rc6_v2.py

import math
import sys

#rotate right input x, by n bits
def ROR(x, n, bits = 32):
    mask = (2**n) - 1
    mask_bits = x & mask
    return (x >> n) | (mask_bits << (bits - n))

#rotate left input x, by n bits
def ROL(x, n, bits = 32):
    return ROR(x, bits - n,bits)

#convert input sentence into blocks of binary
#creates 4 blocks of binary each of 32 bits.
def blockConverter(sentence):
    encoded = []
    res = ""
    for i in range(0,len(sentence)):
        if i%4==0 and i!=0 :
            encoded.append(res)
            res = ""
        temp = bin(ord(sentence[i]))[2:]
        if len(temp) <8: 
            temp="0" *(8-len(temp)) + temp
            res=res + temp
            encoded.append(res)
            return encoded
            #converts 4 blocks array of long int into string
            def deBlocker(blocks):
            s=""
            for ele in blocks:
                temp=bin(ele)[2:]
                if len(temp) <32:
                    temp = "0"*(32-len(temp)) + temp
        for i in range(0,4):
            s=s+chr(int(temp[i*8:(i+1)*8],2))
    return s

#generate key s[0... 2r+3] from given input string userkey
def generateKey(userkey):
    r=12
    w=32
    b=len(userkey)
    modulo = 2**32
    s=(2*r+4)*[0]
    s[0]=0xB7E15163
    for i in range(1,2*r+4):
        s[i]=(s[i-1]+0x9E3779B9)%(2**w)
    encoded = blockConverter(userkey)
    #print encoded
    enlength = len(encoded)
    l = enlength*[0]
    for i in range(1,enlength+1):
        l[enlength-i]=int(encoded[i-1],2)

    v = 3*max(enlength,2*r+4)
    A=B=i=j=0

    for index in range(0,v):
        A = s[i] = ROL((s[i] + A + B)%modulo,3,32)
        B = l[j] = ROL((l[j] + A + B)%modulo,(A+B)%32,32)
        i = (i + 1) % (2*r + 4)
        j = (j + 1) % enlength
    return s

def encrypt(sentence,s):
    encoded = blockConverter(sentence)
    enlength = len(encoded)
    A = int(encoded[0],2)
    B = int(encoded[1],2)
    C = int(encoded[2],2)
    D = int(encoded[3],2)
    orgi = []
    orgi.append(A)
    orgi.append(B)
    orgi.append(C)
    orgi.append(D)
    r=12
    w=32
    modulo = 2**32
    lgw = 5
    B = (B + s[0])%modulo
    D = (D + s[1])%modulo
    for i in range(1,r+1):
        t_temp = (B*(2*B + 1))%modulo
        t = ROL(t_temp,lgw,32)
        u_temp = (D*(2*D + 1))%modulo
        u = ROL(u_temp,lgw,32)
        tmod=t%32
        umod=u%32
        A = (ROL(A^t,umod,32) + s[2*i])%modulo
        C = (ROL(C^u,tmod,32) + s[2*i+ 1])%modulo
        (A, B, C, D)  =  (B, C, D, A)
    A = (A + s[2*r + 2])%modulo
    C = (C + s[2*r + 3])%modulo
    cipher = []
    cipher.append(A)
    cipher.append(B)
    cipher.append(C)
    cipher.append(D)
    return orgi,cipher


def decrypt(esentence,s):
    encoded = blockConverter(esentence)
    enlength = len(encoded)
    A = int(encoded[0],2)
    B = int(encoded[1],2)
    C = int(encoded[2],2)
    D = int(encoded[3],2)
    cipher = []
    cipher.append(A)
    cipher.append(B)
    cipher.append(C)
    cipher.append(D)
    r=12
    w=32
    modulo = 2**32
    lgw = 5
    C = (C - s[2*r+3])%modulo
    A = (A - s[2*r+2])%modulo
    for j in range(1,r+1):
        i = r+1-j
        (A, B, C, D) = (D, A, B, C)
        u_temp = (D*(2*D + 1))%modulo
        u = ROL(u_temp,lgw,32)
        t_temp = (B*(2*B + 1))%modulo
        t = ROL(t_temp,lgw,32)
        tmod=t%32
        umod=u%32
        C = (ROR((C-s[2*i+1])%modulo,tmod,32)  ^u)
        A = (ROR((A-s[2*i])%modulo,umod,32)   ^t)
    D = (D - s[1])%modulo
    B = (B - s[0])%modulo
    orgi = []
    orgi.append(A)
    orgi.append(B)
    orgi.append(C)
    orgi.append(D)
    return cipher,orgi





def main():

    key='A WORD IS A WORD'
    sentence = 'I WORD IS A WORD'

    sentence =sentence + " "*(16-len(sentence))
    key =key + " "*(16-len(key))

    key = key[:16]

    print("Key:\t"+key)
    s = generateKey(key)

    sentence = sentence[:16]

    orgi,cipher = encrypt(sentence,s)
    esentence = deBlocker(cipher)

    print("Input:\t "+sentence)

    print("\nOriginal String list: ",orgi)
    print("Length of Input String: ",len(sentence))

    print("\nEncrypted String list: ",cipher)
    print("Encrypted String: " + esentence)
    print("Length of Encrypted String: ",len(esentence))

    cipher,orgi = decrypt(esentence,s)
    sentence = deBlocker(orgi)
    print("\nDecrypted:\t",sentence)

if __name__ == "__main__":
	main()