INFORMATION SECURITY AND AUDIT
1. Overview of information security
2. Information and Network Security Policies
3. Cryptography and PKI
4. Network security applications
5. Design Principles
6. Compliance, Evaluation system and Law
7. Malicious logic and attacks
8. Vulnerability analysis and IT Audit
9. Intrusion detection and log analysis
LAB WORK -ISA
SOLVED PRACTICE QUESTIONS
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Diffie-Hellman Algorithm

The Diffie-Hellman algorithm is a method for securely exchanging cryptographic keys over a public channel. It was one of the first practical implementations of public key exchange and is foundational for many cryptographic protocols.

Features:

  • Asymmetric: Uses two keys, a private key and a public key, for each party involved.
  • Secure Key Exchange: Allows two parties to establish a shared secret key, which can then be used for symmetric encryption.

Working:

  1. Public Parameters: Two numbers are publicly agreed upon: a large prime number p and a base g (also called the generator).
  2. Private Keys: Each party generates a private key. Let's call these a and b.
  3. Public Keys: Each party computes their public key using the formula:
    • Party A: A=g^a mod  p 
    • Party B: B=g^b mod  p 
  4. Exchange Public Keys: The public keys A and B are exchanged over the public channel.
  5. Shared Secret: Each party computes the shared secret key using the other party's public key and their own private key:
    • Party A: s=B^a mod  p
    • Party B: s=A^b mod  p
  6. Result: Both parties now have a common shared secret key sss, which can be used for further encryption.

Security:

  • The security of the Diffie-Hellman algorithm relies on the difficulty of the discrete logarithm problem. Given g, p and g^a mod  p, it is computationally infeasible to determine aaa.

Application:

  • Establishing a shared key for symmetric encryption in secure communications.
  • Used in protocols such as TLS (Transport Layer Security) and IPsec (Internet Protocol Security).

Numerical Example:

  1. Choose p=23and g=5.
  2. Party A selects a private key a=6 and computes the public key A = 5^6  mod 23 = 8.
  3. Party B selects a private key b=15 and computes the public key B = 5^{15} mod 23 = 19.
  4. Party A and Party B exchange their public keys.
  5. Party A computes the shared secret s = 19^6 mod 23 = 2.
  6. Party B computes the shared secret s = 8^{15} mod 23 = 2.
  7. Both parties now have the shared secret s=2.

The Diffie-Hellman algorithm is a fundamental cryptographic protocol that enables secure key exchange, laying the groundwork for secure communication in modern networks.

 

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