BasePadding to remove padding instead of 'take'ing it

[CaringDev]

The following test currently fails:

      var data = Uint8List.fromList([1, 2, 3, 3, 3]);
      final pkcs7 = PKCS7Padding()..init();
      final padCount = pkcs7.padCount(data);
      expect(padCount, 3);
      final d = pkcs7.process(false, data);
      // fails, length is 3
      expect(d.length, data.length - padCount);

As far as I can tell, there is no process function in the original Java implementation: see PKCS7Padding and BlockCipherPadding

I'm not sure this is a safe change, as it might negatively affect other paddings.

[mwcw]

Hi,

I think what has happened is that this method was added and lost over time.

Padding is added and removed by PaddedBlockCipher which does not call this method.

Interestingly enough that process method in BasePadding cannot add padding because it is not suppled with a final length to pad up to or a block size for example.

I replaced the body of the method with a throw and it was never called by any of the tests.

If it is being used by anyone I don't know what for to be honest.

I'll merge this in but I have added an exception if pad is true.

Thanks for the submission!

MW