutls_psk_client_credentials_t cred, gnutls_psk_client_credentials_function * func)

cred: is a gnutls_psk_server_credentials_t structure.

func: is the callback function

This function can be used to set a callback to retrieve the username and password for client PSK authentication. The callback's function form is: int (*callback)(gnutls_session_t, char** username, gnutls_datum* key);

The username and key must be allocated using gnutls_malloc(). username should be ASCII strings or UTF-8 strings prepared using the "SASLprep" profile of "stringprep".

The callback function will be called once per handshake.

The callback function should return 0 on success. -1 indicates an error.

— Function: int gnutls_psk_set_client_credentials (gnutls_psk_client_credentials_t res, const char * username, const gnutls_datum * key, unsigned int flags)

res: is an gnutls_psk_client_credentials_t structure.

username: is the user's zero-terminated userid

key: is the user's key

This function sets the username and password, in a gnutls_psk_client_credentials_t structure. Those will be used in PSK authentication. username should be an ASCII string or UTF-8 strings prepared using the "SASLprep" profile of "stringprep". The key can be either in raw byte format or in Hex (not with the '0x' prefix).

Returns 0 on success.

— Function: void gnutls_psk_set_params_function (gnutls_psk_server_credentials_t res, gnutls_params_function * func)

res: is a gnutls_psk_server_credentials_t structure

func: is the function to be called

This function will set a callback in order for the server to get the diffie hellman or RSA parameters for psk authentication. The callback should return zero on success.

— Function: int gnutls_psk_set_server_credentials_file (gnutls_psk_server_credentials_t res, const char * password_file)

res: is an gnutls_psk_server_credentials_t structure.

password_file: is the PSK password file (passwd.psk)

This function sets the password file, in a gnutls_psk_server_credentials_t structure. This password file holds usernames and keys and will be used for PSK authentication.

Returns 0 on success.

— Function: void gnutls_psk_set_server_credentials_function (gnutls_psk_server_credentials_t cred, gnutls_psk_server_credentials_function * func)

cred: is a gnutls_psk_server_credentials_t structure.

func: is the callback function

This function can be used to set a callback to retrieve the user's PSK credentials. The callback's function form is: int (*callback)(gnutls_session_t, const char* username, gnutls_datum_t* key);

username contains the actual username. The key must be filled in using the gnutls_malloc().

In case the callback returned a negative number then gnutls will assume that the username does not exist.

The callback function will only be called once per handshake. The callback function should return 0 on success, while -1 indicates an error.

— Function: void gnutls_psk_set_server_dh_params (gnutls_psk_server_credentials_t res, gnutls_dh_params_t dh_params)

res: is a gnutls_psk_server_credentials_t structure

dh_params: is a structure that holds diffie hellman parameters.

This function will set the diffie hellman parameters for an anonymous server to use. These parameters will be used in Diffie Hellman with PSK cipher suites.

— Function: void gnutls_psk_set_server_params_function (gnutls_psk_server_credentials_t res, gnutls_params_function * func)

res: is a gnutls_certificate_credentials_t structure

func: is the function to be called

This function will set a callback in order for the server to get the diffie hellman parameters for PSK authentication. The callback should return zero on success.

— Function: size_t gnutls_record_check_pending (gnutls_session_t session)

session: is a gnutls_session_t structure.

This function checks if there are any data to receive in the gnutls buffers. Returns the size of that data or 0. Notice that you may also use select() to check for data in a TCP connection, instead of this function. (gnutls leaves some data in the tcp buffer in order for select to work).

— Function: int gnutls_record_get_direction (gnutls_session_t session)

session: is a gnutls_session_t structure.

This function provides information about the internals of the record protocol and is only useful if a prior gnutls function call (e.g. gnutls_handshake()) was interrupted for some reason, that is, if a function returned GNUTLS_E_INTERRUPTED or GNUTLS_E_AGAIN. In such a case, you might want to call select() or poll() before calling the interrupted gnutls function again. To tell you whether a file descriptor should be selected for either reading or writing, gnutls_record_get_direction() returns 0 if the interrupted function was trying to read data, and 1 if it was trying to write data.

