Chapter 13: Cryptography and Network Security Question Bank
Cryptography Fundamentals
1. How does the encryption process actually take place?
The text or the written message is encrypted via a special mathematical formula. This formula is specifically known as the "encryption algorithm." Because the ciphertext is now encrypted by this special mathematical algorithm, it would be rendered useless to a third party with malicious intent, because of its totally garbled nature.
2. Are there any other ciphers that are available, other than the Caesar cipher?
Yes, several other ciphers exist including:
- Monoalphabetic Cipher
- Homophonic Substitution Cipher
- Polygram Substitution Cipher
- Polyalphabetic Substitution Cipher
- Playfair Cipher
- Hill Cipher
3. What is a block cipher?
With this method of transposition, the plaintext message is encrypted into its scrambled format by being broken up into blocks and encrypted block-by-block. Here's an example:
Plaintext: I LOVE YOU
Plaintext Block: ILO VEY OUX
Ciphertext Block: OLI YEV XUO
Ciphertext: OLIYEVXUO
Hashing Concepts
4. Explain what is Hash Value?
A Hash Value (also called as Hashes or Checksum) is a string value (of specific length), which is the result of calculation of a Hashing Algorithm. Hash Values have different uses:
- Indexing for Hash Tables
- Determine the Integrity of any Data (which can be a file, folder, email, attachments, downloads etc).
5. Provide a simple example of Hash Function
A one-way function is not just a hash function - a function that loses information - but a function f for which, given an image y, it is difficult to find a pre-image x such that f(x) = y.
A very simple example of a hash function that does not use any advanced math:
if n.even?
0
else
1
end
end
As you can see, it maps a large input space (the natural numbers) into a small output space (the set {0, 1}). And it is one-way: if I tell you that the result is 1, you can't tell me what the input was.
6. Explain MD5.
MD5 is a so-called cryptographic hash function. Although MD5 was initially designed to be used as a cryptographic hash function, it has been found to suffer from extensive vulnerabilities. It can still be used as a checksum to verify data integrity, but only against unintentional corruption.
This basically means that you can give in any bitstring as input for the function, and you will get out a fixed-size bitstring (128-bit in the case of MD5) as output. The output is usually called "digest".
Cryptography Applications
7. What are a couple of significant uses of cryptography in the modern world?
There are heaps of advantages of cryptography in the modern world, and a couple of them are:
- Chip-based payment cards
- Computer and different passwords
- E-commerce
- Defense communications
- Digital Currencies
- Protocol design
- Information authenticity
8. Describe Secret Key Cryptography and Public Key Cryptography? How are they unique to each other?
The two of them are encryption calculations and add to information security.
Secret Key Cryptography can be utilized for both encryption as well as decoding. It is likewise viewed as an symmetric approach and contains just one key.
On the other hand, Public Key cryptography is essentially an asymmetric way to approach. There are two keys in this methodology, and one is essentially the public key (any client can get to the data), and the other key is private (must be gotten to by the director).
9. Brief the central aims of cryptography?
There are 4 prime goals of cryptography:
- Secrecy: Ensuring information is not disclosed to unauthorized parties
- Non-repudiation: Preventing denial of previous commitments or actions
- Authenticity: Verifying the identity of users
- Integrity: Ensuring information has not been altered
10. List the two Signature schemes that are deployed in Cryptography?
- Blind Signature Scheme
- Special Signature scheme
Advanced Cryptographic Concepts
11. In terms of cryptography, explain MAC?
MAC or Message Authentication Code tests the realness or integrity of the message or media access control gadget.
12. Define Salting.
Salting is the process of obfuscating passwords by introducing an arbitrary value to them after they've been hashed.
13. What is the reason behind the use of salting in cryptography?
Since individuals will generally reuse passwords, a hacker with a rundown of normal passwords or taken ones secures his position simpler. A Salt is an arbitrarily created number, yet it decreases the chance of being in a predetermined table.
14. List down the three main types of cryptographic algorithms.
The three main types are:
- Hash functions
- Asymmetric-key algorithms
- Symmetric-key algorithms
15. How Hash Functions are different from Public Key Cryptography and Secret Key Cryptography?
They are basically considered single-way encryption. Unlike Public Key Cryptography and Secret Key Cryptography, they don't have any key in them and their prime function is to make sure that a file has reached its destination without any modification.
