3 - 2: Symmetric Cryptography

Question 1

Data Encryption Standard (DES) history

Answer 1

An IBM standard created in the 1970s to standardize government agency algorithms using the Feistel function

Question 2

Data Encryption Standard (DES) key facts

Answer 2

Symmetric algorithm, block cipher of 64-bit blocks, 56 bit key, now considered insecure

Question 3

3DES

Answer 3

A workaround where DES is applied 3 times with 3 keys. 3 different keys is most secure.

Question 4

Why 3DES and not 2?

Answer 4

Vulnerable to a meet-in-the-middle attack

Question 5

Advanced Encryption Standard (AES)

Answer 5

Symmetric algorithm, block cipher of 128-bits, key lengths of 128, 192, or 256 bits, uses both substitution and transposition

Question 6

Blowfish

Answer 6

Public domain algorithm, symmetric, block cipher of 64 bits, key between 32 and 448 bits, no longer secure

Question 7

Twofish

Answer 7

Public domain encryption using Feistel network, symmetric, 128-bit blocks, keys of 128, 192, or 256 bits, still secure

Question 8

RC4

Answer 8

A symmetric stream cipher widely used to encrypt network traffic, enabling WAP, WEP, SSL, and TLS.

Question 9

RC4 keystream

Answer 9

The stream is pseudorandom: while the stream is random, it is initialized with a selected encryption key

Question 10

RC4 key facts

Answer 10

Symmetric, stream cipher, variable length between 40 and 2048 bits, no longer considered secure

Question 11

Cipher mode

Answer 11

Describes how an algorithm encrypts and decrypts data

Question 12

Electronic codebook (ECB)

Answer 12

Context: you’ve encrypted plaintext with independent, individual block ciphers. The ECB is a library of sorts containing the keys and ciphertext.

Simulates a digital codebook providing an encrypted version of each possible input. Encrypting the same block with the same key results in identical ciphertext blocks

Question 13

Cipherblock chaining (CBC)

Answer 13

Requires previous blocks to be encrypted, feeding previous blocks into the next block’s encryption using exclusive or logic

Question 14

Counter mode (CTR)

Answer 14

Uses a random value and a counter (beginning at 0), which are added and included in the encryption block, then proceeds using exclusive or logic. Allows a block cipher to behave more like a stream cipher.

Question 15

Glaois/Counter mode (GCM)

Answer 15

Adds authentication to counter mode

Question 16

Steganography

Answer 16

Hiding information within another file