— Function: size_t gnutls_record_get_max_size (gnutls_session_t session)

session: is a gnutls_session_t structure.

This function returns the maximum record packet size in this connection. The maximum record size is negotiated by the client after the first handshake message.

— Function: ssize_t gnutls_record_recv (gnutls_session_t session, void * data, size_t sizeofdata)

session: is a gnutls_session_t structure.

data: the buffer that the data will be read into

sizeofdata: the number of requested bytes

This function has the similar semantics with recv(). The only difference is that is accepts a GNUTLS session, and uses different error codes.

In the special case that a server requests a renegotiation, the client may receive an error code of GNUTLS_E_REHANDSHAKE. This message may be simply ignored, replied with an alert containing NO_RENEGOTIATION, or replied with a new handshake, depending on the client's will.

If EINTR is returned by the internal push function (the default is code{recv()}) then GNUTLS_E_INTERRUPTED will be returned. If GNUTLS_E_INTERRUPTED or GNUTLS_E_AGAIN is returned, you must call this function again, with the same parameters; alternatively you could provide a NULL pointer for data, and 0 for size. cf. code{gnutls_record_get_direction()}.

A server may also receive GNUTLS_E_REHANDSHAKE when a client has initiated a handshake. In that case the server can only initiate a handshake or terminate the connection.

Returns the number of bytes received and zero on EOF. A negative error code is returned in case of an error. The number of bytes received might be less than code{count}.

— Function: ssize_t gnutls_record_send (gnutls_session_t session, const void * data, size_t sizeofdata)

session: is a gnutls_session_t structure.

data: contains the data to send

sizeofdata: is the length of the data

This function has the similar semantics with send(). The only difference is that is accepts a GNUTLS session, and uses different error codes.

Note that if the send buffer is full, send() will block this function. See the send() documentation for full information. You can replace the default push function by using gnutls_transport_set_ptr2() with a call to send() with a MSG_DONTWAIT flag if blocking is a problem.

If the EINTR is returned by the internal push function (the default is send()} then GNUTLS_E_INTERRUPTED will be returned. If GNUTLS_E_INTERRUPTED or GNUTLS_E_AGAIN is returned, you must call this function again, with the same parameters; alternatively you could provide a NULL pointer for data, and 0 for size. cf. gnutls_record_get_direction().

Returns the number of bytes sent, or a negative error code. The number of bytes sent might be less than sizeofdata. The maximum number of bytes this function can send in a single call depends on the negotiated maximum record size.

— Function: ssize_t gnutls_record_set_max_size (gnutls_session_t session, size_t size)

session: is a gnutls_session_t structure.

size: is the new size

This function sets the maximum record packet size in this connection. This property can only be set to clients. The server may choose not to accept the requested size.

Acceptable values are 512(=2^9), 1024(=2^10), 2048(=2^11) and 4096(=2^12). Returns 0 on success. The requested record size does get in effect immediately only while sending data. The receive part will take effect after a successful handshake.

This function uses a TLS extension called 'max record size'. Not all TLS implementations use or even understand this extension.

— Function: int gnutls_rehandshake (gnutls_session_t session)

session: is a gnutls_session_t structure.

This function will renegotiate security parameters with the client. This should only be called in case of a server.

This message informs the peer that we want to renegotiate parameters (perform a handshake).

If this function succeeds (returns 0), you must call the gnutls_handshake() function in order to negotiate the new parameters.

If the client does not wish to renegotiate parameters he will should with an alert message, thus the return code will be GNUTLS_E_WARNING_ALERT_RECEIVED and the alert will be GNUTLS_A_NO_RENEGOTIATION. A client may also choose to ignore this message.

— Function: int gnutls_rsa_export_get_modulus_bits (gnutls_session_t session)

session: is a gnutls session

This function will return the bits used in the last RSA-EXPORT key exchange with the peer. Returns a negative value in case of an error.

— Function: int gnutls_rsa_export_get_pubkey (gnutls_session_t session, gnutls_datum_t * exponent, gnutls_datum_t * modulus)

session: is a gnutls session

exponent: will hold the exponent.

modulus: will hold the modulus.

