diff options
Diffstat (limited to 'deps/openssl/openssl/doc/man3/EVP_PKEY_CTX_set_hkdf_md.pod')
| -rw-r--r-- | deps/openssl/openssl/doc/man3/EVP_PKEY_CTX_set_hkdf_md.pod | 166 |
1 files changed, 166 insertions, 0 deletions
diff --git a/deps/openssl/openssl/doc/man3/EVP_PKEY_CTX_set_hkdf_md.pod b/deps/openssl/openssl/doc/man3/EVP_PKEY_CTX_set_hkdf_md.pod new file mode 100644 index 0000000000..e8f19cfc99 --- /dev/null +++ b/deps/openssl/openssl/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 |