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.

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>.