This function will return the peer's public key exponent and modulus used in the last RSA-EXPORT authentication. The output parameters must be freed with gnutls_free().

Returns a negative value in case of an error.

— Function: int gnutls_rsa_params_cpy (gnutls_rsa_params_t dst, gnutls_rsa_params_t src)

dst: Is the destination structure, which should be initialized.

src: Is the source structure

This function will copy the RSA parameters structure from source to destination.

— Function: void gnutls_rsa_params_deinit (gnutls_rsa_params_t rsa_params)

rsa_params: Is a structure that holds the parameters

This function will deinitialize the RSA parameters structure.

— Function: int gnutls_rsa_params_export_pkcs1 (gnutls_rsa_params_t params, gnutls_x509_crt_fmt_t format, unsigned char * params_data, size_t * params_data_size)

params: Holds the RSA parameters

format: the format of output params. One of PEM or DER.

params_data: will contain a PKCS1 RSAPublicKey structure PEM or DER encoded

params_data_size: holds the size of params_data (and will be replaced by the actual size of parameters)

This function will export the given RSA parameters to a PKCS1 RSAPublicKey structure. If the buffer provided is not long enough to hold the output, then GNUTLS_E_SHORT_MEMORY_BUFFER will be returned.

If the structure is PEM encoded, it will have a header of "BEGIN RSA PRIVATE KEY".

In case of failure a negative value will be returned, and 0 on success.

— Function: int gnutls_rsa_params_export_raw (gnutls_rsa_params_t params, gnutls_datum_t * m, gnutls_datum_t * e, gnutls_datum_t * d, gnutls_datum_t * p, gnutls_datum_t * q, gnutls_datum_t * u, unsigned int * bits)

params: a structure that holds the rsa parameters

m: will hold the modulus

e: will hold the public exponent

d: will hold the private exponent

p: will hold the first prime (p)

q: will hold the second prime (q)

u: will hold the coefficient

bits: if non null will hold the prime's number of bits

This function will export the RSA parameters found in the given structure. The new parameters will be allocated using gnutls_malloc() and will be stored in the appropriate datum.

— Function: int gnutls_rsa_params_generate2 (gnutls_rsa_params_t params, unsigned int bits)

params: The structure where the parameters will be stored

bits: is the prime's number of bits

This function will generate new temporary RSA parameters for use in RSA-EXPORT ciphersuites. This function is normally slow.

Note that if the parameters are to be used in export cipher suites the bits value should be 512 or less. Also note that the generation of new RSA parameters is only useful to servers. Clients use the parameters sent by the server, thus it's no use calling this in client side.

— Function: int gnutls_rsa_params_import_pkcs1 (gnutls_rsa_params_t params, const gnutls_datum_t * pkcs1_params, gnutls_x509_crt_fmt_t format)

params: A structure where the parameters will be copied to

pkcs1_params: should contain a PKCS1 RSAPublicKey structure PEM or DER encoded

format: the format of params. PEM or DER.

This function will extract the RSAPublicKey found in a PKCS1 formatted structure.

If the structure is PEM encoded, it should have a header of "BEGIN RSA PRIVATE KEY".

In case of failure a negative value will be returned, and 0 on success.

— Function: int gnutls_rsa_params_import_raw (gnutls_rsa_params_t rsa_params, const gnutls_datum_t * m, const gnutls_datum_t * e, const gnutls_datum_t * d, const gnutls_datum_t * p, const gnutls_datum_t * q, const gnutls_datum_t * u)

rsa_params: Is a structure will hold the parameters

m: holds the modulus

e: holds the public exponent

d: holds the private exponent

p: holds the first prime (p)

q: holds the second prime (q)

u: holds the coefficient

This function will replace the parameters in the given structure. The new parameters should be stored in the appropriate gnutls_datum.

— Function: int gnutls_rsa_params_init (gnutls_rsa_params_t * rsa_params)

rsa_params: Is a structure that will hold the parameters

This function will initialize the temporary RSA parameters structure.

