Encryption

Question 1

Explain Cipher Disk

Answer 1

Use two disks with letters, can be polyalphabetic or monoalphabetic.

Question 2

Explain Blowfish

Answer 2

Symmetric block cipher
32 to 448-bit keys
64-bit blocks

Question 3

Explain OFB

Answer 3

Output Feedback
Uses previous ciphertext for feedback as the subkey that is XORed with plaintext
Error in the beginning do not continue throughout the encryption process

Question 4

Explain IDEA

Answer 4

International Data Encryption Algorithm
Symmetric block Cipher, designed to replace DES
128-bit key, 64-bit block
patented

Question 5

Explain El Gamal

Answer 5

Asymmetric using Discrete Logarithm, like Diffie-Hellman

Question 6

Explain Running-Key Cipher

Answer 6

adds letters of a text to letters of the message to get the cipher text. If the result is more than 26, uses modular math.

Question 7

Explain One-Time Pad

Answer 7

Unbreakable, share secret pad, don’t reuse.

Question 8

Explain ECB

Answer 8

Electronic Code Book, weakest form of DES.

No initialization vector or chaining.

Question 9

Explain CTR

Answer 9

Counter mode
Uses a counter
Can be done in parallel

Question 10

Explain Vigenere Cipher

Answer 10

Polyalphabetic, French, 16th Century.
Vigenere Square formed by 26 letters across the top, and down the left axis.
Random key is repeated, using the letter of the key with the letter of the plain text to find the cipher letter in the middle of the matrix

Question 11

Explain Enigma, SIGABA, and Purple

Answer 11

Enigma was used by Germany in WW2
SIGABA was used by the US in WW2
Purple was used by Japan in WW2

Question 12

Explain CBC

Answer 12

Cipher Block Chaining
block mode using XOR
uses initialization vector and chaining

Question 13

Explain RSA

Answer 13

Asymmetric using Prime Number Factoring

Public and Private keys

Question 14

Explain Wassenaar Arrangement

Answer 14

Restricted export of encryption technology to Terrorist countries.

Question 15

Explain RC6

Answer 15

Symmetric block cipher
128, 196, 256-bit keys
128-bit block

Question 16

Explain COCOM

Answer 16

Restricted export of encryption technology to from COCOM members (US and allies), to non-COCOM members (Russia and others during the cold war), was restricted

Question 17

Explain RC5

Answer 17

Symmetric block cipher
0 to 2040-bit keys
64 or 128-bit blocks

Question 18

Explain the Ceaser Cipher

Answer 18

Monoalphabetic rotation cipher-shifting letters.
The amount shifted is the key.
Susceptible to frequency analysis.

Question 19

Explain Single DES

Answer 19

64-bit blocks with 56-bit key, using 16 rounds

Question 20

Explain CFB

Answer 20

Cipher Feedback

stream mode, uses initialization vector and feedback

Question 21

What are the five modes of DES

Answer 21

Electronic Code Book (ECB)
Cipher Block Chaining (CBC)
Cipher Feedback (CFB)
Output Feedback (OFB)
Counter Mode (CTR)

Question 22

Explain Diffie-Hellman

Answer 22

Asymmetric using Discrete Logarithm

Key exchange Protocol

Question 23

Explain ECC

Answer 23

Elliptic Curve Cryptography
Asymmetric using discrete logarithm as applied to elliptic curves.
Strongest asymmetric encryption
used in low power devices.

Question 24

Explain Triple DES

Answer 24

Applies Single DES three times per block
Uses encrypt/decrypt/encrypt
Uses 1, 2 or 3 keys

Question 25

Explain AES

Answer 25

Advanced Encryption Standard
Symmetric block cipher,
128-bit key with 10 rounds
192-bit key with 12 rounds
256-bit key with 14 rounds
128-bit block
Uses four functions: SubBytes, ShiftRows, MixColumns, and AddRoundKey
Formally known as Rijndeal

Question 26

Explain Scytale

Answer 26

Sparta, Rod

Used by Sparta by using a rod.

Question 27

Explain Twofish

Answer 27

Symmetric block cipher
128-256-bit keys
128-bit block