# Diffie Hellman Key exchange algorithm Implementation in C

## Diffie Hellman algorithm is a public-key algorithm used to establish a shared secret that can be used for secret communications while exchanging data over a public network.

### It is primarily used as a method of exchanging cryptography keys for use in symmetric encryption algorithms. It was Proposed in 1976 by Whitfield Diffie and Martin Hellman. Diffie-Hellman is currently used in many protocols like Secure Sockets Layer (SSL)/Transport Layer Security (TLS), Secure Shell (SSH), Internet Protocol Security (IPSec), Public Key Infrastructure (PKI).

#### Steps of Diffie Hellman key exchange Algorithm

1.      Requires two large numbers, one prime (P), and (G), a primitive root of P
2.      P and G are both publicly available numbers
a.       P is at least 512 bits
3.      Users pick private values a and b
4.      Compute public values
a.       x = ga mod p
b.      y = gb mod p
5.      Public values x and y are exchanged
6.      Compute shared, private key
a.       ka = yamod p
b.      kb = xbmod p
c.       Algebraically it can be shown that ka = kb

Users now have a symmetric secret key to encrypt.

#### Example

1. Alice and Bob get public numbers
1. P = 23, G = 9
2. Alice and Bob compute public values
3. X = 94 mod 23 = 6561 mod 23 = 6
4. Y = 93 mod 23 = 729 mod 23    = 16
5. Alice and Bob exchange public numbers
2. Alice and Bob compute symmetric keys
1. ka = ya mod p = 164 mod 23 = 9
2. kb = xb mod p = 63 mod 23 = 9
3.       9 is the shared secret.

#### RSA Algorithm(Encryption and Decryption) implementation in C

Diffie Hellman algorithm is a public-key algorithm used to establish a shared secret that can be used for secret communications while exchanging data over a public network. It is primarily used as a method of exchanging cryptography keys for use in symmetric encryption algorithms. Diffie Hellman Key exchange algorithm Implementation in C