=pod =head1 NAME SSL_get_client_random, SSL_get_server_random, SSL_SESSION_get_master_key - retrieve internal TLS/SSL random values and master key =head1 SYNOPSIS #include size_t SSL_get_client_random(const SSL *ssl, unsigned char *out, size_t outlen); size_t SSL_get_server_random(const SSL *ssl, unsigned char *out, size_t outlen); size_t SSL_SESSION_get_master_key(const SSL_SESSION *session, unsigned char *out, size_t outlen); =head1 DESCRIPTION SSL_get_client_random() extracts the random value sent from the client to the server during the initial SSL/TLS handshake. It copies as many bytes as it can of this value into the buffer provided in B, which must have at least B bytes available. It returns the total number of bytes that were actually copied. If B is zero, SSL_get_client_random() copies nothing, and returns the total size of the client_random value. SSL_get_server_random() behaves the same, but extracts the random value sent from the server to the client during the initial SSL/TLS handshake. SSL_SESSION_get_master_key() behaves the same, but extracts the master secret used to guarantee the security of the SSL/TLS session. This one can be dangerous if misused; see NOTES below. =head1 NOTES You probably shouldn't use these functions. These functions expose internal values from the TLS handshake, for use in low-level protocols. You probably should not use them, unless you are implementing something that needs access to the internal protocol details. Despite the names of SSL_get_client_random() and SSL_get_server_random(), they ARE NOT random number generators. Instead, they return the mostly-random values that were already generated and used in the TLS protocol. Using them in place of RAND_bytes() would be grossly foolish. The security of your TLS session depends on keeping the master key secret: do not expose it, or any information about it, to anybody. If you need to calculate another secret value that depends on the master secret, you should probably use SSL_export_keying_material() instead, and forget that you ever saw these functions. In current versions of the TLS protocols, the length of client_random (and also server_random) is always SSL3_RANDOM_SIZE bytes. Support for other outlen arguments to the SSL_get_*_random() functions is provided in case of the unlikely event that a future version or variant of TLS uses some other length there. Finally, though the "client_random" and "server_random" values are called "random", many TLS implementations will generate four bytes of those values based on their view of the current time. =head1 RETURN VALUES If B is greater than 0, these functions return the number of bytes actually copied, which will be less than or equal to B. If B is 0, these functions return the maximum number of bytes they would copy--that is, the length of the underlying field. =head1 SEE ALSO L, L, L =head1 COPYRIGHT Copyright 2015-2016 The OpenSSL Project Authors. All Rights Reserved. Licensed under the OpenSSL license (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at L. =cut