NAME<\/a> EVP_KDF_HKDF \u2212 The HKDF EVP_KDF implementation<\/p>\n Support for computing the HKDF<\/small><\/b> KDF<\/small> through the EVP_KDF<\/small><\/b> API.<\/small><\/p>\n The EVP_KDF_HKDF<\/small> algorithm implements the HKDF<\/small> key derivation function. HKDF<\/small> follows the “extract-then-expand” paradigm, where the KDF<\/small> 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<\/small> ).<\/p>\n Numeric identity Supported controls<\/b> These controls work as described in ” CONTROLS”<\/small> in EVP_KDF_CTX<\/small><\/b> (3).<\/p>\n EVP_KDF_CTRL_RESET_HKDF_INFO<\/small><\/b><\/p>\n This control does not expect any arguments.<\/p>\n Resets the context info buffer to zero length.<\/p>\n EVP_KDF_CTRL_ADD_HKDF_INFO<\/small><\/b><\/p>\n This control expects two arguments: “unsigned char *info”, “size_t infolen”<\/p>\n Sets the info value to the first infolen<\/b> bytes of the buffer info<\/b>. If a value is already set, the contents of the buffer are appended to the existing value.<\/p>\n The total length of the context info buffer cannot exceed 1024 bytes; this should be more than enough for any normal use of HKDF.<\/small><\/p>\n EVP_KDF_ctrl_str()<\/b> takes two type strings for this control: The value string is used as is.<\/p>\n “hexinfo”<\/p>\n The value string is expected to be a hexadecimal number, which will be decoded before being passed on as the control value.<\/p>\n EVP_KDF_CTRL_SET_HKDF_MODE<\/small><\/b><\/p>\n This control expects one argument: “int mode”<\/p>\n Sets the mode for the HKDF<\/small> operation. There are three modes that are currently defined: This is the default mode. Calling EVP_KDF_derive<\/b>(3) on an EVP_KDF_CTX<\/small> set up for HKDF<\/small> 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.<\/p>\n In this mode the digest, key, salt and info values must be set before a key is derived otherwise an error will occur.<\/p>\n EVP_KDF_HKDF_MODE_EXTRACT_ONLY<\/small><\/p>\n In this mode calling EVP_KDF_derive<\/b>(3) will just perform the extract operation. The value returned will be the intermediate fixed-length pseudorandom key K. The “keylen” parameter must match the size of K, which can be looked up by calling EVP_KDF_size()<\/b> after setting the mode and digest.<\/p>\n The digest, key and salt values must be set before a key is derived otherwise an error will occur.<\/p>\n EVP_KDF_HKDF_MODE_EXPAND_ONLY<\/small><\/p>\n In this mode calling EVP_KDF_derive<\/b>(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.<\/p>\n The digest, key and info values must be set before a key is derived otherwise an error will occur.<\/p>\n EVP_KDF_ctrl_str()<\/b> type string: “mode”<\/p>\n The value string is expected to be one of: ” EXTRACT_AND_EXPAND”, “EXTRACT_ONLY”<\/small> or ” EXPAND_ONLY”.<\/small><\/p>\n A context for HKDF<\/small> can be obtained by calling:<\/p>\n EVP_KDF_CTX *kctx = EVP_KDF_CTX_new_id(EVP_KDF_HKDF);<\/p>\n The output length of an HKDF<\/small> expand operation is specified via the “keylen” parameter to the EVP_KDF_derive<\/b>(3) function. When using EVP_KDF_HKDF_MODE_EXTRACT_ONLY<\/small> the “keylen” parameter must equal the size of the intermediate fixed-length pseudorandom key otherwise an error will occur. For that mode, the fixed output size can be looked up by calling EVP_KDF_size()<\/b> after setting the mode and digest on the “EVP_KDF_CTX”.<\/p>\n This example derives 10 bytes using SHA\u2212256<\/small> with the secret key “secret”, salt value “salt” and info value “label”:<\/p>\n EVP_KDF_CTX *kctx; RFC 5869<\/small><\/p>\n EVP_KDF_CTX<\/small> , EVP_KDF_CTX_new_id<\/b>(3), EVP_KDF_CTX_free<\/b>(3), EVP_KDF_ctrl<\/b>(3), EVP_KDF_size<\/b>(3), EVP_KDF_derive<\/b>(3), ” CONTROLS”<\/small> in EVP_KDF_CTX<\/small><\/b> (3)<\/p>\n Copyright 2016\u22122018 The OpenSSL Project Authors. All Rights Reserved.<\/p>\n 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<\/small> in the source distribution or at EVP_KDF_HKDF \u2212 The HKDF EVP_KDF implementation <\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[971],"tags":[973,1096,972],"class_list":["post-4008","post","type-post","status-publish","format-standard","hentry","category-7-miscelanea","tag-973","tag-evp_kdf_hkdf","tag-man7"],"gutentor_comment":0,"_links":{"self":[{"href":"https:\/\/lode.uno\/linux-man\/wp-json\/wp\/v2\/posts\/4008","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/lode.uno\/linux-man\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/lode.uno\/linux-man\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/lode.uno\/linux-man\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/lode.uno\/linux-man\/wp-json\/wp\/v2\/comments?post=4008"}],"version-history":[{"count":0,"href":"https:\/\/lode.uno\/linux-man\/wp-json\/wp\/v2\/posts\/4008\/revisions"}],"wp:attachment":[{"href":"https:\/\/lode.uno\/linux-man\/wp-json\/wp\/v2\/media?parent=4008"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/lode.uno\/linux-man\/wp-json\/wp\/v2\/categories?post=4008"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/lode.uno\/linux-man\/wp-json\/wp\/v2\/tags?post=4008"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
DESCRIPTION<\/a>
NOTES<\/a>
EXAMPLE<\/a>
CONFORMING TO<\/a>
SEE ALSO<\/a>
COPYRIGHT<\/a> <\/p>\n
\nNAME <\/a> <\/h2>\n
DESCRIPTION <\/a> <\/h2>\n
EVP_KDF_HKDF<\/small><\/b> is the numeric identity for this implementation; it can be used with the EVP_KDF_CTX_new_id()<\/b> function.<\/p>\n
The supported controls are:
EVP_KDF_CTRL_SET_SALT
EVP_KDF_CTRL_SET_MD
EVP_KDF_CTRL_SET_KEY<\/small><\/b><\/p>\n
“info”<\/p>\n
EVP_KDF_HKDF_MODE_EXTRACT_AND_EXPAND<\/small><\/p>\nNOTES <\/a> <\/h2>\n
EXAMPLE <\/a> <\/h2>\n
unsigned char out[10];
kctx = EVP_KDF_CTX_new_id(EVP_KDF_HKDF);
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_MD, EVP_sha256()) <= 0) {
error(“EVP_KDF_CTRL_SET_MD”);
}
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_SALT, “salt”, (size_t)4) <= 0) {
error(“EVP_KDF_CTRL_SET_SALT”);
}
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_KEY, “secret”, (size_t)6) <= 0) {
error(“EVP_KDF_CTRL_SET_KEY”);
}
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_ADD_HKDF_INFO, “label”, (size_t)5) <= 0) {
error(“EVP_KDF_CTRL_ADD_HKDF_INFO”);
}
if (EVP_KDF_derive(kctx, out, sizeof(out)) <= 0) {
error(“EVP_KDF_derive”);
}
EVP_KDF_CTX_free(kctx);<\/p>\nCONFORMING TO <\/a> <\/h2>\n
SEE ALSO <\/a> <\/h2>\n
COPYRIGHT <\/a> <\/h2>\n
\n","protected":false},"excerpt":{"rendered":"