1=pod 2 3=head1 NAME 4 5EVP_KDF-X963 - The X9.63-2001 EVP_KDF implementation 6 7=head1 DESCRIPTION 8 9The EVP_KDF-X963 algorithm implements the key derivation function (X963KDF). 10X963KDF is used by Cryptographic Message Syntax (CMS) for EC KeyAgreement, to 11derive a key using input such as a shared secret key and shared info. 12 13=head2 Identity 14 15"X963KDF" is the name for this implementation; it 16can be used with the EVP_KDF_fetch() function. 17 18=head2 Supported parameters 19 20The supported parameters are: 21 22=over 4 23 24=item "properties" (B<OSSL_KDF_PARAM_PROPERTIES>) <UTF8 string> 25 26=item "digest" (B<OSSL_KDF_PARAM_DIGEST>) <UTF8 string> 27 28These parameters work as described in L<EVP_KDF(3)/PARAMETERS>. 29 30=item "key" (B<OSSL_KDF_PARAM_KEY>) <octet string> 31 32The shared secret used for key derivation. 33This parameter sets the secret. 34 35=item "info" (B<OSSL_KDF_PARAM_INFO>) <octet string> 36 37This parameter specifies an optional value for shared info. 38 39=back 40 41=head1 NOTES 42 43X963KDF is very similar to the SSKDF that uses a digest as the auxiliary function, 44X963KDF appends the counter to the secret, whereas SSKDF prepends the counter. 45 46A context for X963KDF can be obtained by calling: 47 48 EVP_KDF *kdf = EVP_KDF_fetch(NULL, "X963KDF", NULL); 49 EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf); 50 51The output length of an X963KDF is specified via the I<keylen> 52parameter to the L<EVP_KDF_derive(3)> function. 53 54=head1 EXAMPLES 55 56This example derives 10 bytes, with the secret key "secret" and sharedinfo 57value "label": 58 59 EVP_KDF *kdf; 60 EVP_KDF_CTX *kctx; 61 unsigned char out[10]; 62 OSSL_PARAM params[4], *p = params; 63 64 kdf = EVP_KDF_fetch(NULL, "X963KDF", NULL); 65 kctx = EVP_KDF_CTX_new(kdf); 66 EVP_KDF_free(kdf); 67 68 *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST, 69 SN_sha256, strlen(SN_sha256)); 70 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SECRET, 71 "secret", (size_t)6); 72 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO, 73 "label", (size_t)5); 74 *p = OSSL_PARAM_construct_end(); 75 if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0) { 76 error("EVP_KDF_derive"); 77 } 78 79 EVP_KDF_CTX_free(kctx); 80 81=head1 CONFORMING TO 82 83"SEC 1: Elliptic Curve Cryptography" 84 85=head1 SEE ALSO 86 87L<EVP_KDF(3)>, 88L<EVP_KDF_CTX_new(3)>, 89L<EVP_KDF_CTX_free(3)>, 90L<EVP_KDF_CTX_set_params(3)>, 91L<EVP_KDF_CTX_get_kdf_size(3)>, 92L<EVP_KDF_derive(3)>, 93L<EVP_KDF(3)/PARAMETERS> 94 95=head1 HISTORY 96 97This functionality was added in OpenSSL 3.0. 98 99=head1 COPYRIGHT 100 101Copyright 2019-2021 The OpenSSL Project Authors. All Rights Reserved. 102 103Licensed under the Apache License 2.0 (the "License"). You may not use 104this file except in compliance with the License. You can obtain a copy 105in the file LICENSE in the source distribution or at 106L<https://www.openssl.org/source/license.html>. 107 108=cut 109