How Can I Safely Migrate My PHP Encryption from Mcrypt to OpenSSL?

Avoiding Encryption Headaches: Transitioning from Mcrypt to OpenSSL

Mcrypt, a legacy PHP module, will cease support in PHP 7.2. Its recommended replacement, OpenSSL, has slightly different implementation nuances. This article explores how to effectively migrate code from Mcrypt to OpenSSL while maintaining critical encryption properties.

Converting Mcrypt Code to OpenSSL

Specifically, let's consider the following Mcrypt code that utilizes AES 256 CBC encryption:

function encrypt($masterPassword, $data) {
    // ... (Omitted for brevity)
    return base64_encode($iv . $encrypted);
}

function decrypt($masterPassword, $base64) {
    // ... (Omitted for brevity)
    return trim($decrypted);
}

It's crucial to note that Rijndael-256 (used by Mcrypt) is not identical to AES-256 (used by OpenSSL). OpenSSL lacks Rijndael-256 support.

Re-encryption Required

Consequently, direct conversion is not feasible. Instead, all encrypted data must be re-encrypted using AES-256 under OpenSSL.

Addressing Additional Issues

Furthermore, the original code exhibits several significant encryption concerns:

• Absence of authentication (easily added using HMACs)
• Improper padding (PKCS#5 padding is recommended)
• Non-byte-safe operations (e.g., mb_substr())

OpenSSL simplifies padding, but a dedicated encryption library like defuse/php-encryption can enhance security and convenience even further.

Conclusion

Transitioning from Mcrypt to OpenSSL requires careful consideration of these encryption subtleties. By re-encrypting data and addressing additional vulnerabilities, developers can continue to secure their applications effectively in the absence of Mcrypt support. OpenSSL and defuse/php-encryption offer robust alternatives for reliable encryption.

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