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Introduction to Cryptography and Security
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Introduction to Cryptography and Security
Introduction to Cryptography and Security
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1
Question
How is the broad field of cryptology divided into two main branches?
0:25
Answer
Cryptology consists of Cryptography (designing security techniques) and Cryptanalysis (breaking or forging security techniques).
2
Question
What is the primary focus of computer security compared to network security?
0:52
Answer
Computer security protects devices and the data stored on them, while network security protects data during transmission between machines.
3
Question
What are the five main components required for a symmetric encryption system?
1:16
Answer
Plaintext (original message), encryption algorithm, secret key, ciphertext (scrambled message), and decryption algorithm.
4
Question
How does symmetric encryption differ from asymmetric encryption regarding key usage?
1:38
Answer
Symmetric encryption uses one shared secret key for both locking and unlocking. Asymmetric encryption uses two keys: a public key and a private key.
5
Question
What is the difference between the two types of passive attacks: release of message contents and traffic analysis?
2:03
Answer
Release of message contents involves reading private data. Traffic analysis involves studying communication patterns (who, when, how often) to infer secrets.
6
Question
Name and define the four main categories of active attacks.
2:27
Answer
1. Masquerade (pretending to be someone else). 2. Replay (resending old data). 3. Modification (changing message content). 4. Denial of Service (flooding a server).
7
Question
What are the primary security goals threatened by passive attacks versus active attacks?
2:53
Answer
Passive attacks threaten confidentiality. Active attacks threaten integrity and availability.
8
Question
What does Kerckhoffs's Principle state regarding the security of a system?
3:13
Answer
Security should depend solely on the secrecy of the key, not on the secrecy of the encryption algorithm.
9
Question
List and define the five primary security services identified in the X.800 standard.
3:37
Answer
1. Authentication (verifies identity). 2. Access control (limits actions). 3. Confidentiality (secrecy). 4. Integrity (no tampering). 5. Nonrepudiation (legal proof of participation).
10
Question
How do substitution ciphers differ from transposition ciphers?
4:00
Answer
Substitution ciphers replace elements (e.g., A becomes D), changing identity. Transposition ciphers rearrange the order of elements, changing position.
11
Question
What is a Caesar cipher, and why is it considered weak today?
4:21
Answer
It shifts letters by a fixed number of positions. It is weak because it only has 25 possible keys, which can be broken by a brute-force attack.
12
Question
What is the 'fatal flaw' of a Monoalphabetic cipher despite its massive key space?
4:42
Answer
It does not change the relative frequency of letters, making it vulnerable to frequency analysis.
13
Question
How does the Playfair cipher improve upon simple substitution methods?
5:08
Answer
It encrypts pairs of letters (digraphs) using a 5x5 grid, which hides individual letter frequencies.
14
Question
How does the Rail Fence cipher scramble a message?
5:29
Answer
It writes the message in a zigzag pattern across multiple rails and then reads across each rail row.
15
Question
What are the three main areas of security protection based on where the data is?
0:52
Answer
Computer security (on devices), Network security (during transmission), and Internet security (across global networks).
16
Question
What is the main drawback of symmetric encryption despite its speed?
1:38
Answer
It is difficult to distribute the secret key securely to all recipients.
17
Question
What is the defining characteristic of an asymmetric encryption system?
1:38
Answer
It uses a pair of keys: a public key for encryption and a private key for decryption.
18
Question
How does traffic analysis work as a passive attack?
2:03
Answer
The attacker observes metadata like identity, frequency, and length of messages to infer information without reading content.
19
Question
What is the goal of a Denial of Service (DoS) attack?
2:27
Answer
To disrupt a system or server by flooding it with traffic so it cannot serve legitimate users.
20
Question
Why are active attacks generally easier to detect than passive attacks?
2:53
Answer
Active attacks involve changes to data or disruption of services, which leave visible traces or cause errors.
21
Question
According to the X.800 standard, what is the purpose of 'Nonrepudiation'?
3:37
Answer
To provide proof of participation in a communication so neither party can deny their actions later.
22
Question
What is a substitution cipher?
4:00
Answer
A method where each element in the original message is replaced by a different character or symbol.
23
Question
Why is a Caesar cipher with a shift of 3 vulnerable to brute-force attacks?
4:21
Answer
There are only 25 possible shifts in the English alphabet, so an attacker can quickly check every single one.
24
Question
What is frequency analysis and why does it break Monoalphabetic ciphers?
4:42
Answer
It studies how often certain letters appear in a language. Since these ciphers don't change letter frequency, the most common cipher character still represents the most common language character (like 'E').
25
Question
Describe the basic mechanism of the Playfair cipher.
5:08
Answer
It encrypts pairs of letters (digraphs) by placing them in a 5x5 grid and applying specific rules based on their position.
26
Question
What is the Rail Fence cipher?
5:29
Answer
A transposition cipher that writes the plaintext in a zigzag pattern and then concatenates the rows to form ciphertext.
27
Question
What are the two main halves of Cryptology?
0:25
Answer
Cryptography (designing techniques) and Cryptanalysis (breaking/forging techniques).
28
Question
What does Internet security protect specifically?
0:52
Answer
Data as it travels across a global 'network of networks.'
29
Question
What is the role of the secret key in symmetric encryption?
1:16
Answer
It is a shared secret used by both the encryption algorithm to scramble data and the decryption algorithm to unscramble it.
30
Question
Why is asymmetric encryption slower than symmetric encryption?
1:38
Answer
It involves more complex mathematical operations using two different keys (public and private).