Diffie-Hellman Key Agreement
Run locally
For compilation, the miracl library has been used. The compiled .a file and header files have been included but in case they don't work for your system. Please follow this guide to install miracl yourself.
gcc server.c -o server -I ./include libmiracl.a
gcc client.c -o client -I ./include libmiracl.aThen run ./server and ./client on two separate terminals.
Walkthrough
We have implemented a client-server setup where the client acts as Alice, and server acts as another person Bob. Both of them know the public part of the keys p and g. p has been pre-defined in the code as large 1024 bit prime but can be easily changed and g is 3.
Now we start running our server and the client attempts to connect to it.
Client Process (Alice):
Server Process (Bob):
Now, just press enter on the Client(Alice) terminal to initiate the process.
Alice generates a 160 bit random number a and uses it to generate Pa = 3^a % p. Then sends it to Bob.
Bob recieves Pa and at the same time, Bob generates a 160 bit random number b and uses it to generate Pb = 3^b % p. Then sends it to Alice.
Client Process (Alice):
Server Process (Bob):
Then Alice and Bob use these to find the common key.
For Alice: Key = Pb^a % p
For Bob: Key = Pa^b % p
Client Process (Alice):
Server Process (Bob):
As you can see, Alice and Bob have managed to achieve the same common key without using a KDC.