b97fdb57a2
Reviewed-by: Rich Salz <rsalz@openssl.org> (Merged from https://github.com/openssl/openssl/pull/1900)
88 lines
3.3 KiB
Text
88 lines
3.3 KiB
Text
=pod
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=head1 NAME
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SSL_get_client_random, SSL_get_server_random, SSL_SESSION_get_master_key - retrieve internal TLS/SSL random values and master key
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=head1 SYNOPSIS
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#include <openssl/ssl.h>
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size_t SSL_get_client_random(const SSL *ssl, unsigned char *out, size_t outlen);
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size_t SSL_get_server_random(const SSL *ssl, unsigned char *out, size_t outlen);
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size_t SSL_SESSION_get_master_key(const SSL_SESSION *session, unsigned char *out, size_t outlen);
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=head1 DESCRIPTION
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SSL_get_client_random() extracts the random value sent from the client
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to the server during the initial SSL/TLS handshake. It copies as many
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bytes as it can of this value into the buffer provided in B<out>,
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which must have at least B<outlen> bytes available. It returns the
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total number of bytes that were actually copied. If B<outlen> is
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zero, SSL_get_client_random() copies nothing, and returns the
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total size of the client_random value.
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SSL_get_server_random() behaves the same, but extracts the random value
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sent from the server to the client during the initial SSL/TLS handshake.
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SSL_SESSION_get_master_key() behaves the same, but extracts the master
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secret used to guarantee the security of the SSL/TLS session. This one
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can be dangerous if misused; see NOTES below.
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=head1 NOTES
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You probably shouldn't use these functions.
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These functions expose internal values from the TLS handshake, for
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use in low-level protocols. You probably should not use them, unless
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you are implementing something that needs access to the internal protocol
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details.
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Despite the names of SSL_get_client_random() and SSL_get_server_random(), they
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ARE NOT random number generators. Instead, they return the mostly-random values that
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were already generated and used in the TLS protocol. Using them
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in place of RAND_bytes() would be grossly foolish.
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The security of your TLS session depends on keeping the master key secret:
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do not expose it, or any information about it, to anybody.
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If you need to calculate another secret value that depends on the master
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secret, you should probably use SSL_export_keying_material() instead, and
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forget that you ever saw these functions.
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In current versions of the TLS protocols, the length of client_random
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(and also server_random) is always SSL3_RANDOM_SIZE bytes. Support for
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other outlen arguments to the SSL_get_*_random() functions is provided
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in case of the unlikely event that a future version or variant of TLS
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uses some other length there.
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Finally, though the "client_random" and "server_random" values are called
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"random", many TLS implementations will generate four bytes of those
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values based on their view of the current time.
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=head1 RETURN VALUES
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If B<outlen> is greater than 0, these functions return the number of bytes
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actually copied, which will be less than or equal to B<outlen>.
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If B<outlen> is 0, these functions return the maximum number
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of bytes they would copy--that is, the length of the underlying field.
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=head1 SEE ALSO
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L<ssl(7)>,
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L<RAND_bytes(3)>,
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L<SSL_export_keying_material(3)>
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=head1 COPYRIGHT
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Copyright 2015-2016 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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