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.

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>.