=head1 NAME
EVP_PKEY_CTX_set_hkdf_md, EVP_PKEY_CTX_set1_hkdf_salt,
-EVP_PKEY_CTX_set1_hkdf_key, EVP_PKEY_CTX_add1_hkdf_info -
+EVP_PKEY_CTX_set1_hkdf_key, EVP_PKEY_CTX_add1_hkdf_info,
+EVP_PKEY_CTX_hkdf_mode -
HMAC-based Extract-and-Expand key derivation algorithm
=head1 SYNOPSIS
#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,
"expands" the key K into several additional pseudorandom keys (the output
of the KDF).
+EVP_PKEY_CTX_hkdf_mode() sets the mode for the HKDF operation. There are three
+modes that are currently defined:
+
+=over 4
+
+=item EVP_PKEY_HKDEF_MODE_EXTRACT_AND_EXPAND
+
+This is the default mode. Calling L<EVP_PKEY_derive(3)> on an EVP_PKEY_CTX set
+up for HKDF will perform an extract followed by an expand operation in one go.
+The derived key returned will be the result after the expand operation. The
+intermediate fixed-length pseudorandom key K is not returned.
+
+In this mode the digest, key, salt and info values must be set before a key is
+derived or an error occurs.
+
+=item EVP_PKEY_HKDEF_MODE_EXTRACT_ONLY
+
+In this mode calling L<EVP_PKEY_derive(3)> will just perform the extract
+operation. The value returned will be the intermediate fixed-length pseudorandom
+key K.
+
+The digest, key and salt values must be set before a key is derived or an
+error occurs.
+
+=item EVP_PKEY_HKDEF_MODE_EXPAND_ONLY
+
+In this mode calling L<EVP_PKEY_derive(3)> will just perform the expand
+operation. The input key should be set to the intermediate fixed-length
+pseudorandom key K returned from a previous extract operation.
+
+The digest, key and info values must be set before a key is derived or an
+error occurs.
+
+=back
+
EVP_PKEY_set_hkdf_md() sets the message digest associated with the HKDF.
EVP_PKEY_CTX_set1_hkdf_salt() sets the salt to B<saltlen> bytes of the
L<EVP_PKEY_CTX_ctrl_str(3)>.
The B<type> parameter "md" uses the supplied B<value> as the name of the digest
algorithm to use.
+The B<type> parameter "mode" uses the values "EXTRACT_AND_EXPAND",
+"EXTRACT_ONLY" and "EXPAND_ONLY" to determine the mode to use.
The B<type> parameters "salt", "key" and "info" use the supplied B<value>
parameter as a B<seed>, B<key> or B<info> value.
The names "hexsalt", "hexkey" and "hexinfo" are similar except they take a hex
EVP_PKEY_CTX *pctx = EVP_PKEY_new_id(EVP_PKEY_HKDF, NULL);
-The digest, key, salt and info values must be set before a key is derived or
-an error occurs.
-
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 the KDF is specified via the length parameter to the
-L<EVP_PKEY_derive(3)> function.
+The output length of an HKDF expand operation is specified via the length
+parameter to the L<EVP_PKEY_derive(3)> function.
Since the HKDF output length is variable, passing a B<NULL> buffer as a means
-to obtain the requisite length is not meaningful with HKDF.
-Instead, the caller must allocate a buffer of the desired length, and pass that
-buffer to L<EVP_PKEY_derive(3)> along with (a pointer initialized to) the
-desired length.
+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 L<EVP_PKEY_derive(3)> along with (a
+pointer initialized to) the desired length. Passing a B<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.
pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_HKDF, NULL);
if (EVP_PKEY_derive_init(pctx) <= 0)
- /* Error */
+ /* Error */
if (EVP_PKEY_CTX_set_hkdf_md(pctx, EVP_sha256()) <= 0)
- /* Error */
- if (EVP_PKEY_CTX_set1_salt(pctx, "salt", 4) <= 0)
- /* Error */
- if (EVP_PKEY_CTX_set1_key(pctx, "secret", 6) <= 0)
- /* Error */
- if (EVP_PKEY_CTX_add1_hkdf_info(pctx, "label", 6) <= 0)
- /* Error */
+ /* 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 */
+ /* Error */
=head1 CONFORMING TO
projects / openssl.git / blobdiff