Tracks
/
C#
/
Exercises
/
Diffie-Hellman

# Diffie-Hellman

Medium

## Instructions

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 = gáµƒ 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 = Báµƒ mod p
``````

Bob calculates

``````s = Aáµ‡ mod p
``````

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

This exercise requires you to perform calculations on large numbers. To correctly represent large numbers, the [BigInteger](https://docs.microsoft.com/en-us/dotnet/api/system.numerics.biginteger

Edit via GitHub