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gnutls_srp_set_server_fake_salt_seed(3) gnutls gnutls_srp_set_server_fake_salt_seed(3)


gnutls_srp_set_server_fake_salt_seed - API function


#include <gnutls/gnutls.h>

void gnutls_srp_set_server_fake_salt_seed(gnutls_srp_server_credentials_t cred, const gnutls_datum_t * seed, unsigned int salt_length);


is a gnutls_srp_server_credentials_t type
is the seed data, only needs to be valid until the function returns; size of the seed must be greater than zero
is the length of the generated fake salts


This function sets the seed that is used to generate salts for invalid (non-existent) usernames.

In order to prevent attackers from guessing valid usernames, when a user does not exist gnutls generates a salt and a verifier and proceeds with the protocol as usual. The authentication will ultimately fail, but the client cannot tell whether the username is valid (exists) or invalid.

If an attacker learns the seed, given a salt (which is part of the handshake) which was generated when the seed was in use, it can tell whether or not the authentication failed because of an unknown username. This seed cannot be used to reveal application data or passwords.

salt_length should represent the salt length your application uses. Generating fake salts longer than 20 bytes is not supported.

By default the seed is a random value, different each time a gnutls_srp_server_credentials_t is allocated and fake salts are 16 bytes long.




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3.7.1 gnutls