PKCS7.py

# Reference https://gist.github.com/chrix2/4171336

import binascii
import StringIO

class PKCS7Encoder(object):
    def __init__(self, k=16):
       self.k = k

    ## @param text The padded text for which the padding is to be removed.
    # @exception ValueError Raised when the input padding is missing or corrupt.
    def decode(self, text):
        '''
        Remove the PKCS#7 padding from a text string
        '''
        nl = len(text)
        val = int(binascii.hexlify(text[-1]), 16)
        if val > self.k:
            raise ValueError('Input is not padded or padding is corrupt')

        l = nl - val
        return text[:l]

    ## @param text The text to encode.
    def encode(self, text):
        '''
        Pad an input string according to PKCS#7
        '''
        l = len(text)
        output = StringIO.StringIO()
        val = self.k - (l % self.k)
        for _ in xrange(val):
            output.write('%02x' % val)
        return text + binascii.unhexlify(output.getvalue())

if __name__ == '__main__':
    encoder = PKCS7Encoder()
    padded_value = encoder.encode('thismessage')
    print padded_value.encode('hex')
    print encoder.decode(padded_value)