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105 lines
4.1 KiB
Plaintext
105 lines
4.1 KiB
Plaintext
=pod
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=head1 NAME
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SSL_get_client_random,
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SSL_get_server_random,
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SSL_SESSION_get_master_key,
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SSL_SESSION_set1_master_key
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- get internal TLS/SSL random values and get/set 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,
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unsigned char *out, size_t outlen);
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int SSL_SESSION_set1_master_key(SSL_SESSION *sess, const unsigned char *in,
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size_t len);
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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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SSL_SESSION_set1_master_key() sets the master key value associated with the
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SSL_SESSION B<sess>. For example, this could be used to set up a session based
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PSK (see L<SSL_CTX_set_psk_use_session_callback(3)>). The master key of length
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B<len> should be provided at B<in>. The supplied master key is copied by the
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function, so the caller is responsible for freeing and cleaning any memory
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associated with B<in>. The caller must ensure that the length of the key is
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suitable for the ciphersuite associated with the SSL_SESSION.
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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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SSL_SESSION_set1_master_key() returns 1 on success or 0 on failure.
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For the other functions, if B<outlen> is greater than 0 then these functions
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return the number of bytes actually copied, which will be less than or equal to
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B<outlen>. If B<outlen> is 0 then 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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L<SSL_CTX_set_psk_use_session_callback(3)>
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=head1 COPYRIGHT
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Copyright 2015-2017 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (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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