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ConcatKDF.php
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ConcatKDF.php
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<?php
declare(strict_types=1);
/*
* The MIT License (MIT)
*
* Copyright (c) 2014-2018 Spomky-Labs
*
* This software may be modified and distributed under the terms
* of the MIT license. See the LICENSE file for details.
*/
namespace Jose\Component\Encryption\Util;
use Base64Url\Base64Url;
/**
* @internal
*
* @see https://tools.ietf.org/html/rfc7518#section-4.6.2
*/
class ConcatKDF
{
/**
* Key Derivation Function.
*
* @param string $Z Shared secret
* @param string $algorithm Encryption algorithm
* @param int $encryption_key_size Size of the encryption key
* @param string $apu Agreement PartyUInfo (information about the producer)
* @param string $apv Agreement PartyVInfo (information about the recipient)
*/
public static function generate(string $Z, string $algorithm, int $encryption_key_size, string $apu = '', string $apv = ''): string
{
$apu = !empty($apu) ? Base64Url::decode($apu) : '';
$apv = !empty($apv) ? Base64Url::decode($apv) : '';
$encryption_segments = [
self::toInt32Bits(1), // Round number 1
$Z, // Z (shared secret)
self::toInt32Bits(\mb_strlen($algorithm, '8bit')).$algorithm, // Size of algorithm's name and algorithm
self::toInt32Bits(\mb_strlen($apu, '8bit')).$apu, // PartyUInfo
self::toInt32Bits(\mb_strlen($apv, '8bit')).$apv, // PartyVInfo
self::toInt32Bits($encryption_key_size), // SuppPubInfo (the encryption key size)
'', // SuppPrivInfo
];
$input = \implode('', $encryption_segments);
$hash = \hash('sha256', $input, true);
$kdf = \mb_substr($hash, 0, $encryption_key_size / 8, '8bit');
return $kdf;
}
/**
* Convert an integer into a 32 bits string.
*
* @param int $value Integer to convert
*/
private static function toInt32Bits(int $value): string
{
return \hex2bin(\str_pad(\dechex($value), 8, '0', STR_PAD_LEFT));
}
}