Crypto

Question 1

CIA model

Answer 1

C - confidentiality
I - integrity
A - availability

Question 2

Confidentiality

Answer 2

information is only disclosed to those authorized to know it

Question 3

Integrity

Answer 3

Only modify information in allowed ways by authorized parties

Question 4

Availability

Answer 4

Those authorized for access are not prevented from it

Question 5

Threats against CIA model

Answer 5

C - classified information leak
I - fake images/videos
A - Denial-of-Service attacks

Question 6

Cryptographic algorithms goal:

Answer 6

1. Given a key, it should be easy to compute
2. Without the key it should be hard to compute/invert
3. The strength of security is based on the length of a key

Question 7

Window of validity

Answer 7

The minimum time to compromise a cryptographic algorithm

Question 8

Three types of cryptography

Answer 8

1. Cryptographic hash functions - 0 keys
2. Secret-key functions - 1 key
3. Public key functions - 2 keys

Question 9

Cryptographic hash function

Answer 9

Function - h()
Takes a message m and produces a smaller number h(m)

Question 10

Properties of cryptographic hash functions

Answer 10

1. Should be easy to compute h(m)
2. Given h(x) it should be hard to find x
3. Weak + strong collision resistance

Question 11

Weak collision resistance

Answer 11

Given x, it should be difficult to find x’ such that h(x’) == h(x)

Question 12

Strong collision resistance

Answer 12

Give a hash function h(), it should be hard to find two messages x1 and x2 such that h(x1) == h(x2)

Question 13

Private/symmetric key crypto

Answer 13

One key is shared between encryption and decryption, assuming there is a way to keep the secret key in a secure fashion.

Question 14

Public/asymmetric key crypto

Answer 14

Two keys:
Public - can be known to anybody, used to encrypt/verify signatures
Private - should be known only to the owner of the key, used to decrypt messages and sign signatures

Question 15

Secure digest

Answer 15

Often used to verify a downloaded file
A secure digest is a summary of a message, it is a fixed length that characterizes an arbitrary length message
Usually produced by a cryptographic hash function i.e. SHA-256

Question 16

Digital signature

Answer 16

Verifies a message is an unaltered copy

Signer: writes a message m
- computes digest h(m)
- encrypts digest w/ private key enc(h(m)) (signing)
- sends the message and signature <m, enc(h(m)>

Verifier: receives <m, enc(h(m))>
- takes message m and computes digest, h(m) == h’
- decrypts h(m) from message
- verifies h’ == h(m) i.e. the message has not been altered

Question 17

Digital certificate

Answer 17

Idk go read the notes about this one