Cryptography and Security

Importance of Cryptography

• Cryptography is a technology used daily, often without users realizing.
• Ensures secure data transmission.
• Security often hinges on the encryption key.

Public Algorithms and Protocols

• Cryptographic protocols and algorithms are public for transparency.
• Aim: Identify vulnerabilities and improve security by discontinuing flawed cryptography.

Focus on Implementation

• Algorithms are generally secure, but implementation can be weak.
• Attackers often exploit poor implementation to access data.

Types of Cryptographic Attacks

Birthday Attack

• Based on the probability principle similar to birthday paradox.
• Involves hash collisions where different plaintexts produce the same hash.
• Example: MD5 algorithm found to have hash collisions.
  • MD5 published in 1992; collisions found in 1996.
  • By 2008, collisions used to forge CA certificates.
• Prevention: Use large hash output sizes to avoid collisions.

Downgrade Attack

• Uses secure algorithms but exploits poor implementation.
• Objective: Force devices to use weaker encryption or none.

SSL Stripping

• A specific type of downgrade attack.
• Involves an on-path attacker sitting between client and server.
• Attacker downgrades secure HTTPS to unsecured HTTP.

SSL Stripping Process

1. Initial Request:

   • User sends HTTP GET request to server.
   • Attacker intercepts, allowing SSL stripping by not redirecting to HTTPS.

2. Proxy Role:

   • Attacker passes initial HTTP request to web server.
   • Server suggests HTTPS, but attacker suppresses this from reaching user.

3. Encrypted Communication:

   • Attacker uses HTTPS with server, has full data access.
   • Attacker sends unencrypted HTTP OK response to user.

4. User Login:

   • User sends credentials over HTTP.
   • Attacker captures and uses credentials to access HTTPS server.

5. Ongoing Communication:

   • Continues between user and attacker in clear text.
   • Attacker maintains encrypted link with server.
   • Allows attacker to view, capture, and modify data.

Summary

• Cryptographic security is crucial and complex.
• Attacks often exploit algorithm weaknesses or implementation flaws.
• Awareness and correct implementation are vital for data protection.