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

4 min readMay 24, 2021


Today I’m going to discuss some of the cryptography concepts here.

I will try to explain the concepts in the easiest language as I aim that even a person from non-tech background understands them.

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3 Modes of Firewall

Firewall is basically used to prevent attacks. Firewall does so in 3 modes.

  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

PGP is a 2 level security protocol. Consider the case attacker gets the packet on receiving end,but it will not be able to decrypt the 4914(secret key) itself {as it doesn’t have receiver’s Private key} so it will never be able to decrypt the message being sent.


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


DMZ(Demilitarized Zone)


Consider a case when someone wants to access hosted web server. Then it goes to firewall to take permission, firewall allows. But what if the attacker goes inside the internal network and destroys internal network instead of accessing hosted web server? Hence case 2 arises.

Case 2

So we think of removing the hosted web server outside of our internal network. But in this case, their is a sure short vulnerability of attack from attacker. Hence efficient solution will be case 3.

Case 3: Using 2 Firewalls

So we use 2 firewalls. One specifically to protect our hosted web server and one for the internal network.

SSL(Secured Socket Layer)

Replaced by TLS(Transport layer security) today.

Block Diagram

The server sends its identity Digital certificate(DC) to CA(Certification Authority). CA sends back signed DC. Now whenever the client needs to access the server, it requests it to send it DC. The server responds and gives signed DC to the client. Client sends this DC to CA to verify it the server is authenticated or not. If the response from CA is positive, a virtual tunnel is established and the communication between the client and server can be started now.

These were some of the basic networking protocols I studied in my graduation. Hope the blog was informative.

We’ll meet soon with more such educational blogs. Till then, Be Happy and Make Happy.
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