CA 304 - Networks Project 2008/2009 Implement Diffie

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CA 304 - Networks Project 2008/2009
Implement Diffie-Hellman Key Exchange
Bis FORBEN
David DUPEYRON
CA 304 – Network Project
Diffie-Hellman Key Exchange
Bis Forben
David Dupeyron
Introduction :
The aim of this project is to write a program able to make communicate
two computers with secure conversation using a key exchange.
First of all, we have to write a single source code, divided in two principal files:
a server and a client.
Then, we need to implement the “Diffie-Hellman Key Exchange” in order to
have a secure communication with different keys generated on each different
execution of the code.
Network part:
To communicate between a client and a server, we must create a socket,
which is the constant connection between two programs or computers.
A socket is essentially an end point in a communications session, a program can
send and receive TCP/IP messages by opening a socket and reading and writing
data to and from the socket. This simplifies program development because the
programmer needs to worry only about manipulating the socket and can rely on
the operating system to actually transport messages across the network correctly.
Actually a socket address on a device is the TCP/UDP port number plus the IP
network.
So we have to launch the server at first, which is listening on the port which
writes as an argument (allows you to change it in an easy way) until the client is
launched.
We did not encounter a lot of problems in this part, besides that the server closed
the connection after having received the first message, which solved the trouble
with a boucle.
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CA 304 – Network Project
Diffie-Hellman Key Exchange
Bis Forben
David Dupeyron
Cryptographic part:
The Diffie-Hellman key exchange is a cryptographic protocol which
permits to create a secure connection between a client and a server, using a
secret calculated key.
The calculation and the exchange of the key between “Alice” and “Bob” are
made as follows:
http://fr.wikipedia.org/wiki/Diffie-Helman
Alice and Bob use a secret and different integer (a and b), and use a same prime
number (p) and a same base (g).
And with this system, they will get the same Key (K) and a third person called
Eve has no way to find out this key.
This symmetric key cipher is an easy way to encrypt a communication.
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