Netzsicherheit 2: 2 TLS 2.3.5 Schlüsselableitung

Introduction

This tutorial explains the key process of key derivation in TLS 1.2, a crucial component of the Transport Layer Security protocol. Understanding this process is vital for anyone involved in network security, as TLS is the foundational security standard for secure internet communications. By the end of this guide, you will have a clear understanding of how keys are derived in TLS and their significance in maintaining secure connections.

Step 1: Understanding Key Derivation

Key derivation in TLS involves generating session keys from a shared secret and additional data. This process ensures that each session has unique keys, enhancing security.

• Key Components:

  • Pre-Master Secret: A randomly generated secret shared between the client and server.
  • Master Secret: Derived from the pre-master secret.
  • Session Keys: Derived from the master secret.

• Practical Advice: Ensure that the pre-master secret is generated securely and kept confidential.

Step 2: Generating the Master Secret

The master secret is generated using the pre-master secret and additional random data exchanged during the handshake.

1. Input Values:

   • Pre-master secret
   • Client random value
   • Server random value

2. Process:

   • Use a pseudo-random function (PRF) with these inputs to generate the master secret.
   • The PRF combines the inputs to produce a secure and unpredictable output.

• Code Example:

  def generate_master_secret(pre_master_secret, client_random, server_random):
      # Example implementation of PRF for master secret generation
      combined_input = pre_master_secret + client_random + server_random
      master_secret = pseudo_random_function(combined_input)
      return master_secret
  

Step 3: Deriving Session Keys

Once the master secret is established, you can derive session keys for encryption and integrity.

1. Key Types:

   • Client Write Key
   • Server Write Key
   • Client Write MAC Key
   • Server Write MAC Key

2. Derivation Method:

   • Use the PRF again with the master secret and specific labels for each key.
   • Each session key is generated based on a unique label and sequence number to ensure uniqueness.

• Code Example:

  def derive_session_keys(master_secret):
      client_write_key = pseudo_random_function(master_secret + "client write key")
      server_write_key = pseudo_random_function(master_secret + "server write key")
      return client_write_key, server_write_key
  

Step 4: Implementing Key Derivation in Practice

To successfully implement key derivation in TLS, follow these best practices:

• Use Strong Randomness: Always use a secure random number generator for the pre-master secret and random values.
• Regularly Update Keys: Implement key rotation strategies to enhance security over time.
• Understand Security Protocols: Familiarize yourself with the entire TLS handshake process to see how key derivation fits into the bigger picture.

Conclusion

Key derivation is a fundamental process in establishing secure communications using TLS 1.2. By understanding how to generate the master secret and derive session keys, you are better equipped to implement and maintain secure applications. For further learning, consider exploring TLS 1.3, which introduces improvements to the key derivation and overall security mechanisms.