Foundations of Cryptology

Question 1

Decryption?

Answer 1

Restoring plaintext from ciphertext

Question 2

plaintext?

Answer 2

Original, non-coded message

Question 3

Encryption?

Answer 3

Converting plaintext into ciphertext

Question 4

Ciphertext?

Answer 4

Result of encryption

Question 5

Cryptosystem?

Answer 5

System for encrypting and decrypting information

Question 6

Cryptanalysis?

Answer 6

Techniques for deciphering messages without encryption details.

Question 7

Cryptography?

Answer 7

Study of secure communication techniques.

Question 8

Cryptology?

Answer 8

Encompasses both cryptography and cryptanalysis

Question 9

Generic Encryption Notation?

Answer 9

c = Ek(m); m = Dkı(c)

Question 10

Caesar Cipher?

Answer 10

-Overview: Early substitution cipher used by Julius Caesar. mono-alphabetic
-Mechanism: Shifts each letter three places to the left.
-Vulnerability: Susceptible to frequency analysis due to its simplicity.

Question 11

Vigenère Cipher?

Answer 11

-Overview: Polyalphabetic substitution cipher developed by Blaise de Vigenère.
-Mechanism: Uses a repeating keyword to shift letters.
-Strength: Multiple ciphertext letters for each plaintext letter.
-Weakness: Vulnerable to cryptanalysis due to shared frequency distribution a
statistical technique can be applied.

Question 12

One-Time Pads?

Answer 12

Overview: Perfect encryption scheme, invented by Gilbert Vernam.
Mechanism: Uses a pad of random values and the XOR operation.
Requirements: The pad must be used only once, as long as the message, is securely distributed, and truly random.
Practicality: Impractical due to cumbersome key management and distribution.

Question 13

Steganography?

Answer 13

Definition: Hiding data within another media type to conceal its existence.
Methods: Character marking, invisible ink, typewriter correction ribbon, least significant bit alterations in images.
Usage: Information theft, digital watermarks for intellectual property protection.

Question 14

Nonce?

Answer 14

Definition: A random number used once in a cryptographic function.
Purpose: Adds randomness to the encryption process to strengthen it.

Question 15

Initialization Vector (IV)?

Answer 15

Definition: Random values used with algorithms to prevent pattern creation during encryption.
Usage: Ensures identical plaintext values do not produce the same ciphertext when encrypted with the same key.

Question 16

Zero-Knowledge Proof?

Answer 16

Definition: Proving knowledge of a fact to a third party without revealing the fact itself.
Example: Proving knowledge of a password without disclosing it.

Question 17

Split Knowledge?

Answer 17

Definition: Dividing information or privilege among multiple users to prevent any single person from compromising security.
Example: Key escrow, where a secret key is held by a third party until certain conditions are met.

Question 18

Goals of Cryptography?

Answer 18

-Confidentiality: Ensuring that information is not accessible to unauthorized individuals.
-Integrity: Ensuring that information is accurate and complete.
-Authentication: Verifying the identity of individuals and entities.
-Non-repudiation: Preventing individuals from denying their actions.

Question 19

Key

Answer 19

Definition: A piece of information, usually a string of numbers or letters, used in cryptographic algorithms to encode or decode data.
Types: Can vary in size and form based on the cryptographic method.
Security: The strength of encryption depends on the security of the key, influenced by:
The algorithm used.
The size of the key.
How the key is generated.
The key exchange process

Question 20

Three Dimensions of Cryptographic
Systems?

Answer 20

1-the type of operation used for encryption.
2-number of keys used
3-the way the plaintext is processed

Question 21

The Kerckhoff Principle

Answer 21

Principle: The security of a cryptosystem should rely on the secrecy of the key, not the algorithm.

Question 22

Ciphers?

Answer 22

Monoalphabetic Cipher: Substitution cipher using a fixed key.
Polyalphabetic Cipher: Uses multiple substitution alphabets to improve security.
Running Key Cipher: Uses a key based on a book or document.
Concealment Cipher: Hides the message within another message.
Block Cipher
Stream Cipher

Question 23

Types of Operations in Ciphers?

Answer 23

Transposition: Rearranges letters of plaintext.
Substitution: Replaces each character or bit of plaintext with a different character.

Question 24

Other Techniques Used in Ciphers?

Answer 24

Compression: Reduces redundancy before encryption.
Expansion: Increases plaintext size to match key sizes.
Padding: Adds material to the plaintext before encryption.
Key Mixing: Uses subkeys to limit key exposure.

Question 25

Two Attributes of Ciphers?

Answer 25

Confusion: Complicates the relationship between plaintext and key, achieved by substitution.
Diffusion: Spreads changes in plaintext throughout ciphertext, achieved by transposition.