EVP_KDF-HKDF - The HKDF EVP_KDF implementation
Support for computing the HKDF KDF through the EVP_KDF API.
The EVP_KDF-HKDF algorithm implements the HKDF key derivation function. HKDF follows the "extract-then-expand" paradigm, where the KDF logically consists of two modules. The first stage takes the input keying material and "extracts" from it a fixed-length pseudorandom key K. The second stage "expands" the key K into several additional pseudorandom keys (the output of the KDF).
"HKDF" is the name for this implementation; it can be used with the EVP_KDF_fetch() function.
The supported parameters are:
These parameters work as described in "info" (OSSL_KDF_PARAM_INFO) <octet string>
This parameter sets the info value. The length of the context info buffer cannot exceed 1024 bytes; this should be more than enough for any normal use of HKDF. This parameter sets the mode for the HKDF operation. There are three modes that are currently defined: This is the default mode. Calling EVP_KDF_HKDF_MODE_EXTRACT_ONLY "EXTRACT_ONLY"
In this mode calling EVP_KDF_HKDF_MODE_EXPAND_ONLY "EXPAND_ONLY"
In this mode calling NOTES
A context for HKDF can be obtained by calling: The output length of an HKDF expand operation is specified via the keylen parameter to the EXAMPLES
This example derives 10 bytes using SHA-256 with the secret key "secret", salt value "salt" and info value "label": RFC 5869 EVP_KDF_CTX_new(3), EVP_KDF_size(3), EVP_KDF_derive(3), COPYRIGHT
Copyright 2016-2019 The OpenSSL Project Authors. 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.
EVP_KDF *kdf = EVP_KDF_fetch(NULL, "HKDF", NULL);
EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf); EVP_KDF *kdf;
EVP_KDF_CTX *kctx;
unsigned char out[10];
OSSL_PARAM params[5], *p = params;
kdf = EVP_KDF_fetch(NULL, "HKDF", 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_octet_string(OSSL_KDF_PARAM_SALT,
"salt", (size_t)4);
*p = OSSL_PARAM_construct_end();
if (EVP_KDF_CTX_set_params(kctx, params) <= 0) {
error("EVP_KDF_CTX_set_params");
}
if (EVP_KDF_derive(kctx, out, sizeof(out)) <= 0) {
error("EVP_KDF_derive");
}
EVP_KDF_CTX_free(kctx);CONFORMING TO
SEE ALSO