How can I encrypt with AES in C# so I can decrypt it in PHP?

Question

I\'ve found a few answers to Encrypt in PHP, and Decrypt in C#, but as yet have been unable to reverse the process...

The background is I want to:

In C#: AES

Answer 1

Generally it only depends on selecting the right options on both sides:

• Plaintext character format

  how plaintext characters are encoded in the bit string

• Padding

  how to pad the plaintext to be an exact multiple of the block size

• Key length

  must be agreed if there is a choice

• Key derivation

  how to create the bit string to be used for the key

• Mode

  which mode of encryption to use

• Storage format

  how we store the ciphertext

Please see here for a lot of information about these things. Especially the padding seems to be the root of most interoperability problems as PHP's mcrypt uses a NULL-padding by default and has no built-in support for any other padding mode, while e.g. .NET doesn't even provide an option to use a NULL-padding (as it may cause issues when encrypting binary data).