Python实现换位加密

import  math
def     transpostionEncrypt(msg,key):#加密
        size = len(msg)
        result = []
        for i in range(key):
            t = i
            while t<size:
                result.append(msg[t])
                t+=key
        return ''.join(result)
def     transpostionDecrypt(msg,key):#解密
        numOfColums = int(math.ceil(len(msg)/float(key)))
        numOfRows = key
        sharedBox = numOfColums*numOfRows - len(msg)
        row = 0
        col = 0
        result = ['']*numOfColums
        for i in msg:
            result[col] += i
            col+=1
            if col==numOfColums or (col==numOfColums-1 and row>=numOfRows-sharedBox):
                col=0
                row+=1
        return ''.join(result)

def     main():

        cipher = transpostionEncrypt("Common sense is not so common.",8)
        print cipher#密文

        print transpostionDecrypt(cipher,8)
if      __name__=="__main__":
        main()