Diffie-Hellman Key Exchange
Diffie-Hellman Key Exchange, The protocol allows two users to exchange a secret key over an insecure medium without any prior secrets.
  • The Setup Suppose we have two people wishing to communicate: Alice and Bob
  • They do not want Eve (eavesdropper) to know their message.
  • Alice and Bob agree upon and make public two numbers g and p, where p is a prime and g is a primitive root mod p
 DH Parameter G : any BigInteger Value
 DH Parameter P : any BigInteger Value
             
Output

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Source https://security.stackexchange.com/questions/45963/diffie-hellman-key-exchange-in-plain-english

Diffie-Hellman is an algorithm used to establish a shared secret between two parties. It is primarily used as a method of exchanging cryptography keys for use in symmetric encryption algorithms like AES.

The algorithm in itself is very simple. Let's assume that Alice wants to establish a shared secret with Bob.

  1. Alice and Bob agree on a prime number, p, and a base, g, in advance. For our example, let's assume that p=23 and g=5.
  2. Alice chooses a secret integer a whose value is 6 and computes A = g^a mod p. In this example, A has the value of 8.
  3. Bob chooses a secret integer b whose value is 15 and computes B = g^b mod p. In this example, B has the value of 19.
  4. Alice sends A to Bob and Bob sends B to Alice.
  5. To obtain the shared secret, Alice computes s = B^a mod p. In this example, Alice obtains the value of s=2
  6. To obtain the shared secret, Bob computes s = A^b mod p. In this example, Bob obtains the value of s=2.

The algorithm is secure because the values of a and b, which are required to derive s are not transmitted across the wire at all.