doc/man7/EVP_KDF-SS.pod

   1 =pod
   2
   3 =head1 NAME
   4
   5 EVP_KDF-SS - The Single Step / One Step EVP_KDF implementation
   6
   7 =head1 DESCRIPTION
   8
   9 The EVP_KDF-SS algorithm implements the Single Step key derivation function (SSKDF).
  10 SSKDF derives a key using input such as a shared secret key (that was generated
  11 during the execution of a key establishment scheme) and fixedinfo.
  12 SSKDF is also informally referred to as 'Concat KDF'.
  13
  14 =head2 Auxiliary function
  15
  16 The implementation uses a selectable auxiliary function H, which can be one of:
  17
  18 =over 4
  19
  20 =item B<H(x) = hash(x, digest=md)>
  21
  22 =item B<H(x) = HMAC_hash(x, key=salt, digest=md)>
  23
  24 =item B<H(x) = KMACxxx(x, key=salt, custom="KDF", outlen=mac_size)>
  25
  26 =back
  27
  28 Both the HMAC and KMAC implementations set the key using the 'salt' value.
  29 The hash and HMAC also require the digest to be set.
  30
  31 =head2 Identity
  32
  33 "SSKDF" is the name for this implementation; it
  34 can be used with the EVP_KDF_fetch() function.
  35
  36 =head2 Supported parameters
  37
  38 The supported parameters are:
  39
  40 =over 4
  41
  42 =item "properties" (B<OSSL_KDF_PARAM_PROPERTIES>) <UTF8 string>
  43
  44 =item "digest" (B<OSSL_KDF_PARAM_DIGEST>) <UTF8 string>
  45
  46 This parameter is ignored for KMAC.
  47
  48 =item "mac" (B<OSSL_KDF_PARAM_MAC>) <UTF8 string>
  49
  50 =item "maclen" (B<OSSL_KDF_PARAM_MAC_SIZE>) <unsigned integer>
  51
  52 =item "salt" (B<OSSL_KDF_PARAM_SALT>) <octet string>
  53
  54 These parameters work as described in L<EVP_KDF(3)/PARAMETERS>.
  55
  56 =item "key" (B<EVP_KDF_CTRL_SET_KEY>) <octet string>
  57
  58 This parameter set the shared secret that is used for key derivation.
  59
  60 =item "info" (B<OSSL_KDF_PARAM_INFO>) <octet string>
  61
  62 This parameter sets an optional value for fixedinfo, also known as otherinfo.
  63
  64 =back
  65
  66 =head1 NOTES
  67
  68 A context for SSKDF can be obtained by calling:
  69
  70  EVP_KDF *kdf = EVP_KDF_fetch(NULL, "SSKDF", NULL);
  71  EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);
  72
  73 The output length of an SSKDF is specified via the I<keylen>
  74 parameter to the L<EVP_KDF_derive(3)> function.
  75
  76 =head1 EXAMPLES
  77
  78 This example derives 10 bytes using H(x) = SHA-256, with the secret key "secret"
  79 and fixedinfo value "label":
  80
  81  EVP_KDF *kdf;
  82  EVP_KDF_CTX *kctx;
  83  unsigned char out[10];
  84  OSSL_PARAM params[4], *p = params;
  85
  86  kdf = EVP_KDF_fetch(NULL, "SSKDF", NULL);
  87  kctx = EVP_KDF_CTX_new(kdf);
  88  EVP_KDF_free(kdf);
  89
  90  *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
  91                                          SN_sha256, strlen(SN_sha256));
  92  *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
  93                                           "secret", (size_t)6);
  94  *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
  95                                           "label", (size_t)5);
  96  *p = OSSL_PARAM_construct_end();
  97  if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0) {
  98      error("EVP_KDF_derive");
  99  }
 100
 101  EVP_KDF_CTX_free(kctx);
 102
 103 This example derives 10 bytes using H(x) = HMAC(SHA-256), with the secret key "secret",
 104 fixedinfo value "label" and salt "salt":
 105
 106  EVP_KDF *kdf;
 107  EVP_KDF_CTX *kctx;
 108  unsigned char out[10];
 109  OSSL_PARAM params[6], *p = params;
 110
 111  kdf = EVP_KDF_fetch(NULL, "SSKDF", NULL);
 112  kctx = EVP_KDF_CTX_new(kdf);
 113  EVP_KDF_free(kdf);
 114
 115  *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC,
 116                                          SN_hmac, strlen(SN_hmac));
 117  *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
 118                                          SN_sha256, strlen(SN_sha256));
 119  *p++ = OSSL_PARAM_construct_octet_string(EVP_KDF_CTRL_SET_KEY,
 120                                           "secret", (size_t)6);
 121  *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
 122                                           "label", (size_t)5);
 123  *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
 124                                           "salt", (size_t)4);
 125  *p = OSSL_PARAM_construct_end();
 126  if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0) {
 127      error("EVP_KDF_derive");
 128  }
 129
 130  EVP_KDF_CTX_free(kctx);
 131
 132 This example derives 10 bytes using H(x) = KMAC128(x,salt,outlen), with the secret key "secret"
 133 fixedinfo value "label", salt of "salt" and KMAC outlen of 20:
 134
 135  EVP_KDF *kdf;
 136  EVP_KDF_CTX *kctx;
 137  unsigned char out[10];
 138  OSSL_PARAM params[6], *p = params;
 139
 140  kdf = EVP_KDF_fetch(NULL, "SSKDF", NULL);
 141  kctx = EVP_KDF_CTX_new(kdf);
 142  EVP_KDF_free(kdf);
 143
 144  *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC,
 145                                          SN_kmac128, strlen(SN_kmac128));
 146  *p++ = OSSL_PARAM_construct_octet_string(EVP_KDF_CTRL_SET_KEY,
 147                                           "secret", (size_t)6);
 148  *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
 149                                           "label", (size_t)5);
 150  *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
 151                                           "salt", (size_t)4);
 152  *p++ = OSSL_PARAM_construct_size_t(OSSL_KDF_PARAM_MAC_SIZE, (size_t)20);
 153  *p = OSSL_PARAM_construct_end();
 154  if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0) {
 155      error("EVP_KDF_derive");
 156  }
 157
 158  EVP_KDF_CTX_free(kctx);
 159
 160 =head1 CONFORMING TO
 161
 162 NIST SP800-56Cr1.
 163
 164 =head1 SEE ALSO
 165
 166 L<EVP_KDF(3)>,
 167 L<EVP_KDF_CTX_new(3)>,
 168 L<EVP_KDF_CTX_free(3)>,
 169 L<EVP_KDF_CTX_set_params(3)>,
 170 L<EVP_KDF_CTX_get_kdf_size(3)>,
 171 L<EVP_KDF_derive(3)>,
 172 L<EVP_KDF(3)/PARAMETERS>
 173
 174 =head1 HISTORY
 175
 176 This functionality was added in OpenSSL 3.0.
 177
 178 =head1 COPYRIGHT
 179
 180 Copyright 2019-2021 The OpenSSL Project Authors. All Rights Reserved.  Copyright
 181 (c) 2019, Oracle and/or its affiliates.  All rights reserved.
 182
 183 Licensed under the Apache License 2.0 (the "License").  You may not use
 184 this file except in compliance with the License.  You can obtain a copy
 185 in the file LICENSE in the source distribution or at
 186 L<https://www.openssl.org/source/license.html>.
 187
 188 =cut