#!/usr/bin/python2

import hashlib, getpass, random, argparse, json, sys

p = 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

prompt = getpass.getpass
# If you want the password prompt to be in the clear, uncomment this next line.
#prompt = raw_input

try:
    import gmpy
    assert gmpy.is_prime(p) and gmpy.is_prime(p // 2)
except:
    print "Couldn't verify primality!"

if len(sys.argv) != 2 or sys.argv[1] not in ("1", "2"):
    print "Usage: %s [1|2]" % sys.argv[0]
    print
    print "For the first phase of SPEKE, run with argument 1."
    print "This will write out a file ./secrets"
    print "For the second phase, run with the path to ./secrets as an argument."
    exit(1)

if sys.argv[1] == "1":
    password  = prompt("        Entropy: ")
    password2 = prompt("Entropy (again): ")
    assert password == password2
    g = int(hashlib.sha512(password).hexdigest(), 16)
    a = random.SystemRandom().randint(1, p)
    with open("secrets", "w") as f:
        print >>f, json.dumps({"g": g, "a": a}, indent=2)
    ga = pow(g, a, p)
    print
    print "g^a = 0x%x" % ga
else:
    with open("secrets") as f:
        secrets = json.load(f)
    gb = input("Other party's g^a: ")
    gab = pow(gb, secrets["a"], p)
    symmetric_secret = hashlib.sha512(str(gab)).hexdigest()[:32]
    confirmation = hashlib.sha512(symmetric_secret).hexdigest()[:32]
    print "Symmetric secret:", symmetric_secret
    print "Confirmation:", confirmation