RosettaCodeData/Task/RSA-code/Python/rsa-code-2.py

import random
import time

def decrypt(F,d):
    if d == 0:
        return 1
    if d == 1:
        return F
    w,r = divmod(d,2)
    if r == 1:
        return decrypt(F*F%n,w)*F%n
    else:
        return decrypt(F*F%n,w)

def correct():
    for i in range(len(C)):
        if len(str(P[i]))%2 !=0:
            y = str(0)+str(P[i])
            P.remove(str(P[i]))
            P.insert(i,y)

def cipher(b,e):
    if e == 0:
        return 1
    if e == 1:
        return b
    w,r = divmod(e,2)
    if r == 1:
        return cipher(b*b%n,w)*b%n
    else:
        return cipher(b*b%n,w)

def group(j,h,z):
    for i in range(int(j)):
        y = 0
        for n in range(h):
            y += int(numP[(h*i)+n])*(10**(z-2*n))
        X.append(int(y))

def gcd(a, b):
        while b != 0:
            (a, b) = (b, a%b)
        return a



letter = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q",
          "r","s","t","u","v","w","x","y","z",",",".","!","?"," "]
number = ["01","02","03","04","05","06","07","08","09","10","11","12","13",
          "14","15","16","17","18","19","20","21","22","23","24","25","26","27",
          "28","29","30","31"]


print( '\n' )
def Decrypt():
    #decrypts an encoded message
    global m,P,C,x,h,p,Text,y,w
    P = []
    C = str(input("Enter ciphertext blocks:"))
    C = C.lstrip('[')
    C = C.rstrip(']')
    C = C.split(',')
    for i in range(len(C)):
        x = decrypt(int(C[i]),d)
        P.append(str(x))
    correct()
    #print(P)
    h = len(P[0])
    p = []
    for i in range(len(C)):
        for n in range(int(h/2)):
            p.append(str(P[i][(2*n):((2*n)+2)]))

    Text = []
    for i in range(len(p)):
        for j in range(len(letter)):
            if str(p[i]) == number[j]:
                Text.append(letter[j])
    PText = str()
    for i in range(len(Text)):
        PText = PText + str(Text[i])
    print("Plaintext is:", PText)

def Encrypt():
    #encrypts a plaintext message using the current key
    global plaintext,numP,q,j,z,X,C
    plaintext =(input("Enter Plaintext :"))
    plaintext = plaintext.lower()
    numP = []
    for i in range(len(plaintext)):
        for j in range(len(letter)):
            if plaintext[i] == letter[j]:
                numP.append(number[j])
    h = (len(str(n))//2)-1
    q = len(numP)%h
    for i in range(h-q):
        numP.append(number[random.randint(0,25)])
    j = len(numP) / h
    #print(numP)
    X = []
    z = 0
    for m in range(h-1):
        z+=2
    group(j,h,z)
    k = len(X)
    C = []
    for i in range(k):
        b = X[i]
        r = cipher(b,e)
        C.append(r)
    print("Ciphertext:",C)
    print("Number of Ciphertext blocks:",len(C))

def setup():
    global n,e,d
    while True:
        try:
            n = int(input(" Enter a value for n :"))
            if n > 2:
                break
        except ValueError:
            print('please enter a number')
    while 1!=2 :
        try:
            e = int(input(" Enter a value for e :"))
            if e >= 2:
                break
        except ValueError:
            print('please enter a number')
    while True:
        try:
            d = int(input(" Enter a value for d. If d unknown, enter 0 :"))
            if d >= 0:
                break
        except ValueError:
            print('please enter a number')

#setup()
n = 2537
e = 13
d = 937

print("To redefine n,e, or d, type 'n','e',... etc.")
print("To encrypt a message with the current key, type 'Encrypt'")
print("To decrypt a message with the current key, type 'Decrypt'")
print("Type quit to exit")
print( '\n' )
print( '\n' )

mm = str()
while mm != 'quit':
    mm = input("Enter Command...")
    if mm.lower() == 'encrypt':
        Encrypt()
    elif mm.lower() == 'decrypt':
        Decrypt()
    elif mm.lower() == 'n':
        try:
            print('current n = ',n)
            n = int(input(" Enter a value for n :"))
        except ValueError:
            print('That is not a valid entry')
    elif mm.lower() == 'help':
        print("To redefine n,e, or d, type 'n','e',... etc.")
        print("To encrypt a message with the current key, type 'Encrypt'")
        print("To decrypt a message with the current key, type 'Decrypt'")
        print("Type quit to exit")
        print( '\n' )
        print( '\n' )
    elif mm.lower() == 'e':
        try:
            print('current e = ',e)
            e = int(input(" Enter a value for e :"))
        except ValueError:
            print('That is not a valid entry')
    elif mm.lower() == 'd':
        try:
            print('current d = ',d)
            d = int(input(" Enter a value for d :"))
        except ValueError:
            print('That is not a valid entry')
    else:
        if mm != 'quit':
            ii= random.randint(0,6)
            statements = ["I sorry, Dave. I'm afraid i can't do that","I'm begging you....read the directions","Nah ahh ahh, didnt say the magic word","This input is....UNACCEPTABLE!!","Seriously....was that even a word???","Please follow the directions","Just type 'help' if you are really that lost"]
            print(statements[ii])