— Function: int gnutls_server_name_get (gnutls_session_t session, void * data, size_t * data_length, unsigned int * type, unsigned int indx)

session: is a gnutls_session_t structure.

data: will hold the data

data_length: will hold the data length. Must hold the maximum size of data.

type: will hold the server name indicator type

indx: is the index of the server_name

This function will allow you to get the name indication (if any), a client has sent. The name indication may be any of the enumeration gnutls_server_name_type_t.

If type is GNUTLS_NAME_DNS, then this function is to be used by servers that support virtual hosting, and the data will be a null terminated UTF-8 string.

If data has not enough size to hold the server name GNUTLS_E_SHORT_MEMORY_BUFFER is returned, and data_length will hold the required size.

index is used to retrieve more than one server names (if sent by the client). The first server name has an index of 0, the second 1 and so on. If no name with the given index exists GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE is returned.

— Function: int gnutls_server_name_set (gnutls_session_t session, gnutls_server_name_type_t type, const void * name, size_t name_length)

session: is a gnutls_session_t structure.

type: specifies the indicator type

name: is a string that contains the server name.

name_length: holds the length of name

This function is to be used by clients that want to inform (via a TLS extension mechanism) the server of the name they connected to. This should be used by clients that connect to servers that do virtual hosting.

The value of name depends on the ind type. In case of GNUTLS_NAME_DNS, an ASCII or UTF-8 null terminated string, without the trailing dot, is expected. IPv4 or IPv6 addresses are not permitted.

— Function: const void * gnutls_session_get_client_random (gnutls_session_t session)

session: is a gnutls_session_t structure.

Return a pointer to the 32-byte client random field used in the session. The pointer must not be modified or deallocated.

If a client random value has not yet been established, the output will be garbage; in particular, a NULL return value should not be expected.

Return value: pointer to client random.

— Function: int gnutls_session_get_data2 (gnutls_session_t session, gnutls_datum * data)

session: is a gnutls_session_t structure.

Returns all session parameters, in order to support resuming. The client should call this, and keep the returned session, if he wants to resume that current version later by calling gnutls_session_set_data() This function must be called after a successful handshake. The returned datum must be freed with gnutls_free().

Resuming sessions is really useful and speedups connections after a succesful one.

— Function: int gnutls_session_get_data (gnutls_session_t session, void * session_data, size_t * session_data_size)

session: is a gnutls_session_t structure.

session_data: is a pointer to space to hold the session.

session_data_size: is the session_data's size, or it will be set by the function.

Returns all session parameters, in order to support resuming. The client should call this, and keep the returned session, if he wants to resume that current version later by calling gnutls_session_set_data() This function must be called after a successful handshake.

Resuming sessions is really useful and speedups connections after a succesful one.

— Function: int gnutls_session_get_id (gnutls_session_t session, void * session_id, size_t * session_id_size)

session: is a gnutls_session_t structure.

session_id: is a pointer to space to hold the session id.

session_id_size: is the session id's size, or it will be set by the function.

Returns the current session id. This can be used if you want to check if the next session you tried to resume was actually resumed. This is because resumed sessions have the same sessionID with the original session.

Session id is some data set by the server, that identify the current session. In TLS 1.0 and SSL 3.0 session id is always less than 32 bytes.

Returns zero on success.

— Function: const void * gnutls_session_get_master_secret (gnutls_session_t session)

session: is a gnutls_session_t structure.

Return a pointer to the 48-byte master secret in the session. The pointer must not be modified or deallocated.

If a master secret value has not yet been established, the output will be garbage; in particular, a NULL return value should not be expected.

Consider using gnutls_prf() rather than extracting the master secret and use it to derive further data.

Return value: pointer to master secret.

— Function: void * gnutls_session_get_ptr (gnutls_session_t session)

session: is a gnutls_session_t structure.

This function will return the user given pointer from the session structure. This is the pointer set with gnutls_session_set_ptr().

— Function: const void * gnutls_session_get_server_random (gnutls_session_t session)

session: is a gnutls_session_t structure.

