2.8 Cryptographic Concepts

Question 1

Define cipher

Answer 1

Algorithm for encrypting/decrypting text, publicly known

Question 2

Define key

Answer 2

Information added to the cipher to encrypt/decrypt data, private since having this allows the encryption/decryption of data

Question 3

5 Steps of Digital Signature (using e-mail as an example)

Answer 3

1. Sender generates a hash of the entire plain text of the message
2. Sender encrypts the hash using his/her private key
3. Recipient receives message in plain text + encrypted hash
4. Recipient decrypts the hash using Sender’s public key
5. Recipient hashes the message and compares it to the hash decrypted from sender

Question 4

How does key length relate to security of encrypted data?

Answer 4

A longer key length produces more secure encryption

Question 5

Define key stretching + 2 libraries/algorithms

Answer 5

1. Making a small encryption key larger by hashing it multiple times
2. Bcrypt, PBKDF2

Question 6

Define hashing (3)

Answer 6

1. Output value generated from algorithm based on input data
2. Irreversible
3. Should produce unique values if provided the same input multiple times

Question 7

What is a hashing collision and what algorithm commonly produces them?

Answer 7

1. When the same output value occurs for different input
2. MD5

Question 8

Define salt

Answer 8

A random value added to input data before hashing

Question 9

2 security benefits of salt

Answer 9

1. Prevents hash collisions
2. Makes brute force attacks, such as Rainbow Tables less effective

Question 10

Define symmetric encryption

Answer 10

A single key is used to encrypt/decrypt data

Question 11

2 challenges with symmetric encryption

Answer 11

1. Securely sharing the key
2. Scalability - hard to share key with many parties

Question 12

Define asymmetric encryption (2)

Answer 12

1. AKA public-key cryptography
2. Uses multiple keys, public and private

Question 13

2 Encryption/Decryption paths with asymmetric encryption

Answer 13

1. Data encrypted with private key can be decrypted by anyone with the public key
2. Data encrypted with public key can only be decrypted whoever has the private key

Question 14

What is difference between private and public keys?

Answer 14

Public key can be shared with anyone, private key must be kept confidential

Question 15

What is the main disadvantage of asymmetric encryption?

Answer 15

Requires more CPU work to generate

Question 16

Define benefit of Diffie-Hellman key exchange and 2 aspects of how it works

Answer 16

1. Allows 2 parties to communicate via symmetric encryption without sharing the key
2. 2 parties use asymmetric encryption to independently generate a single symmetric key
3. Each party combines their private key with other party’s public key which generates the same key for both parties

Question 17

Define Elliptic-Curve Cryptography ECC (3 -what, benefit, and who uses it)

Answer 17

1. Alternate asymmetric encryption algorithm with same security as non-ECC
2. Produces smaller keys and a reduction in size of encrypted data
3. Useful for mobile devices and IoT devices that have less resources

Question 18

Define Perfect Forward Secrecy (PFS) (4)

Answer 18

1. Creates and exchanges a private key that is only valid for a single session
2. Often uses ECC-based algorithm
3. Requires that server and client web-browser is capable of it
4. Prevents future decryption of communication

Question 19

Benefit of quantum computing

Answer 19

Able to process more information using smaller data chunks, i.e. a qubit is both 1 and zero so 4 qubits can represent 16 unique values

Question 20

Benefit of quantum computing to communications

Answer 20

If a qubit communication is monitored, it changes the qubits, allowing detection of this upon receipt, i.e. could detect if an encryption key was intercepted

Question 21

Define steganography

Answer 21

1. Hiding information within an image, audio or video file
2. The file functions as expected, but the information can be extracted with the proper tools

Question 22

Define stream-based cipher

Answer 22

1. Data is encrypted one byte at a time sequentially
2. Mainly used for symmetric encryption
3. IV often added to provide some randomization

Question 23

Define block cipher

Answer 23

Data is divided into blocks, usually 64 or 128-bit, and encrypted

Question 24

Define authenticated encryption

Answer 24

Encryption that simultaneously assures the confidentiality and authenticity of data

Question 25

Define unauthenticated encryption

Answer 25

Only ensures confidentiality, does not ensure authenticity

Question 26

What do counter modes of encryption provide?

Answer 26

Adds an incremented counter value when encrypting the data to create randomization

Question 27

Describe blockchain and public ledgers

Answer 27

Transactions that are tracked via a distributed ledger. Multiple different devices verify a transaction against their copies of a ledger before it is approved to be added to the blockchain. Once approved, it is added to the blockchain with a hash to protect against alteration.