1=pod 2 3=head1 NAME 4 5EVP_KDF-TLS13_KDF - The TLS 1.3 EVP_KDF implementation 6 7=head1 DESCRIPTION 8 9Support for computing the TLS 1.3 version of the B<HKDF> KDF through 10the B<EVP_KDF> API. 11 12The EVP_KDF-TLS13_KDF algorithm implements the HKDF key derivation function 13as used by TLS 1.3. 14 15=head2 Identity 16 17"TLS13-KDF" is the name for this implementation; it 18can be used with the EVP_KDF_fetch() function. 19 20=head2 Supported parameters 21 22The supported parameters are: 23 24=over 4 25 26=item "properties" (B<OSSL_KDF_PARAM_PROPERTIES>) <UTF8 string> 27 28=item "digest" (B<OSSL_KDF_PARAM_DIGEST>) <UTF8 string> 29 30=item "key" (B<OSSL_KDF_PARAM_KEY>) <octet string> 31 32=item "salt" (B<OSSL_KDF_PARAM_SALT>) <octet string> 33 34These parameters work as described in L<EVP_KDF(3)/PARAMETERS>. 35 36=item "prefix" (B<OSSL_KDF_PARAM_PREFIX>) <octet string> 37 38This parameter sets the label prefix on the specified TLS 1.3 KDF context. 39For TLS 1.3 this should be set to the ASCII string "tls13 " without a 40trailing zero byte. Refer to RFC 8446 section 7.1 "Key Schedule" for details. 41 42=item "label" (B<OSSL_KDF_PARAM_LABEL>) <octet string> 43 44This parameter sets the label on the specified TLS 1.3 KDF context. 45Refer to RFC 8446 section 7.1 "Key Schedule" for details. 46 47=item "data" (B<OSSL_KDF_PARAM_DATA>) <octet string> 48 49This parameter sets the context data on the specified TLS 1.3 KDF context. 50Refer to RFC 8446 section 7.1 "Key Schedule" for details. 51 52=item "mode" (B<OSSL_KDF_PARAM_MODE>) <UTF8 string> or <integer> 53 54This parameter sets the mode for the TLS 1.3 KDF operation. 55There are two modes that are currently defined: 56 57=over 4 58 59=item "EXTRACT_ONLY" or B<EVP_KDF_HKDF_MODE_EXTRACT_ONLY> 60 61In this mode calling L<EVP_KDF_derive(3)> will just perform the extract 62operation. The value returned will be the intermediate fixed-length pseudorandom 63key K. The I<keylen> parameter must match the size of K, which can be looked 64up by calling EVP_KDF_CTX_get_kdf_size() after setting the mode and digest. 65 66The digest, key and salt values must be set before a key is derived otherwise 67an error will occur. 68 69=item "EXPAND_ONLY" or B<EVP_KDF_HKDF_MODE_EXPAND_ONLY> 70 71In this mode calling L<EVP_KDF_derive(3)> will just perform the expand 72operation. The input key should be set to the intermediate fixed-length 73pseudorandom key K returned from a previous extract operation. 74 75The digest, key and info values must be set before a key is derived otherwise 76an error will occur. 77 78=back 79 80=back 81 82The OpenSSL FIPS provider also supports the following parameters: 83 84=over 4 85 86=item "fips-indicator" (B<OSSL_KDF_PARAM_FIPS_APPROVED_INDICATOR>) <integer> 87 88A getter that returns 1 if the operation is FIPS approved, or 0 otherwise. 89This may be used after calling EVP_KDF_derive. It returns 0 if any "***-check" 90related parameter is set to 0 and the check fails. 91 92=item "digest-check" (B<OSSL_KDF_PARAM_FIPS_DIGEST_CHECK>) <integer> 93 94The default value of 1 causes an error during EVP_KDF_CTX_set_params() if 95used digest is not approved. 96Setting this to zero will ignore the error and set the approved 97"fips-indicator" to 0. 98This option breaks FIPS compliance if it causes the approved "fips-indicator" 99to return 0. 100 101According to RFC 8446, the following are approved digest algorithms: SHA2-256, 102SHA2-384. 103 104=item "key-check" (B<OSSL_KDF_PARAM_FIPS_KEY_CHECK>) <integer> 105 106The default value of 1 causes an error during EVP_KDF_CTX_set_params() if the 107length of used key-derivation key (B<OSSL_KDF_PARAM_KEY>) is shorter than 112 108bits. 109Setting this to zero will ignore the error and set the approved 110"fips-indicator" to 0. 111This option breaks FIPS compliance if it causes the approved "fips-indicator" 112to return 0. 113 114=back 115 116=head1 NOTES 117 118This KDF is intended for use by the TLS 1.3 implementation in libssl. 119It does not support all the options and capabilities that HKDF does. 120 121The I<OSSL_PARAM> array passed to L<EVP_KDF_derive(3)> or 122L<EVP_KDF_CTX_set_params(3)> must specify all of the parameters required. 123This KDF does not support a piecemeal approach to providing these. 124 125A context for a TLS 1.3 KDF can be obtained by calling: 126 127 EVP_KDF *kdf = EVP_KDF_fetch(NULL, "TLS13-KDF", NULL); 128 EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf); 129 130The output length of a TLS 1.3 KDF expand operation is specified via the 131I<keylen> parameter to the L<EVP_KDF_derive(3)> function. When using 132EVP_KDF_HKDF_MODE_EXTRACT_ONLY the I<keylen> parameter must equal the size of 133the intermediate fixed-length pseudorandom key otherwise an error will occur. 134For that mode, the fixed output size can be looked up by calling 135EVP_KDF_CTX_get_kdf_size() after setting the mode and digest on the 136B<EVP_KDF_CTX>. 137 138=head1 CONFORMING TO 139 140RFC 8446 141 142=head1 SEE ALSO 143 144L<EVP_KDF(3)>, 145L<EVP_KDF_CTX_new(3)>, 146L<EVP_KDF_CTX_free(3)>, 147L<EVP_KDF_CTX_get_kdf_size(3)>, 148L<EVP_KDF_CTX_set_params(3)>, 149L<EVP_KDF_derive(3)>, 150L<EVP_KDF(3)/PARAMETERS>, 151L<EVP_KDF-HKDF(7)> 152 153=head1 HISTORY 154 155This functionality was added in OpenSSL 3.0. 156 157=head1 COPYRIGHT 158 159Copyright 2021-2024 The OpenSSL Project Authors. All Rights Reserved. 160 161Licensed under the Apache License 2.0 (the "License"). You may not use 162this file except in compliance with the License. You can obtain a copy 163in the file LICENSE in the source distribution or at 164L<https://www.openssl.org/source/license.html>. 165 166=cut 167