Return a pointer to the 32-byte server random field used in the session. The pointer must not be modified or deallocated.

If a server random value has not yet been established, the output will be garbage; in particular, a NULL return value should not be expected.

Return value: pointer to server random.

— Function: int gnutls_session_is_resumed (gnutls_session_t session)

session: is a gnutls_session_t structure.

This function will return non zero if this session is a resumed one, or a zero if this is a new session.

— Function: int gnutls_session_set_data (gnutls_session_t session, const void * session_data, size_t session_data_size)

session: is a gnutls_session_t structure.

session_data: is a pointer to space to hold the session.

session_data_size: is the session's size

Sets all session parameters, in order to resume a previously established session. The session data given must be the one returned by gnutls_session_get_data(). This function should be called before gnutls_handshake().

Keep in mind that session resuming is advisory. The server may choose not to resume the session, thus a full handshake will be performed.

Returns a negative value on error.

— Function: void gnutls_session_set_ptr (gnutls_session_t session, void * ptr)

session: is a gnutls_session_t structure.

ptr: is the user pointer

This function will set (associate) the user given pointer to the session structure. This is pointer can be accessed with gnutls_session_get_ptr().

— Function: int gnutls_set_default_export_priority (gnutls_session_t session)

session: is a gnutls_session_t structure.

Sets some default priority on the ciphers, key exchange methods, macs and compression methods. This is to avoid using the gnutls_*_priority() functions, if these defaults are ok. This function also includes weak algorithms. The order is TLS1, SSL3 for protocols, RSA, DHE_DSS, DHE_RSA, RSA_EXPORT for key exchange algorithms. SHA, MD5, RIPEMD160 for MAC algorithms, AES_256_CBC, AES_128_CBC, and 3DES_CBC, ARCFOUR_128, ARCFOUR_40 for ciphers.

Returns 0 on success.

— Function: int gnutls_set_default_priority (gnutls_session_t session)

session: is a gnutls_session_t structure.

Sets some default priority on the ciphers, key exchange methods, macs and compression methods. This is to avoid using the gnutls_*_priority() functions, if these defaults are ok. You may override any of the following priorities by calling the appropriate functions.

The order is TLS1, SSL3 for protocols. RSA, DHE_DSS, DHE_RSA for key exchange algorithms. SHA, MD5 and RIPEMD160 for MAC algorithms. AES_128_CBC, 3DES_CBC, and ARCFOUR_128 for ciphers.

Returns 0 on success.

— Function: const char * gnutls_sign_algorithm_get_name (gnutls_sign_algorithm_t sign)

Returns a string that contains the name of the specified sign algorithm or NULL.

— Function: int gnutls_srp_allocate_client_credentials (gnutls_srp_client_credentials_t * sc)

sc: is a pointer to an gnutls_srp_server_credentials_t structure.

This structure is complex enough to manipulate directly thus this helper function is provided in order to allocate it.

Returns 0 on success.

— Function: int gnutls_srp_allocate_server_credentials (gnutls_srp_server_credentials_t * sc)

sc: is a pointer to an gnutls_srp_server_credentials_t structure.

This structure is complex enough to manipulate directly thus this helper function is provided in order to allocate it.

Returns 0 on success.

— Function: int gnutls_srp_base64_decode_alloc (const gnutls_datum_t * b64_data, gnutls_datum_t * result)

b64_data: contains the encoded data

result: the place where decoded data lie

This function will decode the given encoded data. The decoded data will be allocated, and stored into result. It will decode using the base64 algorithm found in libsrp.

You should use gnutls_free() to free the returned data.

— Function: int gnutls_srp_base64_decode (const gnutls_datum_t * b64_data, char * result, size_t * result_size)

b64_data: contain the encoded data

result: the place where decoded data will be copied

result_size: holds the size of the result

This function will decode the given encoded data, using the base64 encoding found in libsrp.

Note that b64_data should be null terminated.

Returns GNUTLS_E_SHORT_MEMORY_BUFFER if the buffer given is not long enough, or 0 on success.

