Cryptography

Question 1

Plaintext –

Answer 1

the original message

Question 2

Ciphertext –

Answer 2

the encrypted message

Question 3

Cryptographic system –

Answer 3

Specific method of encryption and decryption (also called a cipher or cryptosystem)

Question 4

Transposition –

Answer 4

rearranging elements

Question 5

Substitution –

Answer 5

replacing elements

Question 6

Code –

Answer 6

Words are substituted for other words.

Encryption is NOT the same as a code

Question 7

Block Cipher

Answer 7

Operate on blocks of plaintext and ciphertext – usually 64 bits.

Question 8

Stream Ciphers

Answer 8

Convert plaintext to ciphertext 1 bit at a time.

Question 9

Symmetric –

Answer 9

Same key is used for both encryption and decryption (also called private key encryption)

Question 10

DES

Answer 10

Data Encryption Standard

Question 11

AES -

Answer 11

Advanced Encryption Standard

Question 12

IDEA –

Answer 12

International Data Encryption Algorithm

Question 13

S-Boxes

Answer 13

Integral part of DES algorithm

Selects which 32 bits to use after the key and 32-bit data block have been shifted and combined

Question 14

Skipjack

Answer 14

Uses 80-bit keys
Used in Clipper chip
- Meant to help FBI combat criminals using encryption
- Built in back door for law enforcement
Government has “master key”
- Key escrow – session key held for later release to law enforcement when needed

Question 15

Problems with Symmetric Methods

Answer 15

Same key is used to encrypt and decrypt
Shared key is more likely to be compromised
Possible to brute force short keys
Certain keys are weak
Different keys can produce identical ciphertext
Distribution of keys

Question 16

Diffie-Hellman Method

Answer 16

Each party creates their own private key
Each party computes a public key using a mathematical function of the private key
Public keys are exchanged
Message key is computed from other person’s public key and your own private key
If the math is right, the message key is the same on both sides

Question 17

SET

Answer 17

Secure Electronic Transactions
The SET™ Specification, is an open technical standard for the commerce industry developed by Visa and MasterCard as a way to facilitate secure payment card transactions over the Internet.

Question 18

Digital Certificates

Answer 18

Used to encode and verify messages
Requires a Certificate Authority that creates a digital certificate based on a private key and other authentication information

Question 19

X.509

Answer 19

A popular standard for defining digital certificates

Question 20

VPN

Answer 20

Virtual Private Network

Question 21

Key Escrow and Key Recovery

Answer 21

Keys held in “reserve” in case the original keys are lost or damaged
Usually split between two parties, each with half of the key
Often requires two or more people to access and recover key

Question 22

Differential Cryptanalysis

Answer 22

Look for differences in pairs of messages

Only works on certain ciphers

Question 23

Linear Cryptanalysis

Answer 23

Looks for simple approximation of encryption function

Question 24

Differential Power Analysis

Answer 24

Measures power consumption of hardware encryption devices

Question 25

Covert Channels –

Answer 25

“communication paths that were neither designed nor intended to transfer information at all.”

Question 26

Anonymity –

Answer 26

“finding ways to hide the metacontent of messages (i.e. the sender and the recipients of a message).”

Question 27

Steganography –

Answer 27

concerned with hiding the existence or presence of a message.

Question 28

Watermarks –

Answer 28

used to indicate ownership

Question 29

Unobtrusive communications –

Answer 29

Important on the modern battlefield.

Detection of a signal may lead quickly to the sender being attacked.

Question 30

Tamper proofing –

Answer 30

Information hidden may be a signed “summary” or a hash value which can be used to detect unauthorized modifications.

Question 31

Data augmentation –

Answer 31

Information can be added for the benefit of the public (e.g. details about the work, annotations, purchasing info, …)

Question 32

Substitution systems –

Answer 32

substitute redundant parts of a cover with a secret message.

Question 33

Transform domain techniques –

Answer 33

Embed secret information in a transform space of the signal (e.g., in the frequency domain).

Question 34

Spread spectrum techniques –

Answer 34

adopting ideas from spread spectrum communication

Question 35

Statistical methods –

Answer 35

Encode info by changing several statistical properties of a cover and use hypothesis testing in the extraction process

Question 36

Distortion techniques –

Answer 36

Store information by signal distortion and measure the deviation from the original cover in the decoding step.

Question 37

Cover generation methods –

Answer 37

Encode information in the way a cover for secret communication is created.

Question 38

Stego-only attack:

Answer 38

only the stego-object is available for analysis

Question 39

Known cover attack:

Answer 39

the original cover-object and stego-object are both available.

Question 40

Known message attack:

Answer 40

the hidden message and the stego-object are available.

Question 41

Chosen stego attack:

Answer 41

The stego tool (algorithm) and stego-object are known.

Question 42

Chosen message attack:

Answer 42

goal is to determine the specific stego tool or algorithm

Question 43

Known stego attack:

Answer 43

the tool (algorithm) is known and both the original and steg-objects are available.