27ed73a98f
Reviewed-by: Kurt Roeckx <kurt@roeckx.be> Reviewed-by: Rich Salz <rsalz@openssl.org> GH: #1834
108 lines
3.5 KiB
Text
108 lines
3.5 KiB
Text
=pod
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=head1 NAME
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EVP_PKEY_CTX_set_tls1_prf_md,
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EVP_PKEY_CTX_set1_tls1_prf_secret, EVP_PKEY_CTX_add1_tls1_prf_seed -
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TLS PRF key derivation algorithm
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=head1 SYNOPSIS
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#include <openssl/kdf.h>
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int EVP_PKEY_CTX_set_tls1_prf_md(EVP_PKEY_CTX *pctx, const EVP_MD *md);
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int EVP_PKEY_CTX_set1_tls1_prf_secret(EVP_PKEY_CTX *pctx,
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unsigned char *sec, int seclen);
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int EVP_PKEY_CTX_add1_tls1_prf_seed(EVP_PKEY_CTX *pctx,
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unsigned char *seed, int seedlen);
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=head1 DESCRIPTION
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The B<EVP_PKEY_TLS1_PRF> algorithm implements the PRF key derivation function for
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TLS. It has no associated private key and only implements key derivation
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using L<EVP_PKEY_derive(3)>.
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EVP_PKEY_set_tls1_prf_md() sets the message digest associated with the
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TLS PRF. EVP_md5_sha1() is treated as a special case which uses the PRF
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algorithm using both B<MD5> and B<SHA1> as used in TLS 1.0 and 1.1.
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EVP_PKEY_CTX_set_tls1_prf_secret() sets the secret value of the TLS PRF
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to B<seclen> bytes of the buffer B<sec>. Any existing secret value is replaced
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and any seed is reset.
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EVP_PKEY_CTX_add1_tls1_prf_seed() sets the seed to B<seedlen> bytes of B<seed>.
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If a seed is already set it is appended to the existing value.
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=head1 STRING CTRLS
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The TLS PRF also supports string based control operations using
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L<EVP_PKEY_CTX_ctrl_str(3)>.
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The B<type> parameter "md" uses the supplied B<value> as the name of the digest
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algorithm to use.
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The B<type> parameters "secret" and "seed" use the supplied B<value> parameter
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as a secret or seed value.
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The names "hexsecret" and "hexseed" are similar except they take a hex string
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which is converted to binary.
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=head1 NOTES
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All these functions are implemented as macros.
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A context for the TLS PRF can be obtained by calling:
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EVP_PKEY_CTX *pctx = EVP_PKEY_new_id(EVP_PKEY_TLS1_PRF, NULL);
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The digest, secret value and seed must be set before a key is derived or an
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error occurs.
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The total length of all seeds cannot exceed 1024 bytes in length: this should
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be more than enough for any normal use of the TLS PRF.
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The output length of the PRF is specified by the length parameter in the
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EVP_PKEY_derive() function. Since the output length is variable, setting
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the buffer to B<NULL> is not meaningful for the TLS PRF.
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Optimised versions of the TLS PRF can be implemented in an ENGINE.
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=head1 RETURN VALUES
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All these functions return 1 for success and 0 or a negative value for failure.
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In particular a return value of -2 indicates the operation is not supported by
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the public key algorithm.
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=head1 EXAMPLE
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This example derives 10 bytes using SHA-256 with the secret key "secret"
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and seed value "seed":
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EVP_PKEY_CTX *pctx;
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unsigned char out[10];
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size_t outlen = sizeof(out);
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pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_TLS1_PRF, NULL);
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if (EVP_PKEY_derive_init(pctx) <= 0)
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/* Error */
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if (EVP_PKEY_CTX_set_tls1_prf_md(pctx, EVP_sha256()) <= 0)
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/* Error */
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if (EVP_PKEY_CTX_set1_tls1_prf_secret(pctx, "secret", 6) <= 0)
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/* Error */
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if (EVP_PKEY_CTX_add1_tls1_prf_seed(pctx, "seed", 4) <= 0)
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/* Error */
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if (EVP_PKEY_derive(pctx, out, &outlen) <= 0)
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/* Error */
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=head1 SEE ALSO
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L<EVP_PKEY_CTX_new(3)>,
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L<EVP_PKEY_CTX_ctrl_str(3)>,
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L<EVP_PKEY_derive(3)>
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=head1 COPYRIGHT
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Copyright 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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