Update KDF documentation (section 7)

[oweals/openssl.git] / doc / man7 / EVP_KDF-TLS1_PRF.pod

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+=pod
+
+=head1 NAME
+
+EVP_KDF-TLS1_PRF - The TLS1 PRF EVP_KDF implementation
+
+=head1 DESCRIPTION
+
+Support for computing the B<TLS1> PRF through the B<EVP_KDF> API.
+
+The EVP_KDF-TLS1_PRF algorithm implements the PRF used by TLS versions up to
+and including TLS 1.2.
+
+=head2 Identity
+
+"TLS1-PRF" is the name for this implementation; it
+can be used with the EVP_KDF_fetch() function.
+
+=head2 Supported parameters
+
+The supported parameters are:
+
+=over 4
+
+=item B<OSSL_KDF_PARAM_PROPERTIES> ("properties") <UTF8 string>
+
+=item B<OSSL_KDF_PARAM_DIGEST> ("digest") <UTF8 string>
+
+These parameters work as described in L<EVP_KDF(3)/PARAMETERS>.
+
+The C<OSSL_KDF_PARAM_DIGEST> parameter is used to set the message digest
+associated with the TLS PRF.
+EVP_md5_sha1() is treated as a special case which uses the
+PRF algorithm using both B<MD5> and B<SHA1> as used in TLS 1.0 and 1.1.
+
+=item B<OSSL_KDF_PARAM_SECRET> ("secret") <octet string>
+
+This parameter sets the secret value of the TLS PRF.
+Any existing secret value is replaced.
+
+=item B<OSSL_KDF_PARAM_SEED> ("seed") <octet string>
+
+This parameter sets the context seed.
+The length of the context seed cannot exceed 1024 bytes;
+this should be more than enough for any normal use of the TLS PRF.
+
+=back
+
+=head1 NOTES
+
+A context for the TLS PRF can be obtained by calling:
+
+ EVP_KDF *kdf = EVP_KDF_fetch(NULL, "TLS1-PRF", NULL);
+ EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);
+
+The digest, secret value and seed must be set before a key is derived otherwise
+an error will occur.
+
+The output length of the PRF is specified by the C<keylen> parameter to the
+EVP_KDF_derive() function.
+
+=head1 EXAMPLES
+
+This example derives 10 bytes using SHA-256 with the secret key "secret"
+and seed value "seed":
+
+ EVP_KDF *kdf;
+ EVP_KDF_CTX *kctx;
+ unsigned char out[10];
+ OSSL_PARAM params[4], *p = params;
+
+ kdf = EVP_KDF_fetch(NULL, "TLS1-PRF", NULL);
+ kctx = EVP_KDF_CTX_new(kdf);
+ EVP_KDF_free(kdf);
+
+ *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
+                                         SN_sha256, strlen(SN_sha256));
+ *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SECRET,
+                                          "secret", (size_t)6);
+ *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SEED,
+                                          "seed", (size_t)4);
+ *p = OSSL_PARAM_construct_end();
+ if (EVP_KDF_set_params(kctx, params) <= 0) {
+     error("EVP_KDF_set_params");
+ }
+ if (EVP_KDF_derive(kctx, out, sizeof(out)) <= 0) {
+     error("EVP_KDF_derive");
+ }
+ EVP_KDF_CTX_free(kctx);
+
+=head1 CONFORMING TO
+
+RFC 2246, RFC 5246 and NIST SP 800-135 r1
+
+=head1 SEE ALSO
+
+L<EVP_KDF>,
+L<EVP_KDF-CTX_new_id(3)>,
+L<EVP_KDF-CTX_free(3)>,
+L<EVP_KDF-ctrl(3)>,
+L<EVP_KDF-derive(3)>,
+L<EVP_KDF-CTX(3)/PARAMETERS>
+
+=head1 COPYRIGHT
+
+Copyright 2018-2019 The OpenSSL Project Authors. All Rights Reserved.
+
+Licensed under the Apache License 2.0 (the "License").  You may not use
+this file except in compliance with the License.  You can obtain a copy
+in the file LICENSE in the source distribution or at
+L<https://www.openssl.org/source/license.html>.
+
+=cut