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 BobThey 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

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Diffie Helman Key Exchange

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.
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.
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.
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.
Alice sends A to Bob and Bob sends B to Alice.
To obtain the shared secret, Alice computes s = B^a mod p. In this example, Alice obtains the value of s=2
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.