elgamal dec

elgamal decryption

from libnum import *
import re

print "Breaking Elgamal Cipher using known Plain-Text..."

p=234234
g=2342
y=1234

plain_c2="known text"
c2=123414134
c4=123414	

print "(c1,c2) known plain-text, (c3,c4) not known, c1==c3 (factor) which mean they are all encrypted with the same randomness k"

plain = s2n(plain_c2.encode('utf16')[::-1])

yk = c2*invmod(plain,p)%p

print "the solution is=",re.sub(r'[^\x01-\x7f]',r'',n2s(invmod(yk,p)*c4%p)[::-1])