Week 1 Encryption

Encryption:

• Symmetric
  • Old style around forever
  • Simple key copies for the target
  • Same key on both sides
• Asymmetric
  • Public Key Encryption
  • Two Keys
  • Public Key available to anyone
  • Private only owner has

Steps to send encrypted message:

Public & Private keys mathematically made together

1. Message
2. Add message digest (hash)
3. User private key on hash
4. Encrypt using receiver public key (Encrypted)
5. Send
6. Receiver decrypts using private key (Unencrypted)
7. Authenticate using message digest (hash) attached to bottom receiver unlocks using the sender’s public key
   

Certificates & Certificate Authorities:

• TLS
  • 1.3 has no cert in wireshark
    • Because of encryption
  • 1.2 has cert in wireshark
• Cert Contains
  • Issue times
  • Issuer
• Digital Certs provides
  • Confidentiality
  • Authentication
• Remember Certs contain the Publix Key plus other publix information about a server or user
• Certs must have a corresponding Private Key that only the server or user should have
  • Vouching for public keys authority

1. Ca has a private/public key pair
2. Client (alice) has a copy of the Ca public key in trusted CA list
3. Server (bob) has it’s certificate signed by CA’s Private key
4. Client knows that server Certificate is valid by checking the signature with CA Pub Key
   

• How do you know if a cert has been compromised
  • 2 common methods
    • Cert revocation list (CRL)
    • Online certificate status protocol (OCSP)
      • Clients poll a web server