Updated: 2022/Sep/29

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EVP_KDF-SS(7)                       OpenSSL                      EVP_KDF-SS(7)



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" (EVP_KDF_CTRL_SET_KEY) <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(EVP_KDF_CTRL_SET_KEY,
                                                 "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(EVP_KDF_CTRL_SET_KEY,
                                                 "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.

SEE ALSO
       EVP_KDF(3), EVP_KDF_CTX_new(3), EVP_KDF_CTX_free(3),
       EVP_KDF_CTX_set_params(3), EVP_KDF_CTX_get_kdf_size(3),
       EVP_KDF_derive(3), "PARAMETERS" in EVP_KDF(3)

HISTORY
       This functionality was added in OpenSSL 3.0.

COPYRIGHT
       Copyright 2019-2023 The OpenSSL Project Authors. All Rights Reserved.
       Copyright (c) 2019, Oracle and/or its affiliates.  All rights reserved.

       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>.



3.0.12                            2023-05-07                     EVP_KDF-SS(7)