EVP_KDF_SS - The Single Step / One Step EVP_KDF implementation
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'.
The implementation uses a selectable auxiliary function H, which can be in the backported version only a:
EVP_KDF_SS is the numeric identity for this implementation; it can be used with the EVP_KDF_CTX_new_id() function.
The supported controls are:
This control works as described in "CONTROLS" in EVP_KDF_CTX(3).
This control expects two arguments: unsigned char *secret, size_t secretlen
The shared secret used for key derivation. This control sets the secret.
EVP_KDF_ctrl_str() takes two type strings for this control:
The value string is used as is.
The value string is expected to be a hexadecimal number, which will be decoded before being passed on as the control value.
This control expects two arguments: unsigned char *info, size_t infolen
An optional value for fixedinfo, also known as otherinfo. This control sets the fixedinfo.
EVP_KDF_ctrl_str() takes two type strings for this control:
The value string is used as is.
The value string is expected to be a hexadecimal number, which will be decoded before being passed on as the control value.
A context for SSKDF can be obtained by calling:
EVP_KDF_CTX *kctx = EVP_KDF_CTX_new_id(EVP_KDF_SS);
The output length of an SSKDF is specified via the keylen parameter to the EVP_KDF_derive(3) function.
This example derives 10 bytes using H(x) = SHA-256, with the secret key "secret" and fixedinfo value "label":
EVP_KDF_CTX *kctx;
unsigned char out[10];
kctx = EVP_KDF_CTX_new_id(EVP_KDF_SS);
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_MD, EVP_sha256()) <= 0) {
error("EVP_KDF_CTRL_SET_MD");
}
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_KEY, "secret", (size_t)6) <= 0) {
error("EVP_KDF_CTRL_SET_KEY");
}
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_SSKDF_INFO, "label", (size_t)5) <= 0) {
error("EVP_KDF_CTRL_SET_SSKDF_INFO");
}
if (EVP_KDF_derive(kctx, out, sizeof(out)) <= 0) {
error("EVP_KDF_derive");
}
EVP_KDF_CTX_free(kctx);NIST SP800-56Cr1.
EVP_KDF_CTX, EVP_KDF_CTX_new_id(3), EVP_KDF_CTX_free(3), EVP_KDF_ctrl(3), EVP_KDF_size(3), EVP_KDF_derive(3), "CONTROLS" in EVP_KDF_CTX(3)
This functionality was added to OpenSSL 3.0.0.
Copyright 2019 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.