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