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      1 =pod
      2 
      3 =head1 NAME
      4 
      5 EVP_KDF-X963 - The X9.63-2001 EVP_KDF implementation
      6 
      7 =head1 DESCRIPTION
      8 
      9 The EVP_KDF-X963 algorithm implements the key derivation function (X963KDF).
     10 X963KDF is used by Cryptographic Message Syntax (CMS) for EC KeyAgreement, to
     11 derive a key using input such as a shared secret key and shared info.
     12 
     13 The output is considered to be keying material.
     14 
     15 =head2 Identity
     16 
     17 "X963KDF" is the name for this implementation; it
     18 can be used with the EVP_KDF_fetch() function.
     19 
     20 =head2 Supported parameters
     21 
     22 The 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 These parameters work as described in L<EVP_KDF(3)/PARAMETERS>.
     31 
     32 =item "key" (B<OSSL_KDF_PARAM_KEY>) <octet string>
     33 
     34 The shared secret used for key derivation.
     35 This parameter sets the secret.
     36 
     37 =item "info" (B<OSSL_KDF_PARAM_INFO>) <octet string>
     38 
     39 This parameter specifies an optional value for shared info.
     40 
     41 =back
     42 
     43 The OpenSSL FIPS provider also supports the following parameters:
     44 
     45 =over 4
     46 
     47 =item "fips-indicator" (B<OSSL_KDF_PARAM_FIPS_APPROVED_INDICATOR>) <integer>
     48 
     49 A getter that returns 1 if the operation is FIPS approved, or 0 otherwise.
     50 This may be used after calling EVP_KDF_derive. It returns 0 if any "***-check"
     51 related parameter is set to 0 and the check fails.
     52 
     53 =item "digest-check" (B<OSSL_KDF_PARAM_FIPS_DIGEST_CHECK>) <int>
     54 
     55 The default value of 1 causes an error during EVP_KDF_CTX_set_params() if
     56 used digest is not approved.
     57 Setting this to zero will ignore the error and set the approved
     58 "fips-indicator" to 0.
     59 This option breaks FIPS compliance if it causes the approved "fips-indicator"
     60 to return 0.
     61 
     62 According to ANSI X9.63-2001, the following are approved digest algorithms:
     63 SHA2-224, SHA2-256, SHA2-384, SHA2-512, SHA2-512/224, SHA2-512/256, SHA3-224,
     64 SHA3-256, SHA3-384, SHA3-512.
     65 
     66 =item "key-check" (B<OSSL_KDF_PARAM_FIPS_KEY_CHECK>) <integer>
     67 
     68 The default value of 1 causes an error during EVP_KDF_CTX_set_params() if the
     69 length of used key-derivation key (B<OSSL_KDF_PARAM_KEY>) is shorter than 112
     70 bits.
     71 Setting this to zero will ignore the error and set the approved
     72 "fips-indicator" to 0.
     73 This option breaks FIPS compliance if it causes the approved "fips-indicator"
     74 to return 0.
     75 
     76 =back
     77 
     78 =head1 NOTES
     79 
     80 X963KDF is very similar to the SSKDF that uses a digest as the auxiliary function,
     81 X963KDF appends the counter to the secret, whereas SSKDF prepends the counter.
     82 
     83 A context for X963KDF can be obtained by calling:
     84 
     85  EVP_KDF *kdf = EVP_KDF_fetch(NULL, "X963KDF", NULL);
     86  EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);
     87 
     88 The output length of an X963KDF is specified via the I<keylen>
     89 parameter to the L<EVP_KDF_derive(3)> function.
     90 
     91 =head1 EXAMPLES
     92 
     93 This example derives 10 bytes, with the secret key "secret" and sharedinfo
     94 value "label":
     95 
     96  EVP_KDF *kdf;
     97  EVP_KDF_CTX *kctx;
     98  unsigned char out[10];
     99  OSSL_PARAM params[4], *p = params;
    100 
    101  kdf = EVP_KDF_fetch(NULL, "X963KDF", NULL);
    102  kctx = EVP_KDF_CTX_new(kdf);
    103  EVP_KDF_free(kdf);
    104 
    105  *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
    106                                          SN_sha256, strlen(SN_sha256));
    107  *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SECRET,
    108                                           "secret", (size_t)6);
    109  *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
    110                                           "label", (size_t)5);
    111  *p = OSSL_PARAM_construct_end();
    112  if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0) {
    113      error("EVP_KDF_derive");
    114  }
    115 
    116  EVP_KDF_CTX_free(kctx);
    117 
    118 =head1 CONFORMING TO
    119 
    120 "SEC 1: Elliptic Curve Cryptography"
    121 
    122 =head1 SEE ALSO
    123 
    124 L<EVP_KDF(3)>,
    125 L<EVP_KDF_CTX_new(3)>,
    126 L<EVP_KDF_CTX_free(3)>,
    127 L<EVP_KDF_CTX_set_params(3)>,
    128 L<EVP_KDF_CTX_get_kdf_size(3)>,
    129 L<EVP_KDF_derive(3)>,
    130 L<EVP_KDF(3)/PARAMETERS>
    131 
    132 =head1 HISTORY
    133 
    134 This functionality was added in OpenSSL 3.0.
    135 
    136 =head1 COPYRIGHT
    137 
    138 Copyright 2019-2024 The OpenSSL Project Authors. All Rights Reserved.
    139 
    140 Licensed under the Apache License 2.0 (the "License").  You may not use
    141 this file except in compliance with the License.  You can obtain a copy
    142 in the file LICENSE in the source distribution or at
    143 L<https://www.openssl.org/source/license.html>.
    144 
    145 =cut
    146