bcrypt_cost_benchmark.php

<?php

/**
 * `password_hash`/bcrypt cost benchmark script
 *
 * Usage:
 *     $ php bcrypt_cost_benchmark.php <lower cost> <higher cost> <n_tries>
 *
 * Example: Run 100 tries of costs 8 through 12
 *     $ php bcrypt_cost_benchmark.php 8 12 100
 */

if ($argc < 4) {
    echo "Usage: {$argv[0]} <lower cost> <higher cost> <n_tries>\n";
    exit(1);
}

$cost_lower = intval($argv[1]);
$cost_upper = intval($argv[2]);
$string = 'DjpK|WsAqqk",/@ANXIDDbiU%R';

$tries = intval($argv[3]);


// Run the benchmark
$rawdata = [];
for ($cost = $cost_lower; $cost <= $cost_upper; $cost += 1) {
    $rawdata[$cost] = [];

    $cost_progress = sprintf("Benchmarking cost: %2d", $cost);
    printf($cost_progress); flush();

    for ($n = 0; $n < $tries; $n += 1) {
        $time_start = microtime(true);
        password_hash($string, PASSWORD_BCRYPT, ['cost' => $cost]);
        $time_end = microtime(true);

        $delta = $time_end - $time_start;
        $rawdata[$cost][] = $delta;
    }

    echo(str_repeat("\x08", strlen($cost_progress))); flush();
}


// Calculate mean and std-dev
$results = [];
for ($cost = $cost_lower; $cost <= $cost_upper; $cost += 1) {
    $results[$cost] = [];

    $sum = array_sum($rawdata[$cost]);

    $mean = $sum / $tries;
    $results[$cost]['mean'] = $mean;

    // Variance
    $sq_diff = array_map(
        function ($n) use ($mean) { return ($n - $mean) ** 2; },
        $rawdata[$cost]
    );

    $variance = array_sum($sq_diff) / $tries;
    $stddev = sqrt($variance);
    $results[$cost]['stddev'] = $stddev;
}


// Print the results
$fmt = "%2d: %6.4F ± %6.4F s (%4.1F hashes/s)\n"; // for sprintf
for ($cost = $cost_lower; $cost <= $cost_upper; $cost += 1) {
    $result = $results[$cost];
    printf(
        $fmt, $cost,
        round($result['mean'], 4),
        round($result['stddev'], 4),
        round(1/$result['mean'], 1)
    );
}

exit(0);