padding/unpadding per PKCS7 or PKCS5.

pkcs7.py

# padding/unpadding per PKCS7 or PKCS5.

class PKCS7(object):
	def __init__(self, block_size):
		self.block_size = block_size

	def pad(self, string):
		padding_number = self.block_size - len(string) % self.block_size
		if padding_number == self.block_size:
			return string
		padding = chr(padding_number) * padding_number
		return string + padding

	def unpad(self, string):
		if not string: return string
		if len(string) % self.block_size:
			raise TypeError('string is not a multiple of the block size.')
		padding_number = ord(string[-1])
		if padding_number >= self.block_size:
			return string
		else:
			if all( padding_number == ord(c) for c in string[-padding_number:] ):
				return string[0:-padding_number]
			else:
				return string