How Can I Securely Migrate from MCrypt to OpenSSL in PHP 7.2 and Beyond?

Preparing for the Deprecation of Mcrypt in PHP 7.2

With PHP 7.2 on the horizon, the mcrypt extension is slated for removal. While openssl offers an alternative, the transition from mcrypt to openssl can pose challenges, especially when aiming to maintain AES 256 CBC encryption and preserve IVs.

Bridging the Gap from Mcrypt to Openssl

The core issue lies in the fact that Rijndael-256, employed by mcrypt, differs from AES-256 handled by openssl. As openssl doesn't support Rijndael-256, a direct conversion is not possible.

To address this, all data encrypted using Rijndael-256 must be re-encrypted using openssl's AES-256. This process requires careful planning to avoid data loss or corruption.

Addressing Potential Vulnerabilities

Beyond the technical differences, the provided mcrypt code also demonstrates several vulnerabilities that must be mitigated in the new implementation:

• Lack of Authentication: The current scheme does not incorporate authentication mechanisms (e.g., HMACs) to secure the data against tampering.
• Padding Deficiencies: Mcrypt employs zero-padding, which is insufficient for ensuring security in block mode encryption. PKCS#5 or similar padding methods should be adopted.
• Byte Safety: Using mb_substr(), as seen in the code, can lead to byte handling issues. Proper byte handling practices should be incorporated.

Embracing Secure Encryption Practices

While openssl provides automated PKCS#5 padding, it is recommended to utilize a robust encryption library, such as defuse/php-encryption. This library addresses the identified vulnerabilities and offers a comprehensive encryption solution. By implementing these best practices, you can effectively transition to openssl and maintain the security of your data.

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