m2crypto aes-256-cbc not working against encoded openssl files.

Question

$ echo 'this is text' > text.1
$ openssl enc -aes-256-cbc -a -k "thisisapassword" -in text.1 -out text.enc
$ openssl enc -d -aes-256-cbc -a -k "thisisapassword" -in text.enc -out text.2
$ cat text.2
this is text

I can do this with openssl. Now, how do I do the same in m2crypto. Documentation is lacking this. I looked at the snv test cases, still nothing there. I found one sample, http://passingcuriosity.com/2009/aes-encryption-in-python-with-m2crypto/ (changed to aes_256_cbc), and it will encrypted/descrypt it's own strings, but it cannot decrypt anything made with openssl, and anything it encrypts isn't decryptable from openssl.

I need to be able enc/dec with aes-256-cbc as have many files already encrypted with this and we have many other systems in place that also handle the aes-256-cbc output just fine.

We use password phrases only, with no IV. So setting the IV to \0 * 16 makes sense, but I'm not sure if this is also part of the problem.

Anyone have any working samples of doing AES 256 that is compatible with m2crypto?

I will also be trying some additional libraries and seeing if they work any better.

Answer 1

Part of the problem is that the openssl created file contains 16 bytes of prepended salt information Salted__xxxxxxxx. So, these must be extracted first, then decryption may occur. The next problem is to take original password, sprinkle in the salt, and take the generated key from that and make the key/iv pair for decryption. I have been able to make the first round of they key in hash, but being 256 bit, it needs two rounds to be successful. The problem is creating the second round of hash.

It should also be mentioned that we are locked into python 2.4 so some of the future key routines that are introduced do not work for us.