EVP_KDF-KRB5KDF - The RFC3961 Krb5 KDF EVP_KDF implementation
Support for computing the KRB5KDF KDF through the EVP_KDF API.
The EVP_KDF-KRB5KDF algorithm implements the key derivation function defined in RFC 3961, section 5.1 and is used by Krb5 to derive session keys. Three inputs are required to perform key derivation: a cipher, (for example AES-128-CBC), the initial key, and a constant.
"KRB5KDF" 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 "constant" (OSSL_KDF_PARAM_CONSTANT) <octet string>
This parameter sets the constant value for the KDF. If a value is already set, the contents are replaced.
A context for KRB5KDF can be obtained by calling:
EVP_KDF *kdf = EVP_KDF_fetch(NULL, "KRB5KDF", NULL);
EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);The output length of the KRB5KDF derivation is specified via the keylen parameter to the EVP_KDF_size(3) to obtain the requisite length returns the correct length only after the cipher is set. Prior to that EVP_MAX_KEY_LENGTH is returned. The caller must allocate a buffer of the correct length for the chosen cipher, and pass that buffer to the EXAMPLES
This example derives a key using the AES-128-CBC cipher: RFC 3961 EVP_KDF_CTX_free(3), EVP_KDF_size(3), "PARAMETERS" in EVP_KDF(3) This functionality was added to OpenSSL 3.0. Copyright 2016-2019 The OpenSSL Project Authors. All Rights Reserved. Licensed under the OpenSSL license (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_CTX *kctx;
unsigned char key[16] = "01234...";
unsigned char constant[] = "I'm a constant";
unsigned char out[16];
size_t outlen = sizeof(out);
OSSL_PARAM params[4], *p = params;
kdf = EVP_KDF_fetch(NULL, "KRB5KDF", NULL);
kctx = EVP_KDF_CTX_new(kdf);
EVP_KDF_free(kdf);
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_CIPHER,
SN_aes_128_cbc,
strlen(SN_aes_128_cbc));
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
key, (size_t)16);
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_CONSTANT,
constant, strlen(constant));
*p = OSSL_PARAM_construct_end();
if (EVP_KDF_set_params(kctx, params) <= 0)
/* Error */
if (EVP_KDF_derive(kctx, out, outlen) <= 0)
/* Error */
EVP_KDF_CTX_free(kctx);CONFORMING TO
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