Chapter Seven & Eight

Question 1

Cryptography

Answer 1

The study of securing information through the use of codes, ciphers, encryption, and other security techniques

Question 2

Cryptanalysis

Answer 2

The study of how ciphers, codes, and cryptosystems work
and why

Question 3

Cryptology

Answer 3

The combined study of cryptography and cryptanalysis

Question 4

Kerckoff’s Principle

Answer 4

he security of a cryptosystem should not rely on the secrecy of the system

We want to assume attackers have access to knowledge before deploying
attacks

Question 5

Caesar Cipher

Answer 5

– Replace each letter in a text by the 3rd letter
following it in the alphabet:
– ABCD becomes DEFG; CAT becomes FDW
– Variations rotate by different amounts
– Monoalphabetic substitution cipher

Question 6

Vigenere Cipher

Answer 6

– Named after 16th century author Blaise
Vigenère
– Uses a series of different rotations
– The “key” may be a word – each letter
indicates a rotation
– Polyalphabetic substitution cipher

Question 7

he Data Encryption Standard (DES) (1977)

Answer 7

– Developed by IBM and US government
– Adopted by banks to protect the earliest
electronic bank transactions
* Supported 56-bit keys: 256 different keys
– 72,057,594,037,927,900
* Over 72 quadrillion keys (7 x 1016)

Question 8

• AES

Answer 8

128-bit, 192-bit, and 256-bit keys
– Smallest key is still too large for DES Cracker
* 128-bit key would take 1019 years

Question 9

Key stream…

Answer 9

It is a stream of bits with these properties:
– Attackers can’t predict its contents in practice

Question 10

The RC4 Stream Cipher (1987)

Answer 10

Rivest Cipher 4 (RSA)
* Prioritized speed of encryption without loss of
data in limited systems
* Byte cipher, doesn’t work at the bit-level
* Used in Microsoft End-to-End Encryption, PDF,
SSL, etc.
* Broken due to biases in the secret key

Question 11

Pseudo-Random Numbers And Key
Streams (PRGNs)

Answer 11

Statistically random numbers: good for
simulations, bad for cryptography

Question 12

Known Ciphertext

Answer 12

or ciphertext only
– All we know is the ciphertext
– Most difficult situation, most common

Question 13

Known Plaintext

Answer 13

– We know some plaintext to match some of the ciphertext encrypted with a particular key

Question 14

Chosen Plaintext

Answer 14

We can choose some plaintext to encipher
with our victim’s cipher, and retrieve the
ciphertext

Question 15

Computational foundations

Answer 15

All strong encryption algorithms are built on top of “mathematically
intractable” algorithms (prime factorization – finding the factors of
extremely large prime numbers, discrete logarithms, etc.)

Question 16

Cryptonet

Answer 16

set of people or devices that all
share the same secret key – transitive trust

Question 17

Public and private keys…

Answer 17

– Public keys can be shared with attackers
– Private keys are kept secret by the owner

Question 18

Elliptic Curve Cryptography

Answer 18

Similar to Diffie-Hellman
– Can calculate a shared secret
– Uses elliptic curve computations:
(y2 = x2 + ax + b)(mod p)
Elliptic curve key is 2–3x larger than a secret
key yielding a comparable search space

Question 19

Quantum key distribution

Answer 19

-Applies Heisenberg’s Uncertainty Principle to detect eavesdropping
– Demonstrated using satellite communications

Question 20

Quantum cryptanalysis

Answer 20

– Schor’s algorithm factors very large numbers
– A large quantum computer could attack
current public-key crypto techniques

Question 21

Birthday attack:

Answer 21

comes from the birthday
paradox, where in
n group of people, two of
which are bound to have the same birthday

Randomly create two of the same file until the
same hash value is generated

Question 22

MAC

Answer 22

cryptographic checksum applied to a
message

Question 23

Keyed hash

Answer 23

– A way of verifying that some of our data has
not been modified by an attacker
– Keyed Hash – a value created from both the
message and the secret key to create a MAC
(Message Authentication Code)

Question 24

Digital signature

Answer 24

A hash of the message
encrypted with the private key of the sender
– Includes…
* Hashing algorithm used
* Contents of the message
* Key generation algorithm
* Any other information provided by a CA

Question 25

Man-In-The-Middle Attack (MITM)

Answer 25

attack
where any communication of the keys is
intercepted and spoofed by the attacker
– Forge messages from one party as legitimate
without knowing the keys themselves; simply
use them to create false messages

Question 26

What is bit-flipping

Answer 26

It refers to a type of attack where an attacker modifies individual bits within a block of encrypted data in order to change its meaning or functionality. This attack is particularly effective against encryption schemes that use stream ciphers or block ciphers in certain modes of operation.

Question 27

Volume

Answer 27

a logical space containing its own filesystem

Question 28

a logical space containing its own filesystem

Answer 28

 Designed using loops or rounds
 Implements key schedules for different keys
 Feistel structure (AKA Feistel network)
 Skeleton of most block ciphers
 Drawbacks of block ciphers

Can’t account for information outside of where information is
encrypted

Question 29

Social engineering

Answer 29

Deceptive or manipulative practices to gain information from someone
(passwords, system configuration information, etc.)

Question 30

RC4 was used in early wireless encryption (T/F)

Answer 30

True

Question 31

Mode

Answer 31

is a technique for applying the cipher by
mixing its outputs to hide ciphertext patterns

Question 32

Cipher stream modes: (T/F) Both OFB and CTR can generate the keystream
before the data is available to encrypt

Answer 32

True

Question 33

Mode uses both XOR and the block cipher to
construct the ciphertext stream (T/F)

Answer 33

True

Question 35

Most modes are mixing modes that hide patterns… Typical modes?

Answer 35

Typical modes:
– Electronic codebook (ECB) – no mixing at all
– Output feedback (OFB) – creates a keystream
– Counter (CTR) – creates a keystream
– Cipher feedback (CFB) – blocks and streams
– Cipher block chaining (CBC) – block oriented

Question 36

Drawbacks of block ciphers

Answer 36

Can’t account for information outside of where information is
encrypted

Question 37

AESGCM, XTS modes

Answer 37

Modern solution incorporating intermediate authentication values
(tag), advanced counter mode operations

Question 38

AES GCM ( Advanced Encryption Standard in Galois Counter Mode)

Answer 38

Requires the use of a “tag” to authenticate
certain vulnerable features about the
message
* Length of message, patterns in
message/ciphertext/encryption algorithm
vulnerabilities, etc

Question 39

AEAD –

Answer 39

Authenticated Encryption with
Additional Data

Question 40

MS Windows – BitLocker feature

Answer 40

True

Question 41

Apple OS X – FileVault feature

Answer 41

True

Question 42

PGPDisk – part of commercial PGP crypto

Answer 42

True

Question 43

Veracrypt – open-source FDE package

Answer 43

True

Question 44

XTS is length-preserving

Answer 44

Does not incorporate padding or
concatenation or reduction of encrypted data