doc/man3/EVP_PKEY_CTX_set_hkdf_md.pod - third_party/openssl - Git at Google

 =pod

 =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_set_hkdf_mode -
 HMAC-based Extract-and-Expand key derivation algorithm

 =head1 SYNOPSIS

  #include <openssl/kdf.h>

  int EVP_PKEY_CTX_set_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);

 =head1 DESCRIPTION

 The EVP_PKEY_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).

 EVP_PKEY_CTX_set_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_CTX_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
 buffer B<salt>. Any existing value is replaced.

 EVP_PKEY_CTX_set1_hkdf_key() sets the key to B<keylen> bytes of the buffer
 B<key>. Any existing value is replaced.

 EVP_PKEY_CTX_add1_hkdf_info() sets the info value to B<infolen> bytes of the
 buffer B<info>. If a value is already set, it is appended to the existing
 value.

 =head1 STRING CTRLS

 HKDF also supports string based control operations via
 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
 string which is converted to binary.

 =head1 NOTES

 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 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 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.

 =head1 RETURN VALUES

 All these functions return 1 for success and 0 or a negative value for failure.
 In particular a return value of -2 indicates the operation is not supported by
 the public key algorithm.

 =head1 EXAMPLES

 This example derives 10 bytes using SHA-256 with the secret key "secret",
 salt value "salt" and info value "label":

  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 */

 =head1 CONFORMING TO

 RFC 5869

 =head1 SEE ALSO

 L<EVP_PKEY_CTX_new(3)>,
 L<EVP_PKEY_CTX_ctrl_str(3)>,
 L<EVP_PKEY_derive(3)>

 =head1 HISTORY

 All of the functions described here were converted from macros to functions in
 OpenSSL 3.0.

 =head1 COPYRIGHT

 Copyright 2016-2021 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
 L<https://www.openssl.org/source/license.html>.

 =cut
	=pod

	=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_set_hkdf_mode -
	HMAC-based Extract-and-Expand key derivation algorithm

	=head1 SYNOPSIS

	#include <openssl/kdf.h>

	int EVP_PKEY_CTX_set_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);

	=head1 DESCRIPTION

	The EVP_PKEY_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).

	EVP_PKEY_CTX_set_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_CTX_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
	buffer B<salt>. Any existing value is replaced.

	EVP_PKEY_CTX_set1_hkdf_key() sets the key to B<keylen> bytes of the buffer
	B<key>. Any existing value is replaced.

	EVP_PKEY_CTX_add1_hkdf_info() sets the info value to B<infolen> bytes of the
	buffer B<info>. If a value is already set, it is appended to the existing
	value.

	=head1 STRING CTRLS

	HKDF also supports string based control operations via
	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
	string which is converted to binary.

	=head1 NOTES

	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 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 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.

	=head1 RETURN VALUES

	All these functions return 1 for success and 0 or a negative value for failure.
	In particular a return value of -2 indicates the operation is not supported by
	the public key algorithm.

	=head1 EXAMPLES

	This example derives 10 bytes using SHA-256 with the secret key "secret",
	salt value "salt" and info value "label":

	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 */

	=head1 CONFORMING TO

	RFC 5869

	=head1 SEE ALSO

	L<EVP_PKEY_CTX_new(3)>,
	L<EVP_PKEY_CTX_ctrl_str(3)>,
	L<EVP_PKEY_derive(3)>

	=head1 HISTORY

	All of the functions described here were converted from macros to functions in
	OpenSSL 3.0.

	=head1 COPYRIGHT

	Copyright 2016-2021 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
	L<https://www.openssl.org/source/license.html>.

	=cut