AES interoperability between .Net and iPhone?

At the very least, you are using differing initialization vectors (IV).

• The .Net code uses the key for IV.

  private static AesCryptoServiceProvider GetProvider(byte[] key)
  {
      //Set up the encryption objects
      AesCryptoServiceProvider result = new AesCryptoServiceProvider();
      byte[] RealKey = Encryptor.GetKey(key, result);
      result.Key = RealKey;
      result.IV = RealKey;
      return result;
  }

  and

  private static byte[] GetKey(byte[] suggestedKey, AesCryptoServiceProvider p)
  {
      byte[] kRaw = suggestedKey;
      List kList = new List();
      for (int i = 0; i < p.LegalKeySizes[0].MinSize; i += 8 )
      {
          kList.Add(kRaw[i % kRaw.Length]);
      }
      byte[] k = kList.ToArray();
      return k;
  }

  which should probably be: kList.Add(kRaw[(i / 8) % kRaw.Length]);. Otherwise a key whose length % 8 == 0 will use the same letter repeatedly, doh!

  Thus the IV (and key) used by .Net is: hleolhleolhleolh. This is not part of the API, but rather due to the wrapper code that you pointed at (which has a serious bug in it…).

• The iPhone code uses 0 for IV.

  // Initialization vector; dummy in this case 0's.
  uint8_t iv[kChosenCipherBlockSize];
  memset((void *) iv, 0x0, (size_t) sizeof(iv));

• openssl by default prepends a randomly generated salt (which is why the output is longer!).

The openssl output is more secure since it is prepending a random initialization vector. It looks like the first few bytes of the base64 decoded string is “Salted__”. You can also ask openssl to not use a salt (-nosalt) and / or provide an IV (-iv).

Essentially, openssl, .Net, and the iPhone are using the same encryption, you just need to be careful how you initialize the APIs with the encryption key and the initialization vector.