Chris,

I ran into your padding methods which put the remainder size in each empty space after the real data.

I have a problem with

ByteArray>>unpaddedSize

            "If I was padded by a BlockCipher, answer the size of the original plaintext."

            self isProperlyPadded ifFalse: [ CryptographyError signal: 'Authentication failure (improperly padded!)' ].

            ^ self size - self last

Since isProperlyPadded assumes that that was some padding the error seems unnecessary.

Shouldn’t this say:

ByteArray>>unpaddedSize

            "If I was padded by a BlockCipher, answer the size of the original plaintext."

            self isProperlyPadded ifFalse: [^self size].

            ^ self size - self last