Implementation of digital signature using RSA

1. Crypto - https://pypi.python.org/pypi/pycrypto
2. gmpy2 - https://pypi.python.org/pypi/gmpy2

1. We take the user input for message
2. First, we generate two random prime numbers p and q of 512 bit length.
3. We calculate n = p * q
4. We calculate Φ(n) = p-1 * q-1
5. We calculate e, such that gcd(e, Φ(n)) = 1
6. We calculate d, such that e * d = 1 mod Φ(n)
7. We calculate the message digest using SHA-224, M
8. We encrypt the message digest using senders public key CT = M^d mod n.
9. We send the M+S to receiver and (e, n) is made known to public.

1. We first separate the message from encrypted message digest
2. We then decrypt the message digest using sender public key S'= M^e mod n.
3. We then calculate the message digest of the message using SHA-224, M'
4. If M' = S', then the sender is indeed the real sender and the message is not been tampered with.