#sets the mod to 26
for i in range(26):
#Prints the plain text alphabet and it's corresponding ciphertext alphabet values
#Note: ascii A is 65, so we have to add/sub 65 to account for ascii value (so that A is essentialy set to 0)
print chr(i+65) + ": " + chr(((a*i+b)%26)+65)

print "Now that we have the transposition table, let's encrypt a plaintext message\n"

#User inputs the plain text message they want encrypted
plaintext = raw_input("Message (in capitals):")
# Start with and empty list for the encrypted message
ciphertext = []

#Finds the numerical value for each letter in the plain text and puts it in the list
for x in plaintext:
ciphertext.append(ord(x))

#Append the corresponding plain text character to encrypted one
for i in range(len(ciphertext)):
#encryption algorithm
ciphertext[i] = chr(((a*(ciphertext[i]-65)+b)%26)+65)

#Print the original and the encrypted message
print plaintext + ": " + " ".join(ciphertext)

#Decryption Function
#D(x) = daffine = ainverse *(x-b) mod m
def daffine(a, b):
print "This is the decrypted Alphabet\n (cipher text : plain text)"

#sets the mod to 26
for i in range(26):
#Finds the modular multiplicative inverse of a, which is needed in the function below for decrypting
ainverse = a**(phi(a)-1)%26
#Prints the cipher text alphabet and it's corresponding plain text alphabet values
print chr(i+65) + ": " + chr((ainverse*(i- b))%26+65)

print "Now that we have the transposition table, let's decipher that message\n"

#User inputs the ciphertext they want decrypted
ciphertext =raw_input("Enter encrypted message (in capitals): ")
# Start with and empty list to store the decrypted message
plaintext = []

#Finds the numerical value for letter in the ciphertext and puts it in the list
for x in ciphertext:
plaintext.append(ord(x))

#Append the corresponding ciphertext character to plain text
for i in range(len(plaintext)):
#decryption algorithm
plaintext[i] = chr((ainverse*((plaintext[i]-65)- b))%26+65)

#Print the cipher text and the decrypted message
print ciphertext + ": " + " ".join(plaintext) + '\n'

#Other Functions Needed for Decryption

#Greatest common divisor
def gcd(a,b):
#Return the gcd of two positive integers.
while b != 0:
a, b = b, a%b
print a
print b
return a

#Coprime
def coprime(a,b):
#return True if 'a' and 'b' are coprime.
return gcd(a,b) == 1

#Euler's Totient Function
def phi(m):
if m == 1:
return 1
else:
r = [n for n in range(1,int(m)) if coprime(int(m),int(n))]
#Returns the number/length of coprime numbers that make up m
return len(r)

print "Would you like to encrypt (enter e) or decrypt (enter d) the message? "
decision = raw_input("> ")

if decision == "e":
print "Enter the key: "
a = int(input("a key: "))
b = int(input("b key: "))
eaffine(a, b)

elif decision == "d":
print "Now that you have a secret message let's decipher it!"
print "Enter the key: "
a = int(input("a key: "))
b = int(input("b key: "))
daffine(a, b)

else:
print "I hope you liked the program!"