Hashing

Question 1

Easy to compute H(m)

Answer 1

Performance of hash function

Question 2

Given H(m), but not m, it’s computationally infeasible to find m

Answer 2

One-way property of hash function

Question 3

Given H(m), it’s computationally infeasible to find m’ such that H(m’) = H(m)

Answer 3

Pre-image resistance

Question 4

Computationally infeasible to find any pair m1, m2 such that H(m1) = H(m2)

Answer 4

Collision resistance

Question 5

Too long of a hash

Answer 5

Unnecessary overhead

Question 6

Too short of a hash

Answer 6

Birthday paradox

Question 7

Broken, collisions published in August 2004

Answer 7

MD5

Question 8

Too weak for serious applications

Answer 8

MD5

Question 9

Weaknesses were found, but still in use

Answer 9

SHA

Question 10

Collisions in 2^69 hash operations

Answer 10

SHA-1 birthday attack

Question 11

128-bit input digest of four 32-bit words

Answer 11

MD5 input

Question 12

512-bit message block (sixteen 32-bit words)

Answer 12

MD5 input

Question 13

128-bit output (four 32-bit words)

Answer 13

MD5 output

Question 14

Each pass uses a table of constants to update output digest

Answer 14

MD5 operation

Question 15

Developed by NIST, specified in 1993

Answer 15

SHA

Question 16

Input processed in 512 bit blocks, with same padding as MD5

Answer 16

SHA1

Question 17

Input message must be < 2^64

Answer 17

SHA1

Question 18

Message digest output is 160 bits, five 32-bit words

Answer 18

SHA1 output

Question 19

Consists of 80 steps

Answer 19

Block processing in SHA

Question 20

Output of last step is added to input of first step

Answer 20

Block processing in SHA

Question 21

Slower to compute than MD5

Answer 21

Speed of SHA1

Question 22

Only works if set of valid messages is limited by some structure

Answer 22

Authentication via encryption

Question 23

Unsuitable for message authentication

Answer 23

CRC

Question 24

Used to detected random errors, not malicious attacks

Answer 24

CRC

Question 25

Attacker can easily modify message and recompute CRC

Answer 25

CRC can only be used to detect random, not malicious errors

Question 26

Attack where additional information is appended onto hash

Answer 26

Length extension attack

Question 27

Build MAC out of a hash function

Answer 27

Hash MAC (HMAC)

Question 28

S(K,m) = H(k xor opad, H(k xor ipad || m))

Answer 28

HMAC

Question 29

opad and ipad are ____ ciphers

Answer 29

stream

Question 30

pad messages with 0x36 and 0x5c

Answer 30

HMAC processing