2.8 - Cryptographic Concepts

Question 1

What is plaintext in cryptography?

Answer 1

An unencrypted message.

Question 2

What is ciphertext in cryptography?

Answer 2

An encrypted message.

Question 3

What is a cipher in cryptography?

Answer 3

The algorithm used to encrypt and/or decrypt.

Question 4

What is cryptanalysis in cryptography?

Answer 4

The art of cracking encryption.

Question 5

What is a key in cryptography?

Answer 5

What is added to the cipher to encrypt. It is also used to decrypt.

Question 6

What are some ways to help make a weak key stronger?

Answer 6

1) Hashing
2) Key stretching
3) Key strengthening

Question 7

What is key stretching?

Answer 7

Hashing passwords in a key.

Question 8

What is lightweight cryptography?

Answer 8

Cryptography that is focused on devices that have low power and low processing speed. Typically this is IoT devices.

Question 9

What is Homomorphic encryption (HE)?

Answer 9

Encryption that allows data to be worked with while it is encrypted. Calculations and research can be done on the data without actually viewing it.

Question 10

What is symmetric encryption?

Answer 10

Using a single, shared key to encrypt and decrypt the key. If the key gets out, it no longer is effective. It also known as the secret key algorithm.

Question 11

What are some of the pros and cons of symmetric encryption?

Answer 11

Pros
1) Very fast

Cons
1) Doesn’t scale well

Question 12

What is asymmetric encryption?

Answer 12

There are two (or more) mathematically related keys. There is a private key and a public key.

One of the keys is used to encrypt and the other is used to decrypt. Often, the private key is for decryption, and the public key is for encryption.

Question 13

What is the private key in asymmetric encryption?

Answer 13

The key that is kept private. It cannot be derived from the public key.

Question 14

What is the public key in asymmetric encryption?

Answer 14

The key that anyone can see. It cannot be derived from the private key.

Question 15

How can you create a symmetric key from asymmetric keys?

Answer 15

Combining the private key and public key on both sides.

Question 16

What are some pros and cons of asymmetric encryption?

Answer 16

Pros:
1) Scalable
2) More secure

Cons:
1) High power and processing
2) Not as fast

Question 17

What is Elliptic curve cryptography (ECC)?

Answer 17

A key-based technique for encrypting data that generates security between key pairs for public key encryption by using the mathematics of elliptic curves. It uses smaller keys than non-ECC asymmetric encryption and has smaller storage and transmission requirements.

Question 18

What is a hash?

Answer 18

Represents data as a short string of text. It acts as a message digest. Hashing is a one-way trip. It is impossible to recover the original message from the digest.

It is used to store passwords and confidential information.

It can verify a downloaded document is the same as the original and it can act as a digital signature. Different messages will not have the same hash unless there is a collision.

Question 19

What is a collision in hashing?

Answer 19

When a hash is identical to another in a hashing algorithm. No hashing algorithm should create collisions.

Question 20

What is salt is hashing?

Answer 20

Random data added to a password when hashing to make it harder to break the algorithm. Every salt is different. It can’t completely stop reverse engineering.

Question 21

What are digital signatures?

Answer 21

A mathematical algorithm routinely used to validate the authenticity and integrity of a message.

The message is hashed then encrypted. When the hash is decrypted, the receiver takes the message and hashes it with the exact same algorithm to verify that it is the same value.

It is signed with the private key and verified with the public key.

Question 22

What do digital signatures do?

Answer 22

1) Prove the message was not changed (Integrity)
2) Prove the source of the message (Authentication)
3) Make sure the signature isn’t fake (Non-
repudiation)

Question 23

Between asymmetric and symmetric keys, which is often larger?

Answer 23

Symmetric keys are smaller (128-bit or larger)

Asymmetric keys are larger ( often 3,072 bits or more)

Larger keys are harder to brute force

Question 24

What are some considerations when exchanging keys?

Answer 24

Keys need to be secure when sent either in-band or out-of-band. Don’t send them over the net.

If in-band, send them with additional encryption.

Question 25

What is a session key?

Answer 25

A symmetric key that is sent using asymmetric encryptions. The receiver of the key unencrypts the symmetric key, and that becomes the session key.

They are often called ephemeral keys because they are supposed to be temporary.

Question 26

What is Perfect Forward Secrecy (PFS)?

Answer 26

It changes the method of key exchange to make sure that a different set of keys are used every time to prevent the a stolen key from compromising all communications.

PFS requires more computing power. Browser must support PFS.

Question 27

Define Steganography.

Answer 27

Hiding information inside of an image. The security is in the obscurity.

The covertext is the container document or file that contains the message.

Question 28

What are some common forms of steganography?

Answer 28

1) TCP packets
2) Image
3) Invisible Watermarks (yellow dots on printers)
4) Audio files
5) Video files

Question 29

What is a qubit in quantum computing?

Answer 29

The smallest form of information. They are zeros, ones, and any combination in-between, at the same time.

Question 30

What is a stream cipher?

Answer 30

Encryption that is done one bit or byte at a time.

High speed, low hardware complexity
Used with symmetric encryption

Question 31

What is a block cipher?

Answer 31

Encryption that is done in fixed-length groups (often 64-bits or 128-bits). Pad is added to short blocks. Each block is encrypted or decrypted independently.

Used on symmetric

Question 32

What is the mode of operation in block ciphers?

Answer 32

The method of encryption that is used, and it may provide a method of authentication.

ECB (Electronic Codebook)
Each block is encrypted in the exact way

CBC (Cipher Block Chaining)
Adds additional randomization and uses an initialization vector for the first block
Uses XOR

CTR (Counter)
GCM (Galois/ Counter Mode)

Question 33

What is a blockchain?

Answer 33

A system in which a record of transactions is maintained across computers that are linked in a peer-to-peer network.

Question 34

What can cryptography be used for?

Answer 34

Confidentiality
Integrity
Obfuscation
Authentication
Non-repudiation

Question 35

What are some of the limitations of cryptography?

Answer 35

1) Speed: need CPU and CPU needs power
2) Size: encrypting less than the minimum block size
could waste data
3) Weak keys: larger keys are harder to brute force
4) Time: Encryption and hashing takes time
5) Longevity: cryptographic tech becomes less secure
over time
6) Predictability and entropy: hardware random
number generators can be predictable
7) Key reuse: if key is compromised, everything using
that key is at risk
8) Resource vs. security constraints