66 lines
1.9 KiB
PHP
66 lines
1.9 KiB
PHP
<?php
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declare(strict_types=1);
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namespace TrilbyMedia\Cap;
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/**
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* Deterministic PRNG that must be bit-exact with the upstream cap.js
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* implementation in server/index.js. Used to regenerate the salt/target
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* pairs for each sub-challenge from the challenge token.
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*
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* JS uses 32-bit unsigned/int32 semantics. In PHP (64-bit) we emulate
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* that with explicit `& 0xFFFFFFFF` masks after every arithmetic op.
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*/
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final class Prng
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{
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private const UINT32_MASK = 0xFFFFFFFF;
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private const FNV_OFFSET = 0x811C9DC5; // 2166136261
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public static function generate(string $seed, int $length): string
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{
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if ($length <= 0) {
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return '';
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}
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$state = self::fnv1a($seed);
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$result = '';
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while (strlen($result) < $length) {
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$state = self::next($state);
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$result .= str_pad(dechex($state), 8, '0', STR_PAD_LEFT);
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}
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return substr($result, 0, $length);
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}
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private static function fnv1a(string $str): int
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{
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$hash = self::FNV_OFFSET;
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$len = strlen($str);
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for ($i = 0; $i < $len; $i++) {
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$hash = ($hash ^ ord($str[$i])) & self::UINT32_MASK;
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$s1 = ($hash << 1) & self::UINT32_MASK;
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$s4 = ($hash << 4) & self::UINT32_MASK;
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$s7 = ($hash << 7) & self::UINT32_MASK;
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$s8 = ($hash << 8) & self::UINT32_MASK;
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$s24 = ($hash << 24) & self::UINT32_MASK;
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$hash = ($hash + $s1 + $s4 + $s7 + $s8 + $s24) & self::UINT32_MASK;
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}
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return $hash;
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}
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private static function next(int $state): int
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{
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$state = ($state ^ (($state << 13) & self::UINT32_MASK)) & self::UINT32_MASK;
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$state = ($state ^ ($state >> 17)) & self::UINT32_MASK;
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$state = ($state ^ (($state << 5) & self::UINT32_MASK)) & self::UINT32_MASK;
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return $state;
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}
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}
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