— Function: int gnutls_srp_base64_encode_alloc (const gnutls_datum_t * data, gnutls_datum_t * result)

data: contains the raw data

result: will hold the newly allocated encoded data

This function will convert the given data to printable data, using the base64 encoding. This is the encoding used in SRP password files. This function will allocate the required memory to hold the encoded data.

You should use gnutls_free() to free the returned data.

— Function: int gnutls_srp_base64_encode (const gnutls_datum_t * data, char * result, size_t * result_size)

data: contain the raw data

result: the place where base64 data will be copied

result_size: holds the size of the result

This function will convert the given data to printable data, using the base64 encoding, as used in the libsrp. This is the encoding used in SRP password files. If the provided buffer is not long enough GNUTLS_E_SHORT_MEMORY_BUFFER is returned.

— Function: void gnutls_srp_free_client_credentials (gnutls_srp_client_credentials_t sc)

sc: is an gnutls_srp_client_credentials_t structure.

This structure is complex enough to manipulate directly thus this helper function is provided in order to free (deallocate) it.

— Function: void gnutls_srp_free_server_credentials (gnutls_srp_server_credentials_t sc)

sc: is an gnutls_srp_server_credentials_t structure.

This structure is complex enough to manipulate directly thus this helper function is provided in order to free (deallocate) it.

— Function: const char * gnutls_srp_server_get_username (gnutls_session_t session)

session: is a gnutls session

This function will return the username of the peer. This should only be called in case of SRP authentication and in case of a server. Returns NULL in case of an error.

— Function: void gnutls_srp_set_client_credentials_function (gnutls_srp_client_credentials_t cred, gnutls_srp_client_credentials_function * func)

cred: is a gnutls_srp_server_credentials_t structure.

func: is the callback function

This function can be used to set a callback to retrieve the username and password for client SRP authentication. The callback's function form is: int (*callback)(gnutls_session_t, unsigned int times, char** username, char** password);

The username and password must be allocated using gnutls_malloc(). times will be 0 the first time called, and 1 the second. username and password should be ASCII strings or UTF-8 strings prepared using the "SASLprep" profile of "stringprep".

The callback function will be called once or twice per handshake. The first time called, is before the ciphersuite is negotiated. At that time if the callback returns a negative error code, the callback will be called again if SRP has been negotiated. This uses a special TLS-SRP idiom in order to avoid asking the user for SRP password and username if the server does not support SRP.

The callback should not return a negative error code the second time called, since the handshake procedure will be aborted.

The callback function should return 0 on success. -1 indicates an error.

— Function: int gnutls_srp_set_client_credentials (gnutls_srp_client_credentials_t res, const char * username, const char * password)

res: is an gnutls_srp_client_credentials_t structure.

username: is the user's userid

password: is the user's password

This function sets the username and password, in a gnutls_srp_client_credentials_t structure. Those will be used in SRP authentication. username and password should be ASCII strings or UTF-8 strings prepared using the "SASLprep" profile of "stringprep".

Returns 0 on success.

— Function: int gnutls_srp_set_server_credentials_file (gnutls_srp_server_credentials_t res, const char * password_file, const char * password_conf_file)

res: is an gnutls_srp_server_credentials_t structure.

password_file: is the SRP password file (tpasswd)

password_conf_file: is the SRP password conf file (tpasswd.conf)

This function sets the password files, in a gnutls_srp_server_credentials_t structure. Those password files hold usernames and verifiers and will be used for SRP authentication.

Returns 0 on success.

— Function: void gnutls_srp_set_server_credentials_function (gnutls_srp_server_credentials_t cred, gnutls_srp_server_credentials_function * func)

cred: is a gnutls_srp_server_credentials_t structure.

func: is the callback function

This function can be used to set a callback to retrieve the user's SRP credentials. The callback's function form is: int (*callback)(gnutls_session_t, const char* username, gnutls_datum_t* salt, gnutls_datum_t *verifier, gnutls_datum_t* g, gnutls_datum_t* n);

username contains the actual username. The salt, verifier, generator and prime must be filled in using the gnutls_malloc(). For convenience prime and generator may also be one of the static parameters defined in extra.h.

