deffie hellman algorithm

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Presentation Description

Discovered by Whitfield Diffie and Martin Hellman “New Directions in Cryptography” Diffie-Hellman key agreement protocol Exponential key agreement Allows two users to exchange a secret key Requires no prior secrets Real-time over an untrusted network

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Presentation Transcript

The Diffie-Hellman Algorithm : 

The Diffie-Hellman Algorithm Kaustubh Goswami August 11, 2007

Overview : 

Overview Introduction Implementation Example Applications Conclusion

Introduction : 

Introduction Discovered by Whitfield Diffie and Martin Hellman “New Directions in Cryptography” Diffie-Hellman key agreement protocol Exponential key agreement Allows two users to exchange a secret key Requires no prior secrets Real-time over an untrusted network

Introduction : 

Introduction Security of transmission is critical for many network and Internet applications Requires users to share information in a way that others can’t decipher the flow of information “It is insufficient to protect ourselves with laws; we need to protect ourselves with mathematics.” -Bruce Schneier

Introduction : 

Introduction Based on the difficulty of computing discrete logarithms of large numbers. No known successful attack strategies* Requires two large numbers, one prime (P), and (G), a primitive root of P

Implementation : 

Implementation P and G are both publicly available numbers P is at least 512 bits Users pick private values a and b Compute public values x = ga mod p y = gb mod p Public values x and y are exchanged

Implementation : 

Implementation Copyright, 2001 by NetIP, Inc. and Keith Palmgren, CISSP.

Implementation : 

Implementation Compute shared, private key ka = ya mod p kb = xb mod p Algebraically it can be shown that ka = kb Users now have a symmetric secret key to encrypt

Implementation : 

Implementation Copyright, 2001 by NetIP, Inc. and Keith Palmgren, CISSP.

Example : 

Example Two Internet users, Alice and Bob wish to have a secure conversation. They decide to use the Diffie-Hellman protocol

Example : 

Example Bob and Alice are unable to talk on the untrusted network. Who knows who’s listening?

Example : 

Example Alice and Bob get public numbers P = 23, G = 9 Alice and Bob compute public values X = 94 mod 23 = 6561 mod 23 = 6 Y = 93 mod 23 = 729 mod 23 = 16 Alice and Bob exchange public numbers

Example : 

Example Alice and Bob compute symmetric keys ka = ya mod p = 164 mod 23 = 9 kb = xb mod p = 63 mod 23 = 9 Alice and Bob now can talk securely!

Applications : 

Applications 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)

Conclusion : 

Conclusion Authenticated Diffie-Hellman Key Agreement (1992) Defeats middleperson attack Diffie-Hellman POP Algorithm Enhances IPSec layer Diffie-Hellman continues to play large role in secure protocol creation

Additional Sources : 

Additional Sources http://www.sans.org/rr/encryption/algorithm.php http://www.hack.gr/users/dij/crypto/overview/index.html