1=pod
2
3=head1 NAME
4
5SSL_get_client_random,
6SSL_get_server_random,
7SSL_SESSION_get_master_key,
8SSL_SESSION_set1_master_key
9- get internal TLS/SSL random values and get/set master key
10
11=head1 SYNOPSIS
12
13 #include <openssl/ssl.h>
14
15 size_t SSL_get_client_random(const SSL *ssl, unsigned char *out, size_t outlen);
16 size_t SSL_get_server_random(const SSL *ssl, unsigned char *out, size_t outlen);
17 size_t SSL_SESSION_get_master_key(const SSL_SESSION *session,
18                                   unsigned char *out, size_t outlen);
19 int SSL_SESSION_set1_master_key(SSL_SESSION *sess, const unsigned char *in,
20                                 size_t len);
21
22=head1 DESCRIPTION
23
24SSL_get_client_random() extracts the random value sent from the client
25to the server during the initial SSL/TLS handshake.  It copies as many
26bytes as it can of this value into the buffer provided in B<out>,
27which must have at least B<outlen> bytes available. It returns the
28total number of bytes that were actually copied.  If B<outlen> is
29zero, SSL_get_client_random() copies nothing, and returns the
30total size of the client_random value.
31
32SSL_get_server_random() behaves the same, but extracts the random value
33sent from the server to the client during the initial SSL/TLS handshake.
34
35SSL_SESSION_get_master_key() behaves the same, but extracts the master
36secret used to guarantee the security of the SSL/TLS session.  This one
37can be dangerous if misused; see NOTES below.
38
39SSL_SESSION_set1_master_key() sets the master key value associated with the
40SSL_SESSION B<sess>. For example, this could be used to set up a session based
41PSK (see L<SSL_CTX_set_psk_use_session_callback(3)>). The master key of length
42B<len> should be provided at B<in>. The supplied master key is copied by the
43function, so the caller is responsible for freeing and cleaning any memory
44associated with B<in>. The caller must ensure that the length of the key is
45suitable for the ciphersuite associated with the SSL_SESSION.
46
47=head1 NOTES
48
49You probably shouldn't use these functions.
50
51These functions expose internal values from the TLS handshake, for
52use in low-level protocols.  You probably should not use them, unless
53you are implementing something that needs access to the internal protocol
54details.
55
56Despite the names of SSL_get_client_random() and SSL_get_server_random(), they
57ARE NOT random number generators.  Instead, they return the mostly-random values that
58were already generated and used in the TLS protocol.  Using them
59in place of RAND_bytes() would be grossly foolish.
60
61The security of your TLS session depends on keeping the master key secret:
62do not expose it, or any information about it, to anybody.
63If you need to calculate another secret value that depends on the master
64secret, you should probably use SSL_export_keying_material() instead, and
65forget that you ever saw these functions.
66
67In current versions of the TLS protocols, the length of client_random
68(and also server_random) is always SSL3_RANDOM_SIZE bytes. Support for
69other outlen arguments to the SSL_get_*_random() functions is provided
70in case of the unlikely event that a future version or variant of TLS
71uses some other length there.
72
73Finally, though the "client_random" and "server_random" values are called
74"random", many TLS implementations will generate four bytes of those
75values based on their view of the current time.
76
77
78=head1 RETURN VALUES
79
80SSL_SESSION_set1_master_key() returns 1 on success or 0 on failure.
81
82For the other functions, if B<outlen> is greater than 0 then these functions
83return the number of bytes actually copied, which will be less than or equal to
84B<outlen>. If B<outlen> is 0 then these functions return the maximum number
85of bytes they would copy -- that is, the length of the underlying field.
86
87=head1 SEE ALSO
88
89L<ssl(7)>,
90L<RAND_bytes(3)>,
91L<SSL_export_keying_material(3)>,
92L<SSL_CTX_set_psk_use_session_callback(3)>
93
94
95=head1 COPYRIGHT
96
97Copyright 2015-2017 The OpenSSL Project Authors. All Rights Reserved.
98
99Licensed under the OpenSSL license (the "License").  You may not use
100this file except in compliance with the License.  You can obtain a copy
101in the file LICENSE in the source distribution or at
102L<https://www.openssl.org/source/license.html>.
103
104=cut
105