16. In case a Cryptography tool is not available and you need to send secret information, would you proceed or wait till the presence of the tool?
It all depends on the security of the network itself in such a case. If the network is secure, the information can be shared. In case not, I will probably wait for the Cryptography tool to be active. This is because any information without proper encryption can easily be leaked.
17. Name the elements of a cryptography tool?
There are basically three important elements:
- The sender which encrypts the information in a secured form
- The receiver where information is received and decoded
- The channel which connects both sender and receiver
Most attacks for data-stealing are made on the channel, which is why data on it always remains in coded form.
18. Explain the concept of Digital Signature Algorithm?
The digital signature algorithm was implemented for the authentication of data in the year 1994. It offers quick signature generation and in addition to this, it ensures better verification of information it is dealing with. It is actually based on computing discrete algorithms and its security actually depends on the size of the key. It can handle key size up to 1024 bits presently.
19. We should not be able to determine the seed from any previous knowledge of the bits sequence. What is this property called?
This is the property of backward unpredictability.
20. What is Forward Unpredictability property?
It is a property when the seed is unknown, and the next output bit in the sequence should be unpredictable.
Network Firewalls
21. What is a Network Firewall?
Network firewall protects your network from unauthorized access. It filters traffic based on the configuration set by the firewall administrator. The firewall basically performs two functions: block and permit traffic based on configuration.
22. How does a firewall work?
Firewall filters network traffic based on the configuration set by the firewall administrator. It can permit or block any port number, web application, and network-layer protocols based on configuration.
23. What can a firewall protect the IT infrastructure inside your organization?
Firewalls are configured to protect IT infrastructure from any unauthorized access. They secure the network by:
- Implementing defined security policies
- Hiding and protecting your internal network addresses
- Reporting threats and activities
- Providing audit logs related to network traffic to the firewall administrator
- Identifying the root cause of a security breach
24. Where does a firewall fit in the security model?
A security model is a scheme for specifying and enforcing security policies. Firewalls secure the network's perimeters by implementing defined security policies, hiding and protecting your internal network addresses, and reporting threats and activities.
25. What is the limitation of the network firewall?
It acts as the first line of defense against any external attack. However, it is weaponless against any internal attack. The firewall acts as a gatekeeper, but inside the house, it can't stop any system harm. A firewall is basically designed to protect the network from other networks.
26. Which type of firewall is more secure, packet filtering firewall or circuit-level gateway and Why?
Circuit Level Gateway is considered more secure because:
Packet-filtering solutions filter traffic based on packet attributes. Circuit Level Gateway filters are based on the communication pattern of TCP/IP packets. Packet-filtering solutions open the system to denial-of-service (DoS) attacks (buffer overflow exploits in "allowed" applications on target machines, connections exhaustion). However, Circuit Level Gateway filters are also not able to protect the system from DoS attacks completely.
27. What is the application Level gateway in the context of a network firewall?
In this case, the firewall acts as a proxy between the internal client and the external server. The main purpose of this type of firewall is to monitor and sanitize external communications. Whenever a user requests something from the Internet, a firewall creates another similar request and checks whether request resources do not have any malware and other security vulnerabilities.
28. What is a Stateful Inspection Firewall?
Stateful inspection is the most effective way to secure a network. It combines the features of the packet filtering firewall, Circuit Level Gateway, and Application Level gateway.
29. What Information Does Stateful Firewall Maintains?
Stateful firewall maintains following information in its State table:
- Source IP address
- Destination IP addresses
- IP protocol like TCP, UDP
- IP protocol information such as TCP/UDP Port Numbers, TCP Sequence Numbers, and TCP Flags
30. What is The Difference between Stateful & Stateless Firewall?
Stateful firewall: A Stateful firewall is aware of the connections that pass through it. It adds and maintains information about users' connections in state table, referred to as a connection table. It then uses this connection table to implement the security policies for users connections. Example of stateful firewall is PIX, ASA, Checkpoint.
Stateless firewall (Packet Filtering): Stateless firewalls on the other hand, does not look at the state of connections but just at the packets themselves. Example of a packet filtering firewall is the Extended Access Control Lists on Cisco IOS Routers.