ICS/ICS-07 at main · eyemnv/ICS · GitHub

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# Function to find gcd
# of two numbers
def euclid(m, n):

	if n == 0:
		return m
	else:
		r = m % n
		return euclid(n, r)


# Program to find
# Multiplicative inverse
def exteuclid(a, b):

	r1 = a
	r2 = b
	s1 = int(1)
	s2 = int(0)
	t1 = int(0)
	t2 = int(1)

	while r2 > 0:

		q = r1//r2
		r = r1-q * r2
		r1 = r2
		r2 = r
		s = s1-q * s2
		s1 = s2
		s2 = s
		t = t1-q * t2
		t1 = t2
		t2 = t

	if t1 < 0:
		t1 = t1 % a

	return (r1, t1)

p = int(input("Enter Values Of P :"))
q = int(input("Enter Values of Q :"))
n = p * q
Pn = (p-1)*(q-1)

# Generate encryption key
# in range 1<e<Pn
key = []

for i in range(2, Pn):

	gcd = euclid(Pn, i)

	if gcd == 1:
		key.append(i)


# Select an encryption key
# from the above list
e = int(313)

# Obtain inverse of
# encryption key in Z_Pn
r, d = exteuclid(Pn, e)
if r == 1:
	d = int(d)
	print("decryption key is: ", d)

else:
	print("Multiplicative inverse for\
	the given encryption key does not \
	exist. Choose a different encryption key ")


# Enter the message to be sent
M = input("Enter Message To Be Sent :")

# Signature is created by Alice
S = (M**d) % n

# Alice sends M and S both to Bob
# Bob generates message M1 using the
# signature S, Alice's public key e
# and product n.
M1 = (S**e) % n

# If M = M1 only then Bob accepts
# the message sent by Alice.

if M == M1:
	print("As M = M1, Accept the\
	message sent by Alice")
else:
	print("As M not equal to M1,\
	Do not accept the message\
	sent by Alice ")