How Can I Generate Secure Random Numbers in PHP for Sensitive Applications?

Secure Random Number Generation in PHP

Generating secure random numbers in PHP is crucial for applications like password resets, where the original password is hashed and unavailable. While mt_rand is insufficient, the operating system or cryptographic random number modules may not be accessible.

Proposed Solution and Concerns

A proposed approach involves storing an initial seed and calculating subsequent random numbers using a formula:

result = seed
seed = sha512(seed . mt_rand())

While sha512 is secure, using it here is faulty. The mt_rand call does not enhance security, and the seed is canceled out. This misconception suggests weaknesses in the design of security systems.

Recommended Approach

Instead of relying on hashes to generate entropy, it's highly recommended to use the system's entropy sources:

• Unix/Linux: /dev/urandom
• Windows: crypto-api

Here's sample PHP code from php.net to obtain a secure 128-bit string from these sources:

$pr_bits = '';

// Unix/Linux platform
$fp = @fopen('/dev/urandom','rb');
if ($fp !== FALSE) {
    $pr_bits .= @fread($fp,16);
    @fclose($fp);
}

// MS-Windows platform
if (@class_exists('COM')) {
    try {
        $CAPI_Util = new COM('CAPICOM.Utilities.1');
        $pr_bits .= $CAPI_Util->GetRandom(16,0);
    } catch (Exception $ex) {
        // Handle exception
    }
}

if (strlen($pr_bits) < 16) {
    // Handle entropy source issue
}

Using this approach ensures secure random number generation, which is essential for protecting sensitive data in PHP applications.

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