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Diffstat (limited to 'www/wiki/includes/utils/MWCryptHKDF.php')
-rw-r--r-- | www/wiki/includes/utils/MWCryptHKDF.php | 103 |
1 files changed, 103 insertions, 0 deletions
diff --git a/www/wiki/includes/utils/MWCryptHKDF.php b/www/wiki/includes/utils/MWCryptHKDF.php new file mode 100644 index 00000000..1c8d4861 --- /dev/null +++ b/www/wiki/includes/utils/MWCryptHKDF.php @@ -0,0 +1,103 @@ +<?php +/** + * Extract-and-Expand Key Derivation Function (HKDF). A cryptographicly + * secure key expansion function based on RFC 5869. + * + * This relies on the secrecy of $wgSecretKey (by default), or $wgHKDFSecret. + * By default, sha256 is used as the underlying hashing algorithm, but any other + * algorithm can be used. Finding the secret key from the output would require + * an attacker to discover the input key (the PRK) to the hmac that generated + * the output, and discover the particular data, hmac'ed with an evolving key + * (salt), to produce the PRK. Even with md5, no publicly known attacks make + * this currently feasible. + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. + * http://www.gnu.org/copyleft/gpl.html + * + * @author Chris Steipp + * @file + */ + +use MediaWiki\MediaWikiServices; + +class MWCryptHKDF { + + /** + * Return a singleton instance, based on the global configs. + * @return CryptHKDF + */ + protected static function singleton() { + return MediaWikiServices::getInstance()->getCryptHKDF(); + } + + /** + * RFC5869 defines HKDF in 2 steps, extraction and expansion. + * From http://eprint.iacr.org/2010/264.pdf: + * + * The scheme HKDF is specifed as: + * HKDF(XTS, SKM, CTXinfo, L) = K(1) || K(2) || ... || K(t) + * where the values K(i) are defined as follows: + * PRK = HMAC(XTS, SKM) + * K(1) = HMAC(PRK, CTXinfo || 0); + * K(i+1) = HMAC(PRK, K(i) || CTXinfo || i), 1 <= i < t; + * where t = [L/k] and the value K(t) is truncated to its first d = L mod k bits; + * the counter i is non-wrapping and of a given fixed size, e.g., a single byte. + * Note that the length of the HMAC output is the same as its key length and therefore + * the scheme is well defined. + * + * XTS is the "extractor salt" + * SKM is the "secret keying material" + * + * N.B. http://eprint.iacr.org/2010/264.pdf seems to differ from RFC 5869 in that the test + * vectors from RFC 5869 only work if K(0) = '' and K(1) = HMAC(PRK, K(0) || CTXinfo || 1) + * + * @param string $hash The hashing function to use (e.g., sha256) + * @param string $ikm The input keying material + * @param string $salt The salt to add to the ikm, to get the prk + * @param string $info Optional context (change the output without affecting + * the randomness properties of the output) + * @param int $L Number of bytes to return + * @return string Cryptographically secure pseudorandom binary string + */ + public static function HKDF( $hash, $ikm, $salt, $info, $L ) { + return CryptHKDF::HKDF( $hash, $ikm, $salt, $info, $L ); + } + + /** + * Generate cryptographically random data and return it in raw binary form. + * + * @param int $bytes The number of bytes of random data to generate + * @param string $context String to mix into HMAC context + * @return string Binary string of length $bytes + */ + public static function generate( $bytes, $context ) { + return self::singleton()->generate( $bytes, $context ); + } + + /** + * Generate cryptographically random data and return it in hexadecimal string format. + * See MWCryptRand::realGenerateHex for details of the char-to-byte conversion logic. + * + * @param int $chars The number of hex chars of random data to generate + * @param string $context String to mix into HMAC context + * @return string Random hex characters, $chars long + */ + public static function generateHex( $chars, $context = '' ) { + $bytes = ceil( $chars / 2 ); + $hex = bin2hex( self::singleton()->generate( $bytes, $context ) ); + return substr( $hex, 0, $chars ); + } + +} |