playfair.py

def matrix(key):
	matrix=[]
	for e in key.upper():
		if e not in matrix:
			matrix.append(e)
	alphabet="ABCDEFGHIKLMNOPQRSTUVWXYZ"
	
	for e in alphabet:
		if e not in matrix:
			matrix.append(e)	
	
	#initialize a new list. Is there any elegant way to do that?
	matrix_group=[]
	for e in range(5):
		matrix_group.append('')

	#Break it into 5*5
	matrix_group[0]=matrix[0:5]
	matrix_group[1]=matrix[5:10]
	matrix_group[2]=matrix[10:15]
	matrix_group[3]=matrix[15:20]
	matrix_group[4]=matrix[20:25]
	return matrix_group

def message_to_digraphs(message_original):
	#Change it to Array. Because I want used insert() method
	message=[]
	for e in message_original:
		message.append(e)

	#Delet space
	for unused in range(len(message)):
		if " " in message:
			message.remove(" ")

	#If both letters are the same, add an "X" after the first letter.
	i=0
	for e in range(len(message)/2):
		if message[i]==message[i+1]:
			message.insert(i+1,'X')
		i=i+2

	#If it is odd digit, add an "X" at the end
	if len(message)%2==1:
		message.append("X")
	#Grouping
	i=0
	new=[]
	for x in xrange(1,len(message)/2+1):
		new.append(message[i:i+2])
		i=i+2
	return new

def find_position(key_matrix,letter):
	x=y=0
	for i in range(5):
		for j in range(5):
			if key_matrix[i][j]==letter:
				x=i
				y=j

	return x,y

def encrypt(message):
	message=message_to_digraphs(message)
	key_matrix=matrix(key)
	cipher=[]
	for e in message:
		p1,q1=find_position(key_matrix,e[0])
		p2,q2=find_position(key_matrix,e[1])
		if p1==p2:
			if q1==4:
				q1=-1
			if q2==4:
				q2=-1
			cipher.append(key_matrix[p1][q1+1])
			cipher.append(key_matrix[p1][q2+1])		
		elif q1==q2:
			if p1==4:
				p1=-1;
			if p2==4:
				p2=-1;
			cipher.append(key_matrix[p1+1][q1])
			cipher.append(key_matrix[p2+1][q2])
		else:
			cipher.append(key_matrix[p1][q2])
			cipher.append(key_matrix[p2][q1])
	return cipher

def cipher_to_digraphs(cipher):
	i=0
	new=[]
	for x in range(len(cipher)/2):
		new.append(cipher[i:i+2])
		i=i+2
	return new


def decrypt(cipher):	
	cipher=cipher_to_digraphs(cipher)
	key_matrix=matrix(key)
	plaintext=[]
	for e in cipher:
		p1,q1=find_position(key_matrix,e[0])
		p2,q2=find_position(key_matrix,e[1])
		if p1==p2:
			if q1==4:
				q1=-1
			if q2==4:
				q2=-1
			plaintext.append(key_matrix[p1][q1-1])
			plaintext.append(key_matrix[p1][q2-1])		
		elif q1==q2:
			if p1==4:
				p1=-1;
			if p2==4:
				p2=-1;
			plaintext.append(key_matrix[p1-1][q1])
			plaintext.append(key_matrix[p2-1][q2])
		else:
			plaintext.append(key_matrix[p1][q2])
			plaintext.append(key_matrix[p2][q1])

	for unused in range(len(plaintext)):
		if "X" in plaintext:
			plaintext.remove("X")
	
	output=""
	for e in plaintext:
		output+=e
	return output.lower()

#key="cipher"
#message="effecttreecorrectapple"
#cipher="FNNFHOODPZCIVGFCHOBIBSPZ"

#key="playfairexample"
#message="Hide the gold in the tree stump"
#>>BMODZBXDNABEKUDMUIXMMOUVIF


print "Playfair Cipher"
order=input("Choose :\n1,Encrypting \n2,Decrypting\n")
if order==1:
	key=raw_input("Please input the key : ")
	message=raw_input("Please input the message : ")
	print "Encrypting: \n"+"Message: "+message
	print "Break the message into digraphs: "
	print message_to_digraphs(message)
	print "Matrix: "
	print matrix(key) 
	print "Cipher: " 
	print encrypt(message)
elif order==2:
	key=raw_input("Please input the key : ")
	cipher=raw_input("Please input the cipher text: ")
	#cipher="ILSYQFBWBMLIAFFQ"
	print "\nDecrypting: \n"+"Cipher: "+cipher
	print "Plaintext:"
	print decrypt(cipher)
else:
	print "Error"