In case the callback returned a negative number then gnutls will assume that the username does not exist.

In order to prevent attackers from guessing valid usernames, if a user does not exist, g and n values should be filled in using a random user's parameters. In that case the callback must return the special value (1).

The callback function will only be called once per handshake. The callback function should return 0 on success, while -1 indicates an error.

— Function: int gnutls_srp_verifier (const char * username, const char * password, const gnutls_datum_t * salt, const gnutls_datum_t * generator, const gnutls_datum_t * prime, gnutls_datum_t * res)

username: is the user's name

password: is the user's password

salt: should be some randomly generated bytes

generator: is the generator of the group

prime: is the group's prime

res: where the verifier will be stored.

This function will create an SRP verifier, as specified in RFC2945. The prime and generator should be one of the static parameters defined in gnutls/extra.h or may be generated using the GCRYPT functions gcry_prime_generate() and gcry_prime_group_generator(). The verifier will be allocated with malloc and will be stored in res using binary format.

— Function: const char * gnutls_strerror (int error)

error: is an error returned by a gnutls function. Error is always a negative value.

This function is similar to strerror(). Differences: it accepts an error number returned by a gnutls function; In case of an unknown error a descriptive string is sent instead of NULL.

— Function: void gnutls_transport_get_ptr2 (gnutls_session_t session, gnutls_transport_ptr_t * recv_ptr, gnutls_transport_ptr_t * send_ptr)

session: is a gnutls_session_t structure.

recv_ptr: will hold the value for the pull function

send_ptr: will hold the value for the push function

Used to get the arguments of the transport functions (like PUSH and PULL). These should have been set using gnutls_transport_set_ptr2().

— Function: gnutls_transport_ptr_t gnutls_transport_get_ptr (gnutls_session_t session)

session: is a gnutls_session_t structure.

Used to get the first argument of the transport function (like PUSH and PULL). This must have been set using gnutls_transport_set_ptr().

— Function: void gnutls_transport_set_lowat (gnutls_session_t session, int num)

session: is a gnutls_session_t structure.

num: is the low water value.

Used to set the lowat value in order for select to check if there are pending data to socket buffer. Used only if you have changed the default low water value (default is 1). Normally you will not need that function. This function is only useful if using berkeley style sockets. Otherwise it must be called and set lowat to zero.

— Function: void gnutls_transport_set_ptr2 (gnutls_session_t session, gnutls_transport_ptr_t recv_ptr, gnutls_transport_ptr_t send_ptr)

session: is a gnutls_session_t structure.

recv_ptr: is the value for the pull function

send_ptr: is the value for the push function

Used to set the first argument of the transport function (like PUSH and PULL). In berkeley style sockets this function will set the connection handle. With this function you can use two different pointers for receiving and sending.

— Function: void gnutls_transport_set_ptr (gnutls_session_t session, gnutls_transport_ptr_t ptr)

session: is a gnutls_session_t structure.

ptr: is the value.

Used to set the first argument of the transport function (like PUSH and PULL). In berkeley style sockets this function will set the connection handle.

— Function: void gnutls_transport_set_pull_function (gnutls_session_t session, gnutls_pull_func pull_func)

session: gnutls session

pull_func: a callback function similar to read()

This is the function where you set a function for gnutls to receive data. Normally, if you use berkeley style sockets, do not need to use this function since the default (recv(2)) will probably be ok.

PULL_FUNC is of the form, ssize_t (*gnutls_pull_func)(gnutls_transport_ptr_t, void*, size_t);

— Function: void gnutls_transport_set_push_function (gnutls_session_t session, gnutls_push_func push_func)

session: gnutls session

push_func: a callback function similar to write()

This is the function where you set a push function for gnutls to use in order to send data. If you are going to use berkeley style sockets, you do not need to use this function since the default (send(2)) will probably be ok. Otherwise you should specify this function for gnutls to be able to send data.

PUSH_FUNC is of the form, ssize_t (*gnutls_push_func)(gnutls_transport_ptr_t, const void*, size_t);