Diffie–Hellman key exchange is a method of securely exchanging cryptographic keys over a public channel and was one of the first public-key protocols as originally conceptualized by Ralph Merkle and named after Whitfield Diffie and Martin Hellman.

1. Bansilal Ramnath Agarwal Charitable Trust's
Vishwakarma Institute of Technology
(An Autonomous Institute affiliated to Savitribai Phule Pune University)
Contributed by,
Saurabh Dhage(17C013) Balaji Channawar(17C017)
Under Guidance of
Prof. Ranjana Jadhav
Masters in Computer Application (Second Year), IT-MCA Department
Presentation on,

2. What is Key
exchange…….?

3. History
Ralph Merkle, Martin Hellman, Whitefield Diffie (1977)
• The Diffie-Hellman key exchange traces its roots
back to the 1970s.
• The two gatherings were working autonomously on
the same issue - Diffie and Hellman on public key
cryptography and Merkle on public key distribution -
when they got to know about one another’s work
and acknowledged there was collaboration in their
methodologies
• Whitfield Diffie and Martin Hellman published their
paper, ’New Directions in Cryptography’. The
collaboration outlined the mechanisms behind a
new system, which would come to be known as
the Diffie-Hellman key exchange.
Diffie-Hellman key exchange

4. What is the Diffie-Hellman key
exchange?
• Diffie–Hellman key exchange is a method of
securely exchanging cryptographic keys
over a public channel
• The Diffie-Hellman key exchange was the
first widely used method of safely
developing and exchanging keys over an
insecure channel.
• As one of the most common methods for
safely distributing keys, the Diffie-Hellman
key exchange is frequently implemented in
security protocols such as TLS, IPsec, SSH,
PGP, and many others.

5. How does the Diffie-
Hellman key exchange
work?
Let’s take a example….

19. Algorithm

20. Step 1: Global Public Elements:
P: Any prime number [1024 to 4096 bits]
Step 3: User A Key Generation
G: Primitive Root of P
Step 2: Select private values for each user
Step 4: User B Key Generation
Step 5: Exchange of user keys from both sides
Step 6: Calculation of secret key by A
Step 7: Calculation of secret key by B
Step 8: The result is same secret key by using their own private keys
Algorithm

21. Advantages of
the Diffie
Hellman
Algorithm
The secret key is never itself
transmitted over the channel
Once the keys are exchanged, the
communication of data can be done
through an insecure channel.
The sharing of the secret key is safe.

22. Cryptanalysis

23. • No Authentication : Algorithm does not provide authentication, which leaves users vulnerable to man-
in-the-middle attacks
• Parameters for number selection: If a real-world implementation of the Diffie-Hellman key exchange
used numbers as small as those in our example, it would make the exchange process trivial for an
attacker to crack. But it’s not just the size of the numbers that matter – the numbers also need to be
sufficiently random.
• Number of multiplications: All of the public information of a Diffie-Hellman key exchange was
intercepted over an open channel including the number of multiplications (n) needed to calculate
(g**b)**a mod p where `a` is Alice's private key and `b` is Bob's private key. This information should be
enough to determine Alice's private key and then decrypt the message.
Cryptanalysis

24. Applications of
Diffie-Hellman
Algorithm
• Diffie Hellman is currently used in many
protocols, namely:
- Secure Sockets Layer(SSL)/Transport Layer
Security (TLS)
- Secure Shell(SSH)
- Internet Protocol Security (IPsec)
- Public Key Infrastructure (PKI)

25. Conclusion
• Due to its advantages, the Diffie Hellman key
Exchange has proved to be a useful key
exchange system.
• While it is really tough for someone snooping
the network to decrypt the data and get the keys,
it is still possible if the numbers generated are
not entirely random or large.
• Also, the key exchange system makes it
possible to do a man in the middle attack, to
avoid it, both parties should be very careful at the
beginning of the exchange.

26. Thank you..