EVP_KDF-SS

Section: OpenSSL (7SSL)
Updated: 2024-03-03
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NAME

EVP_KDF-SS - The Single Step / One Step EVP_KDF implementation

DESCRIPTION

The EVP_KDF-SS algorithm implements the Single Step key derivation function (SSKDF). SSKDF derives a key using input such as a shared secret key (that was generated during the execution of a key establishment scheme) and fixedinfo. SSKDF is also informally referred to as 'Concat KDF'.

Auxiliary function

The implementation uses a selectable auxiliary function H, which can be one of:

H(x) = hash(x, digest=md)
H(x) = HMAC_hash(x, key=salt, digest=md)
H(x) = KMACxxx(x, key=salt, custom="KDF", outlen=mac_size)

Both the HMAC and KMAC implementations set the key using the 'salt' value. The hash and HMAC also require the digest to be set.

Identity

``SSKDF'' is the name for this implementation; it can be used with the EVP_KDF_fetch() function.

Supported parameters

The supported parameters are:

"properties" (OSSL_KDF_PARAM_PROPERTIES) <UTF8 string>
"digest" (OSSL_KDF_PARAM_DIGEST) <UTF8 string>: This parameter is ignored for KMAC.
"mac" (OSSL_KDF_PARAM_MAC) <UTF8 string>
"maclen" (OSSL_KDF_PARAM_MAC_SIZE) <unsigned integer>
"salt" (OSSL_KDF_PARAM_SALT) <octet string>: These parameters work as described in ``PARAMETERS'' in EVP_KDF(3).
"key" (OSSL_KDF_PARAM_SECRET) <octet string>: This parameter set the shared secret that is used for key derivation.
"info" (OSSL_KDF_PARAM_INFO) <octet string>: This parameter sets an optional value for fixedinfo, also known as otherinfo.

NOTES

A context for SSKDF can be obtained by calling:

 EVP_KDF *kdf = EVP_KDF_fetch(NULL, "SSKDF", NULL);
 EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);

The output length of an SSKDF is specified via the keylen parameter to the EVP_KDF_derive(3) function.

EXAMPLES

This example derives 10 bytes using H(x) = SHA-256, with the secret key ``secret'' and fixedinfo value ``label'':

 EVP_KDF *kdf;
 EVP_KDF_CTX *kctx;
 unsigned char out[10];
 OSSL_PARAM params[4], *p = params;

 kdf = EVP_KDF_fetch(NULL, "SSKDF", NULL);
 kctx = EVP_KDF_CTX_new(kdf);
 EVP_KDF_free(kdf);

 *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
                                         SN_sha256, strlen(SN_sha256));
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
                                          "secret", (size_t)6);
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
                                          "label", (size_t)5);
 *p = OSSL_PARAM_construct_end();
 if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0) {
     error("EVP_KDF_derive");
 }

 EVP_KDF_CTX_free(kctx);

This example derives 10 bytes using H(x) = HMAC(SHA-256), with the secret key ``secret'', fixedinfo value ``label'' and salt ``salt'':

 EVP_KDF *kdf;
 EVP_KDF_CTX *kctx;
 unsigned char out[10];
 OSSL_PARAM params[6], *p = params;

 kdf = EVP_KDF_fetch(NULL, "SSKDF", NULL);
 kctx = EVP_KDF_CTX_new(kdf);
 EVP_KDF_free(kdf);

 *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC,
                                         SN_hmac, strlen(SN_hmac));
 *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
                                         SN_sha256, strlen(SN_sha256));
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SECRET,
                                          "secret", (size_t)6);
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
                                          "label", (size_t)5);
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
                                          "salt", (size_t)4);
 *p = OSSL_PARAM_construct_end();
 if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0) {
     error("EVP_KDF_derive");
 }

 EVP_KDF_CTX_free(kctx);

This example derives 10 bytes using H(x) = KMAC128(x,salt,outlen), with the secret key ``secret'' fixedinfo value ``label'', salt of ``salt'' and KMAC outlen of 20:

 EVP_KDF *kdf;
 EVP_KDF_CTX *kctx;
 unsigned char out[10];
 OSSL_PARAM params[6], *p = params;

 kdf = EVP_KDF_fetch(NULL, "SSKDF", NULL);
 kctx = EVP_KDF_CTX_new(kdf);
 EVP_KDF_free(kdf);

 *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC,
                                         SN_kmac128, strlen(SN_kmac128));
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SECRET,
                                          "secret", (size_t)6);
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
                                          "label", (size_t)5);
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
                                          "salt", (size_t)4);
 *p++ = OSSL_PARAM_construct_size_t(OSSL_KDF_PARAM_MAC_SIZE, (size_t)20);
 *p = OSSL_PARAM_construct_end();
 if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0) {
     error("EVP_KDF_derive");
 }

 EVP_KDF_CTX_free(kctx);

CONFORMING TO

NIST SP800-56Cr1.

HISTORY

This functionality was added in OpenSSL 3.0.

COPYRIGHT

Licensed under the Apache License 2.0 (the ``License''). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

Index

NAME

DESCRIPTION

Auxiliary function
Identity
Supported parameters

This document was created by man2html, using the manual pages.
Time: 11:43:41 GMT, May 07, 2024