Bouncycastle PBEWITHSHA256AND256BITAES-CBC-BC Javascript implementation

Question

I've tried but failed to encode a string in Javascript to decode on a java server. We'd like to use the bouncycastle algorithm PBEWITHSHA256AND256BITAES-CBC-BC to decode serverside.

I've tried using crypto.js to do the encoding using the following code:

  var encrypted = Crypto.AES.encrypt("it was Professor Plum in the library with the candlestick", 
        key, 
        { mode: new Crypto.mode.CBC });

   var encryptedString = Crypto.util.bytesToHex(Crypto.charenc.Binary.stringToBytes(crypted));

However this doesn't decode correctly on the server, my guess is its something to do with the SHA256 but I can't work out what it would be digesting & can't find any documentation. Does anyone know how to perform the encryption in javascript?

Answer 1

You need to do everything the same at both ends. You need the same key. You need the same mode (CBC) you need the same padding (use PKCS7) and you need the same IV.

Check that the actual key you are using is the same at both ends by displaying the hex, after you have run the passphrase through SHA-256. Check the hex for the IVs as well. Don't use any defaults, but explicitly pick the mode and padding to use.

If you think that it is the PBE/SHA-256 that is going wrong then you might want to look at how your text passphrase is being turned into bytes. Again, check the hex at both sides before it is passed to SHA-256. Converting text to bytes is a common source of errors. You need to be very sure what stringToBytes() is doing and that whatever you are using on the Java side is doing exactly the same.