Lesson 9: Implementing Cryptography

Question 1

What is hashing?

Answer 1

Function that converts an arbitrary length string input to a fixed length string output. A cryptographic hash function does this in a way that reduces the chance of collisions, where two different inputs produce the same output

Question 2

List the three attributes that define hashing

Answer 2

The output is of fixed length, meaning the output length depends upon the hashing algorithm used.
The same input to a hashing algorithm will generate the same output every time it is hashed with the same hashing algorithm.
The output of the hashing function cannot be used to recreate the input in any way, which is referred to as being a one-way function.

Question 3

What is a collision in hashing?

Answer 3

A collision occurs when two completely different inputs generate the same hash value.

Question 4

What is another name for a hash algorithm output?

Answer 4

digest
message digest
condensed representation of electronic data

Question 5

List the two most common hashing algorithms

Answer 5

Message Digest Algorithm (MD5)
Secure Hash Algorithm (SHA)

Question 6

How many bits of output does MD5 produce?

Answer 6

128

Question 7

Which hashing algorithm has a high chance of collision?

Answer 7

MD5

Question 8

How many variants of SHA algorithm do we have?

Answer 8

3
SHA-1 generates 160-bit output
SHA-256 generates 256-bit output
SHA-512 generates 512-bit output

Question 9

In what year were attacks against SHA-1 successful?

Answer 9

2005

Question 10

What is HMAC?

Answer 10

HMAC, which stands for hash-based message authentication code, is a method used to verify both the integrity and authenticity of a message by combining a cryptographic hash of the message with a secret key.

Question 11

How does the HMAC process work?

Answer 11

Step 1: The sender uses an HMAC function to produce a MAC by providing the MESSAGE and SECRET KEY to the hash function.

Step 2: The output is a MAC, transmitted with the message.

Step 3: The recipient can compute the MAC by providing the message and secret key as inputs to the same HMAC function the sender uses.

Step 4: If the MAC matches, then the message is intact.

Question 12

What is a cipher?

Answer 12

A cipher is the same as an algorithm.

Question 13

list the 2 categories of symmetric encryption

Answer 13

block cipher and stream cipher

Question 14

What is block cipher?

Answer 14

A type of symmetric encryption that encrypts data one block at a time, often in 128-bit blocks. It is usually more secure, but is also slower, than stream ciphers.

Question 15

What is stream cipher?

Answer 15

A type of symmetric encryption that combines a stream of plaintext bits or bytes with a pseudorandom stream initialized by a secret key.

Question 16

How is the keystream in a stream cipher generated?

Answer 16

Through the use of an initialization Vector (IV)

Question 17

What is IV

Answer 17

A technique used in cryptography to generate random numbers to be used along with a secret key to provide data encryption.

Question 18

List 3 examples of stream ciphers

Answer 18

RC4, Salsa20, ChaCha

Question 19

List 2 examples of block ciphers

Answer 19

3DES, AES

Question 20

What are cipher modes of operations used for?

Answer 20

Modes of operation are used with symmetric block ciphers to enable them to work on large sets of data.

Question 21

List the various modes of operations for symmetric block ciphers

Answer 21

Cipher Block Chaining (CBC)
Electronic Codebook (ECB)
Galois/Counter Mode (GCM)
Counter (CTR)
Output Feedback (OFB)

Question 22

What is asymmetric algorithm?

Answer 22

An asymmetric algorithm is an encryption algorithm that uses the combination of a public and private key to encrypt and decrypt data.

Question 23

This type of encryption proves identity

Answer 23

Asymmetric encryption

Question 23

How are the public and private keys linked in an asymmetric encryption?

Answer 23

The keys are linked in such a way as to make it impossible to derive one from the other.

Question 24

What is asymmetric encryption mostly used for?

Answer 24

For authentication, non-repudiation, and key agreement and exchange.

Question 25

What is the difference between a key exchange and a key agreement?

Answer 25

In a key exchange, the secret or symmetric key is transmitted between parties meanwhile in a key agreement, the secret is mathematically generated by an agreed upon method.

Question 26

List and explain the types asymmetric key agreement methods

Answer 26

Diffie-Hellman (DH) –> It allows for symmetric key exchange using complicated modulus math based upon a common secret.

Elliptic-Curve Diffie-Hellman (ECDH) –> It follows the same process as DH but uses math based on elliptic curves instead of discrete logs.

Question 27

Dh is susceptible to what attack?

Answer 27

logjam attack

Question 28

True or False
Public key cryptography can only be used with very small messages.

Answer 28

True

Question 29

What is a digital signature?

Answer 29

A message digest encrypted using the sender’s private key that is appended to a message to authenticate the sender and prove message integrity.

Question 30

List the methods used in signing a message

Answer 30

Rivest, Shamir, and Adleman (RSA) –> based on factoring large prime numbers. It uses private/public key functions in conjunction with DH.

Digital Signature Algorithm (DSA) –> DSA operates similarly to RSA but is based on logarithmic and modulus math.

Elliptic-Curve Digital Signature Algorithm (ECDSA) –> ECDSA operates similarly to DSA but utilizes properties of elliptic curves in order to provide comparable levels of protection as RSA but with much smaller keys.

Question 31

What is one disadvantage of using DSA over RSA?

Answer 31

Compared to RSA, DSA is faster at generating digital signatures but slower at verifying them.

Question 32

What is a cipher suite?

Answer 32

This is the algorithm supported by both the client and server to perform the different encryption and hashing operations required by the protocol.