Diffie-Hellman Algorithm in Java4 min read

Diffie-Hellman is a way of generating a shared secret between two people in such a way that the secret can’t be seen by observing the communication.That’s an important distinction: You’re not sharing information during the key exchange, you’re creating a key together.

Diffie-Hellman algorithm is one of the most important algorithms used for establishing a shared secret. At the time of exchanging data over a public network, we can use the shared secret for secret communication. We use an elliptic curve for generating points and getting a secret key using the parameters.

  1. We will take four variables, i.e., P (prime), G (the primitive root of P), and a and b (private values).
  2. The variables P and G both are publicly available. The sender selects a private value, either a or b, for generating a key to exchange publicly. The receiver receives the key, and that generates a secret key, after which the sender and receiver both have the same secret key to encrypt.

Let’s understand the process step by step for user1 (sender) and user2 (receiver):

1.P, G => available public keys.P, G => available public keys.
2.a is selected as a private key.b is selected as a private key.
3.Eq. to generate key:
x=Ga modP
Eq. to generate key:
y=Gb modP
4.After exchanging keys, user1 receives key y.After exchanging keys, user2 receives key x.
5.User1 generates a secret key by using the received key y:
ka=ya modP
User2 generates a secret key by using the received key x:
kb=xb modP

Algebraically, 5th step can be shown as follows:

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