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Table of contents
1.
Introduction
2.
Diffie-Hellman Key Problems
3.
Diffie-Hellman Key Predistribution Scheme
4.
Security of Diffie-Hellman Key Predistribution Scheme
5.
Frequently Asked Questions
5.1.
What are the two types of Diffie-Hellman Problems?
5.2.
What is a secret-key cryptosystem?
5.3.
What is hybrid cryptography?
5.4.
What is an Adversarial Goal?
5.5.
What is an Attack Model?
6.
Conclusion
Last Updated: Mar 27, 2024

Diffie-Hellman Key Predistribution

Author RAGHAV ANUSHA
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Introduction

In a key distribution scheme, a trusted authority distributes the information related to the key before everyone is connected to the network. It should be noted that a secure channel is necessary while the keys are distributed. Network users can later use these secret keys to encrypt the messages they wish to transmit over the network.  

Diffie-Hellman Key Pre-distribution

In this article, we will discuss the Diffie-Hellman Key Predistribution and understand it with the help of an example.

Diffie-Hellman Key Problems

There are namely two types of Diffie-Hellman Problems, the decision, and the computational versions. These problems are called Diffie-Hellman Problems because they originate from the Diffie-Hellman Key agreement protocols. The question is if it is possible to track the secret keys if we are aware of the public keys. It is in itself the Diffie-Hellman problem.

Diffie-Hellman Key Pre-distribution Problems
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Diffie-Hellman Key Predistribution Scheme

Diffie-Hellman key Predistribution scheme is a way to establish a shared secret key, it works without the use of any pre-distributed keys. The messages exchanged by two users can be read by anyone but they won’t be able to guess the secret key being used. This predistribution scheme is not responsible for authenticating the participants. However, it is augmented in a few ways to provide authentication. Diffie-Hellman key predistribution scheme is mainly used in Internet Key exchange protocol, which is the central part of the IP security architecture.

Diffie-Hellman Key Predistribution Scheme is an improvised version of the Diffie and Hellman Key agreement scheme. This is a secured computational scheme, given that the Decision Diffie-Hellman problem is intractable. Let us understand this with an example - 

  • Let ‘x’ be a group, and let y be an element belonging to x. Here y is of order n such that the Decision Diffie-Hellman problem is intractable.  
     
  • Every Ninja using the network has a private Long-Lived key (NinjaL) and a public key respectively (NinjaP). Note that NinjaL, which is the Long-Lived key used by Ninja, is more than zero but less than (n-1).
     
  • The public keys of the Ninja using the network are signed by a trusted authority and then certified. 
What is Diffie-Hellman Key Predistribution

Security of Diffie-Hellman Key Predistribution Scheme

Ever wondered what can secure the Diffie-Hellman Key Predistribution scheme from a potential attacker? Well, as we assume the Ninja’s private user key is secured and there is no interaction in the scheme, we don’t expect there to be an active attack. The Diffie-Hellman scheme is secured from attackers only if the Computational Diffie-Hellman Problem is intractable in the subgroup ‘y’. 

The attacker, if in case is able to compute a Diffie-Hellman key, there is a possibility that in polynomial time they are able to retrieve partial information about the key. Henceforth, semantic security of the keys is preferred, meaning that the attacker, in polynomial time, can not retrieve any partial information about the key. The Diffie-Hellman key’s semantic security is seen to be equal to the Decision Diffie-Hellman problem’s intractability. 

Security of Diffie-Hellman Key Pre-distribution

You can read about the difference between Active Attack and Passive Attack in detail here.

Frequently Asked Questions

What are the two types of Diffie-Hellman Problems?

There are namely two types of Diffie-Hellman Problems, the decision, and the computational versions. These problems are called Diffie-Hellman Problems because they originate from the Diffie-Hellman Key agreement protocols.  

What is a secret-key cryptosystem?

It is a cryptosystem in which one secret key is mutually decided between the parties in this system. This private key is used to encrypt and decrypt data.

What is hybrid cryptography?

It is a technique that combines the benefits of both secret and public-key cryptosystems.

What is an Adversarial Goal?

Adversarial Goal is the second aspect of security in cryptography. It tells us what the attacker is attempting to do and the motive behind the attacks. 

What is an Attack Model?

The first aspect of security in cryptography is the Attack Model. It tells us about the information that the attacker can access. 

Conclusion

This article provided an introduction to key distribution and explored the Diffie-Hellman Key Predistribution, the problems, and the security of the Diffie-Hellman Key Predistribution scheme. If you want to dig deeper, here are some related articles - 

Also read - active and passive attacks


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