Chapter 4 and 5: Public Key Cryptography/ Hash functions

Question 1

There are two keys describe the public key and private key to the sender and recipient

Answer 1

sender uses recipients public key to encrypt

Recipient uses private key to decrypt

Question 2

Public key cryptography is based on….

Answer 2

trap door one way function, one way meaning it is easy to compute in one direction but hard in the other direction

Question 3

what is a digital signature

Answer 3

sign by encrypting with your private key, any one can verify the signature by decrypting with public key.but ONLY YOU could have signed it.

Question 4

the general knapsack is …

Answer 4

NP-complete

Question 5

general knapsack is ..

Answer 5

hard to solve

Question 6

super increasing knapsack

Answer 6

is easy to solve, each weight greater than the sum of all previous weights

Question 7

what are the weakness of knapsack

Answer 7

Trap door, one way, lattice reduction

Question 8

Trapdoor with knapsack is

Answer 8

convert SIK into general knapsack using modular arithmetic

Question 9

one way knapsack is

Answer 9

general knapsack easy to encrypt, hard to solve.

Question 10

knapsack is secure or insecure

Answer 10

insecure

Question 11

RSA

Answer 11

2 large prime numbers, N=pq is the modulus.

Question 12

RSA public key is

Answer 12

(N,e)

Question 13

RSA private key is

Answer 13

d

Question 14

what breaks the RSA

Answer 14

factoring the modulus breaks the RSA

Question 15

what is Diffie Hellman (g^a and g^b)

Answer 15

Not used for encrypting or signing

it is based on discrete log problem

Question 16

in diffie hellman what can trudy find to get k

Answer 16

trudy can find a or by then she gets the key k , if trudy can solve discrete log problem she can find a or b

Question 17

what must you be aware of in MIM

Answer 17

Man in the middle, attack on diffie hellman

Question 18

digital signature provides what

Answer 18

provides integrity and on repudiation

Question 19

No non-repudiation with ..

Answer 19

Symmetric keys

Question 20

what does the certificate contain

Answer 20

it contains the name of the user and users public key and other info. it is signed by the issuer a CA certificate authority

Question 21

the signature on a certificate is verified using what

Answer 21

CA’s public key.

Question 22

what is PKI

Answer 22

Public key infrastructure: the stuff needed to securely use public key crypto

Question 23

what are the three PKI trust models

Answer 23

Monopoly model, oligarchy model, anarchy model

Question 24

what are the plus’s in symmetric key

Answer 24

sped, no public key infrastructure (PKI) needed

Question 25

what are the plus's in public key

Answer 25

signatures (non-repudiation) | no shared secret (but, private keys...)

Question 26

what are the 5 things a crypto hash function must have?

Answer 26

``` Compression- output length is small efficiencry- easy to compute for any x one-way wak collision resistance strong collision resistance ```

Question 27

what are the popular crypto hashes

Answer 27

MD5 and SHA-1

Question 28

what is MD5

Answer 28

128 bit output MD5 collisions are easy to find invented by Rivest

Question 29

what is SHA-1

Answer 29

160 but output | a U.S government standard inner workings similar to MD5

Question 30

what is HMAC

Answer 30

a hashed MAC

Question 31

where are hash's used

Answer 31

``` authentication message integrity message fingerprint data corruption detection digital signature efficiency ```

Question 32

Spam reduction work for the sender is

Answer 32

2 to the N hashes

Question 33

spam reduction work for the recipient is

Answer 33

always 1 hash

Question 34

spam reduction chose n that is

Answer 34

work acceptable for normal email user | work is too high for spammers

Question 35

where do we use random numbers

Answer 35

generate keys symmetric keys RSA: prime numbers Diffie Hellman: secret values

Question 36

what is entropy

Answer 36

is a measure of randomness

Question 37

where are random numbers being used to gnerate keys

Answer 37

Symmetric keys RSA: prime numbers Diffie Hellman: Secret values

Question 38

cards that are shuffled what factor

Answer 38

52! > 2^225 possible shuffles

Question 39

Randomness two features

Answer 39

can get quality random bits by such methods | BUT quantity of bits is very limited

Question 40

what is watermark's two features

Answer 40

visibility and robustness

Question 41

describe visibility in water mark

Answer 41

Invisible- watermark is not obvious | visible such as TOP SECRET

Question 42

what are the two features in robustness

Answer 42

robust and fragile

Question 43

describe robust

Answer 43

robust is readable even if attacked example add robust invisible mark to digital music, if pirated music appears on internet can trace back to original soure of leak

Question 44

describe fragile

Answer 44

fragile is damaged if attacked example add fragile invisible mark to audio file, if watermark is unreadable, recipient knows that audio has been tampered integrity