How to Migrate from Mcrypt to OpenSSL for Blowfish Encryption?

Migrating from Mcrypt to OpenSSL

Your current implementation utilizes Mcrypt for encryption, but you aim to transition to OpenSSL. Mcrypt's blowfish cipher in ECB mode exhibits differences from OpenSSL, such as requiring an IV length of 56 for Mcrypt and 0 for OpenSSL.

To seamlessly migrate the modules:

• Understand the Padding Difference:

  • Mcrypt uses PKCS#5 padding, while OpenSSL uses PKCS#7. Ensure consistent padding when encrypting data.

• Manual Padding:

  • Since OpenSSL uses PKCS#7, you must manually pad data before encrypting it with Mcrypt. This involves appending "1" to the data.

• IV Initialization:

  • ECB mode does not utilize IV. Therefore, when using ECB with OpenSSL, your code should remove IV initialization.

• Key Length Considerations:

  • Mcrypt supports key sizes up to 56 bytes, whereas OpenSSL does not have a key size limit. Adjust your key size accordingly.

• Re-Encryption:

  • To ensure compatibility, consider re-encrypting your existing Mcrypt-encrypted data using OpenSSL. This eliminates any discrepancies due to the different padding algorithms.

Example Code:

$key = "anotherpassword1";
$str = "does it work 12";

// MCRYPT with PKCS#7 padding
$iv = str_repeat("", 8); // Dummy IV for ECB
$enc = mcrypt_encrypt(MCRYPT_BLOWFISH, $key, $str."", MCRYPT_MODE_ECB, $iv);

// OpenSSL with PKCS#7 padding
$enc = openssl_encrypt($str, 'bf-ecb', $key, true);

// Decrypt with OpenSSL (requires re-encryption)
// $dec = openssl_decrypt($enc, 'bf-ecb', $key, true);
// echo var_dump($dec);

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