JavaExercism/exercises/diffie-hellman

Diffie Hellman

Diffie-Hellman key exchange.

Alice and Bob use Diffie-Hellman key exchange to share secrets. They start with prime numbers, pick private keys, generate and share public keys, and then generate a shared secret key.

Step 0

The test program supplies prime numbers p and g.

Step 1

Alice picks a private key, a, greater than 1 and less than p. Bob does the same to pick a private key b.

Step 2

Alice calculates a public key A.

A = g**a mod p

Using the same p and g, Bob similarly calculates a public key B from his private key b.

Step 3

Alice and Bob exchange public keys. Alice calculates secret key s.

s = B**a mod p

Bob calculates

s = A**b mod p

The calculations produce the same result! Alice and Bob now share secret s.

Java Tips

Hints

This exercise requires you to perform calculations on large numbers. To correctly represent large numbers, the BigInteger class is used.

Running the tests

You can run all the tests for an exercise by entering

$ gradle test

in your terminal.

Source

Wikipedia, 1024 bit key from www.cryptopp.com/wiki. http://en.wikipedia.org/wiki/Diffie%E2%80%93Hellman_key_exchange

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.