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phpencryptionmcryptphp-openssl

Rijndael 192-bit block size mcrypt alternative

Please read this question before knee-jerking it as a duplicate (although if it actually is, not sure why I couldn't find it, but GREAT!!)

We have been using mcrypt with the rijndael-192 module in cfb mode for years now. We have a LOT of stuff encrypted with it.

PHP 7.2 which we HAVE to move to, no longer includes mcrypt.

Openssl AES does not support 192 block sizes(or anything other than 128). So moving forward I will be changing the symmetric encryption.

The problem I have is with the legacy data, I cannot see how to decrypt it going forward without mcrypt. There is no option of modifying the legacy data as that would be unfeasible for us.

So my question is, how do I decrypt my data that has been encrypted using rijndael with 192 block size, without mcrypt?

Thanks

Solution

  • Thought I should report back as I hate it when questions are left hanging.

    I have found no other way to decrypt a Rijndael(AES) cipher using a 192 block size within PHP, other than using the mcrypt library. I had two options:

    1. Install mcrypt in PHP 7.2 from the PHP PECL extension repository and continue using it.
    2. Decrypt my data in PHP 7.1 using the mcrypt library, and re-encrypt using openssl AES cipher with 128 block sizes.

    We opted for option 2. Although it was slow and painful, moving away from mcrypt was clearly the better long term solution.