| 1 | =pod
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| 2 |
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| 3 | =head1 NAME
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| 4 |
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| 5 | EVP_KDF-TLS1_PRF - The TLS1 PRF EVP_KDF implementation
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| 6 |
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| 7 | =head1 DESCRIPTION
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| 8 |
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| 9 | Support for computing the B<TLS1> PRF through the B<EVP_KDF> API.
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| 10 |
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| 11 | The EVP_KDF-TLS1_PRF algorithm implements the PRF used by TLS versions up to
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| 12 | and including TLS 1.2.
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| 13 |
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| 14 | =head2 Identity
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| 15 |
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| 16 | "TLS1-PRF" is the name for this implementation; it
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| 17 | can be used with the EVP_KDF_fetch() function.
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| 18 |
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| 19 | =head2 Supported parameters
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| 20 |
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| 21 | The supported parameters are:
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| 22 |
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| 23 | =over 4
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| 24 |
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| 25 | =item "properties" (B<OSSL_KDF_PARAM_PROPERTIES>) <UTF8 string>
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| 26 |
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| 27 | =item "digest" (B<OSSL_KDF_PARAM_DIGEST>) <UTF8 string>
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| 28 |
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| 29 | These parameters work as described in L<EVP_KDF(3)/PARAMETERS>.
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| 30 |
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| 31 | The B<OSSL_KDF_PARAM_DIGEST> parameter is used to set the message digest
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| 32 | associated with the TLS PRF.
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| 33 | EVP_md5_sha1() is treated as a special case which uses the
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| 34 | PRF algorithm using both B<MD5> and B<SHA1> as used in TLS 1.0 and 1.1.
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| 35 |
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| 36 | =item "secret" (B<OSSL_KDF_PARAM_SECRET>) <octet string>
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| 37 |
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| 38 | This parameter sets the secret value of the TLS PRF.
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| 39 | Any existing secret value is replaced.
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| 40 |
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| 41 | =item "seed" (B<OSSL_KDF_PARAM_SEED>) <octet string>
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| 42 |
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| 43 | This parameter sets the context seed.
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| 44 | The length of the context seed cannot exceed 1024 bytes;
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| 45 | this should be more than enough for any normal use of the TLS PRF.
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| 46 |
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| 47 | =back
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| 48 |
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| 49 | =head1 NOTES
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| 50 |
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| 51 | A context for the TLS PRF can be obtained by calling:
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| 52 |
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| 53 | EVP_KDF *kdf = EVP_KDF_fetch(NULL, "TLS1-PRF", NULL);
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| 54 | EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);
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| 55 |
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| 56 | The digest, secret value and seed must be set before a key is derived otherwise
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| 57 | an error will occur.
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| 58 |
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| 59 | The output length of the PRF is specified by the I<keylen> parameter to the
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| 60 | EVP_KDF_derive() function.
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| 61 |
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| 62 | =head1 EXAMPLES
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| 63 |
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| 64 | This example derives 10 bytes using SHA-256 with the secret key "secret"
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| 65 | and seed value "seed":
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| 66 |
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| 67 | EVP_KDF *kdf;
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| 68 | EVP_KDF_CTX *kctx;
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| 69 | unsigned char out[10];
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| 70 | OSSL_PARAM params[4], *p = params;
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| 71 |
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| 72 | kdf = EVP_KDF_fetch(NULL, "TLS1-PRF", NULL);
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| 73 | kctx = EVP_KDF_CTX_new(kdf);
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| 74 | EVP_KDF_free(kdf);
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| 75 |
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| 76 | *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
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| 77 | SN_sha256, strlen(SN_sha256));
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| 78 | *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SECRET,
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| 79 | "secret", (size_t)6);
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| 80 | *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SEED,
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| 81 | "seed", (size_t)4);
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| 82 | *p = OSSL_PARAM_construct_end();
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| 83 | if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0) {
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| 84 | error("EVP_KDF_derive");
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| 85 | }
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| 86 | EVP_KDF_CTX_free(kctx);
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| 87 |
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| 88 | =head1 CONFORMING TO
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| 89 |
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| 90 | RFC 2246, RFC 5246 and NIST SP 800-135 r1
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| 91 |
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| 92 | =head1 SEE ALSO
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| 93 |
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| 94 | L<EVP_KDF(3)>,
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| 95 | L<EVP_KDF_CTX_new(3)>,
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| 96 | L<EVP_KDF_CTX_free(3)>,
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| 97 | L<EVP_KDF_CTX_set_params(3)>,
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| 98 | L<EVP_KDF_derive(3)>,
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| 99 | L<EVP_KDF(3)/PARAMETERS>
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| 100 |
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| 101 | =head1 HISTORY
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| 102 |
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| 103 | This functionality was added in OpenSSL 3.0.
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| 104 |
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| 105 | =head1 COPYRIGHT
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| 106 |
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| 107 | Copyright 2018-2022 The OpenSSL Project Authors. All Rights Reserved.
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| 108 |
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| 109 | Licensed under the Apache License 2.0 (the "License"). You may not use
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| 110 | this file except in compliance with the License. You can obtain a copy
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| 111 | in the file LICENSE in the source distribution or at
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| 112 | L<https://www.openssl.org/source/license.html>.
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| 113 |
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| 114 | =cut
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