Internet Security

• What is a firewall?

  Hardware or software that controls access to and from a network
• What is done during packet filtering?

  Packets of data is inspected by the firewall to check which port it is attempting to use
• What happens if a packet is allowed through a packet filter?

  The port is opened for the duration of the connection, otherwise it is automatically rejected
• What is the problem with packet filtering?

  Malware packets could be disguised as packets that are allowed through whitelisted ports
• What happens during stateful inspection?

  The payload of a packet is examined before allowing access into a network
• What is the function of proxy servers?

  They make web requests on behalf of your own computer, hiding the request IP address from the recipient
• What is the function of a proxy server?

  • Enables anonymous surfing
  • Can be used to filter online content
  • Logs user data with their requests
  • Provides cache of a commonly used website
• What is encryption?

  Encoding a plaintext message so that it cannot be deciphered unless you have a key to decrypt it
• What is the problem with symmetric encryption?

  It is vulnerable to man in the middle attacks
• What is a man in the middle attack?

  Where a third-party intercepts a key and uses it to decrypt a file that wasn't intended for them
• An advantage of symmetric encryption is that it is relatively fast
• Asymmetric encryption is used for email. The process is:

  • Recipients public key used to encrypt data
  • Data sent
  • Data received by recipient is decrypted with recipient's private key
• What is hybrid encryption?

  The beginning of the session uses asymmetric encryption to share a private key for symmetric encryption. This is faster than asymmetric encyption
• How is a digital signature created?

  Irreversibly reducing the unencrypted message to produce a hash, which is then encrypted with the sender's private key
• What is the process of creating a digital signature?

  • Hash is calculated from file
  • Hash encrypted with sender's private key
  • Digital signature created
  • Digital signature attached to file
  • File encrypted with receivers public key
  • File sent
  • File decrypted with receiver's private key
  • Digital signature decrypted with sender's public key
  • Hash value recalculated and compared to ensure file is valid
• What is a digital certificate, and when is it created?

  When a sender digitally signs a message, they also send their digital certificate.

  A trusted known as a Certificate Authority (CA) provides a digital certificate which includes:

  • A serial number
  • name of the CA
  • expiry date
  • name of holder
  • holder's public key
  • CA's digital signature used to verify validity of certificate
• What are digital certificates used for?

  Verifying the identity of the owner of each public key