| EVP_PKEY_CTX_set_hkdf_md(3) | OpenSSL | EVP_PKEY_CTX_set_hkdf_md(3) |
#include <openssl/kdf.h>
int EVP_PKEY_CTX_hkdf_mode(EVP_PKEY_CTX *pctx, int mode);
int EVP_PKEY_CTX_set_hkdf_md(EVP_PKEY_CTX *pctx, const EVP_MD *md);
int EVP_PKEY_CTX_set1_hkdf_salt(EVP_PKEY_CTX *pctx, unsigned char *salt,
int saltlen);
int EVP_PKEY_CTX_set1_hkdf_key(EVP_PKEY_CTX *pctx, unsigned char *key,
int keylen);
int EVP_PKEY_CTX_add1_hkdf_info(EVP_PKEY_CTX *pctx, unsigned char *info,
int infolen);
EVP_PKEY_CTX_hkdf_mode() sets the mode for the HKDF operation. There are three modes that are currently defined:
In this mode the digest, key, salt and info values must be set before a key is derived or an error occurs.
The digest, key and salt values must be set before a key is derived or an error occurs.
The digest, key and info values must be set before a key is derived or an error occurs.
EVP_PKEY_CTX_set_hkdf_md() sets the message digest associated with the HKDF.
EVP_PKEY_CTX_set1_hkdf_salt() sets the salt to saltlen bytes of the buffer salt. Any existing value is replaced.
EVP_PKEY_CTX_set1_hkdf_key() sets the key to keylen bytes of the buffer key. Any existing value is replaced.
EVP_PKEY_CTX_add1_hkdf_info() sets the info value to infolen bytes of the buffer info. If a value is already set, it is appended to the existing value.
A context for HKDF can be obtained by calling:
EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_HKDF, NULL);
The total length of the info buffer cannot exceed 1024 bytes in length: this should be more than enough for any normal use of HKDF.
The output length of an HKDF expand operation is specified via the length parameter to the EVP_PKEY_derive(3) function. Since the HKDF output length is variable, passing a NULL buffer as a means to obtain the requisite length is not meaningful with HKDF in any mode that performs an expand operation. Instead, the caller must allocate a buffer of the desired length, and pass that buffer to EVP_PKEY_derive(3) along with (a pointer initialized to) the desired length. Passing a NULL buffer to obtain the length is allowed when using EVP_PKEY_HKDEF_MODE_EXTRACT_ONLY.
Optimised versions of HKDF can be implemented in an ENGINE.
EVP_PKEY_CTX *pctx;
unsigned char out[10];
size_t outlen = sizeof(out);
pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_HKDF, NULL);
if (EVP_PKEY_derive_init(pctx) <= 0)
/* Error */
if (EVP_PKEY_CTX_set_hkdf_md(pctx, EVP_sha256()) <= 0)
/* Error */
if (EVP_PKEY_CTX_set1_hkdf_salt(pctx, "salt", 4) <= 0)
/* Error */
if (EVP_PKEY_CTX_set1_hkdf_key(pctx, "secret", 6) <= 0)
/* Error */
if (EVP_PKEY_CTX_add1_hkdf_info(pctx, "label", 5) <= 0)
/* Error */
if (EVP_PKEY_derive(pctx, out, &outlen) <= 0)
/* Error */
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>.
| 2018-12-08 | 1.1.1c |