Cryptography Concepts(PGP, Firewall, SSL, HoneyPot, DMZ)

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3 Modes of Firewall
  1. Packet Filtering mode: Firewall has a rule base table in which it keeps things like(Source IP, Destination IP, Source port, destination port, action(DROP, ALLOW)). According to this rule based table, it decides whether it has to allow packets through the network or not. But this has a problem of state of packets. Hence 2nd mode.
  2. Stateful Inspection Mode: In this mode, Firewall keeps track of state of information of packets entering and leaving the network as well. If any packet enters with some state and while leaving it is in another state, then it is a chance of attack.
  3. Application Proxy: This is installed on gateway. In this mode, firewall handles valid requests from external network. Basically it is used to access or deny permissions. For eg, in a web app, the admin has special privileges than any normal user.

Pretty Good Privacy(PGP)

  • Sender’s side-
Sender side
  • Reciever’s Side:
Reciever’s side


HoneyPot is a device that mimics like the original website to attract the attacker. It is used for ethical hacking purposes.


DMZ(Demilitarized Zone)

Case 2
Case 3: Using 2 Firewalls

SSL(Secured Socket Layer)

Replaced by TLS(Transport layer security) today.

Block Diagram



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