doc/man7/EVP_KDF-KB.pod

   1 =pod
   2
   3 =head1 NAME
   4
   5 EVP_KDF-KB - The Key-Based EVP_KDF implementation
   6
   7 =head1 DESCRIPTION
   8
   9 The EVP_KDF-KB algorithm implements the Key-Based key derivation function
  10 (KBKDF).  KBKDF derives a key from repeated application of a keyed MAC to an
  11 input secret (and other optional values).
  12
  13 =head2 Identity
  14
  15 "KBKDF" is the name for this implementation; it can be used with the
  16 EVP_KDF_fetch() function.
  17
  18 =head2 Supported parameters
  19
  20 The supported parameters are:
  21
  22 =over 4
  23
  24 =item B<OSSL_KDF_PARAM_PROPERTIES> ("properties") <UTF8 string>
  25
  26 =item B<OSSL_KDF_PARAM_DIGEST> ("digest") <UTF8 string>
  27
  28 =item B<OSSL_KDF_PARAM_DIGEST> ("mac") <UTF8 string>
  29
  30 =item B<OSSL_KDF_PARAM_KEY> ("key") <octet string>
  31
  32 =item B<OSSL_KDF_PARAM_SALT> ("salt") <octet string>
  33
  34 =item B<OSSL_KDF_PARAM_INFO> ("info") <octet string>
  35
  36 =back
  37
  38 The parameters key, salt, and info correspond to KI, Label, and Context
  39 (respectively) in SP800-108.  As in that document, salt and info are optional
  40 and may be omitted.  Currently, only HMAC is supported for mac.
  41
  42 =head1 NOTES
  43
  44 A context for KBKDF can be obtained by calling:
  45
  46  EVP_KDF *kdf = EVP_KDF_fetch(NULL, "KBKDF", NULL);
  47  EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);
  48
  49 The output length of an KBKDF is specified via the C<keylen>
  50 parameter to the L<EVP_KDF_derive(3)> function.
  51
  52 Note that currently OpenSSL only implements Counter mode with HMAC.  Other
  53 variants may be supported in the future.
  54
  55 =head1 EXAMPLES
  56
  57 This example derives 10 bytes using COUNTER-HMAC-SHA256, with KI "secret",
  58 Label "label", and Context "context".
  59
  60  EVP_KDF *kdf;
  61  EVP_KDF_CTX *kctx;
  62  unsigned char out[10];
  63  OSSL_PARAM params[6], *p = params;
  64
  65  kdf = EVP_KDF_fetch(NULL, "KBKDF", NULL);
  66  kctx = EVP_KDF_CTX_new(kdf);
  67  EVP_KDF_free(kdf);
  68
  69  *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
  70                                          "SHA256", 0);
  71  *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC,
  72                                          "HMAC", 0);
  73  *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
  74                                           "secret", strlen("secret"))
  75  *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
  76                                           "context", strlen("context"));
  77  *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
  78                                           "label", strlen("label"));
  79  *p = OSSL_PARAM_construct_end();
  80  if (EVP_KDF_CTX_set_params(kctx, params) <= 0)
  81      error("EVP_KDF_CTX_set_params");
  82  else if (EVP_KDF_derive(kctx, out, sizeof(out)) <= 0)
  83      error("EVP_KDF_derive");
  84
  85  EVP_KDF_CTX_free(kctx);
  86
  87 =head1 CONFORMING TO
  88
  89 NIST SP800-108, IETF RFC 8009.
  90
  91 =head1 SEE ALSO
  92
  93 L<EVP_KDF(3)>,
  94 L<EVP_KDF_CTX_new_id(3)>,
  95 L<EVP_KDF_CTX_free(3)>,
  96 L<EVP_KDF_ctrl(3)>,
  97 L<EVP_KDF_size(3)>,
  98 L<EVP_KDF_derive(3)>,
  99 L<EVP_KDF(3)/PARAMETERS>
 100
 101 =head1 HISTORY
 102
 103 This functionality was added to OpenSSL 3.0.
 104
 105 =head1 COPYRIGHT
 106
 107 Copyright 2019 The OpenSSL Project Authors. All Rights Reserved.
 108 Copyright 2019 Red Hat, Inc.
 109
 110 Licensed under the Apache License 2.0 (the "License").  You may not use
 111 this file except in compliance with the License.  You can obtain a copy
 112 in the file LICENSE in the source distribution or at
 113 L<https://www.openssl.org/source/license.html>.
 114
 115 =cut