8.TransCipher.py

ENC = 0
DEC = 1


def parseKey(key):
	tmp = []
	key = key.upper()
	
	for i, k in enumerate(key):
		tmp.append((i, k))
		
	tmp = sorted(tmp, key=lambda x:x[1])	
	
	enc_table = {}
	dec_table = {}
	for i, r in enumerate(tmp):
		enc_table[r[0]] = i
		dec_table[i] = r[0]
	
	return enc_table, dec_table


def transposition(msg, key, mode):
	msgsize = len(msg)
	keysize = len(key)	
	ret = ''
	
	filler = ''	
	if msgsize%keysize != 0:
		filler = '0'*(keysize - msgsize%keysize)	
			
	msg = msg.upper()
	msg += filler
	
	enc_table, dec_table = parseKey(key)
	
	if mode == ENC:
		table = enc_table
	else:
		table = dec_table
	
	if mode == ENC:
		buf = ['']*keysize
		for i, c in enumerate(msg):
			col = i%keysize
			index = table[col]
			buf[index] += c
			
		for text in buf:
			ret += text
		
	else:
		blocksize = int(msgsize/keysize)
		buf = ['']*keysize
		
		pos = 0		
		for i in range(keysize):
			text = msg[pos:pos+blocksize]
			index = table[i]
			buf[index] += text
			pos += blocksize			
		
		for i in range(blocksize):
			for j in range(keysize):
				if buf[j][i] != '0':
					ret += buf[j][i]	
		
	return ret
	
def main():
	key = 'BRAIN'	
	msg = 'TREASUREBOXISBURRIEDATTWOHUNDREDFEETTONORTHEASTAWAYFROMYOURHOME'
	print('Original:\t\t%s' %msg.upper())

	ciphertext = transposition(msg, key, ENC)
	print('Ciphered:\t\t%s' %ciphertext)
	
	deciphertext = transposition(ciphertext, key, DEC)
	print('Deciphered:\t%s' %deciphertext)


if __name__ == '__main__':
	main()