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

Migrating from Mcrypt to OpenSSL in PHP 7.2

The upcoming PHP 7.2 release will mark the deprecation of the Mcrypt extension, prompting developers to embrace the more secure OpenSSL alternative. This article examines the transition, particularly focusing on the challenges involved in preserving AES 256 CBC encryption and IVs.

Compatibility Concerns

The primary obstacle in the migration is the incompatible encryption algorithms. Mcrypt employs the Rijndael-256 algorithm, while OpenSSL supports AES-256, which is a variant of Rijndael-128 with a 256-bit key. Hence, the encryption cannot be directly converted without re-encrypting all data.

Security Considerations

The Mcrypt code provided in the question exhibits several vulnerabilities, including:

• Lack of authentication
• Inadequate padding
• Susceptibility to byte-oriented attacks

OpenSSL automatically applies PKCS#5 padding, but it is strongly recommended to adopt a robust encryption library like defuse/php-encryption, which offers additional protection and simplifies the process.

Implementation

To migrate to OpenSSL, consider the following steps:

1. Re-encrypt all data using AES-256 with the appropriate padding and authentication mechanisms.
2. Update your code to utilize the OpenSSL extension for encryption and decryption.
3. Employ a reputable encryption library to enhance security.

By addressing these compatibility and security aspects, developers can seamlessly transition from Mcrypt to OpenSSL, ensuring the integrity and confidentiality of their sensitive data in PHP 7.2 and beyond.

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