Question

I have an Android application, which uses javax.crypto to encrypt some text data in files. Encryption implementation is similar to this. The application works fine with the encrypted data it previously created.

Now, I almost ported my Android application to desktop (JFace/SWT). I’m using the same encryption implementation for the ported application, as it does not depend on any Android-specific API. The ported application works fine with encrypted data it created.

The problem is that desktop application cannot decrypt data, which was saved with Android application. The Android application fails to decrypt data, which was saved with desktop application as well. I double checked bytes streams of plain data and password to encrypt on both platforms. They are the same, so there are no problems with text encoding or so. But encryption routine return different encrypted results on different platforms even input data is byte-to-byte identical.

Does Java crypto API guarantees the same operation on different platforms? Should an encryption provider (AES/128bit in my case) work the same way on Android, Linux and Windows? Is there a way to tune javax.crypto to get interoperability on different platforms?

Answer 1

AES-128 should work the same on both systems. In theory.

In practice there are a lot of details that need to be the same on both systems.

• are you using the same padding at both sides?
• are you using the same mode (CBC, CTR, ECB) at both sides?
• do you have exactly the same password at both sides?
• do you have the same IV/Nonce at both sides?
• do you have the same key derivation method on both sides?

Check any defaults on both systems. If the defaults don’t match then you will need to set one side or the other explicitly.