Imported OpenSSL 1.1.1a

doc/man3/EVP_PKEY_CTX_set_hkdf_md.pod

@@ -0,0 +1,166 @@
+=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_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,
+                                 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_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
+
+All these functions are implemented as macros.
+
+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 EXAMPLE
+
+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 COPYRIGHT
+
+Copyright 2016-2018 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
+L<https://www.openssl.org/source/license.html>.
+
+=cut