cipher.py

class Cipher:
    def __init__(self):
        self.algorithm = ''
        self.key = None
    def set_algorithm(self, algo):
        self.algorithm=algo
    def set_key(self, key):
        self.key = key
    def crypt(self, buffer):
        enc=''
        if self.algorithm=='':
            return None
        elif self.algorithm=='Row-Transposition':
            """
                key : 123456
                plaintext: pythonchallenges
                step1:  123456
                        python
                        challe
                        nges
                step2:
                cipher -> pcnyhgtaehlsolne
            """
            l = len(self.key)
            __key = [int(e) for e in self.key]
            __key.sort()
            parts=[]
            for i in range(0, len(buffer), l):
                parts.append(buffer[i:i+l])
            for i in range(len(self.key)):
                index = self.key.index(str(__key[i]))
                for e in parts:
                    if len(e) < index+1:
                        continue
                    else:
                        enc+=e[index]
            return enc
        elif self.algorithm=='Rail-Fence-Transposition':
            n = 1 + len(buffer)/self.key
            matrix = ['']*self.key
            for i in range(len(buffer)):
                matrix[i%self.key]+=buffer[i]
            for i in range(self.key):
                enc+=matrix[i]
            return enc
        else:
            return None
C = Cipher()
C.set_algorithm('Row-Transposition')
C.set_key('123456')
print C.crypt('pythonchallenges')
C.set_algorithm('Rail-Fence-Transposition')
C.set_key(2)
print C.crypt('HELLOWORLD')