Introduction to Cryptography

Question 1

Which key is used to sign the certificate issued to businesses by a CA?

Answer 1

Private key of the root CA

Question 2

What is a CA?

Answer 2

a trusted third party that signs digital certificates using its private key

Question 3

Which key do businesses send to customers to prove its identity?

Answer 3

Public key of the company

Question 4

What should an administrator use to import and export all items written using X.509 that are part of a chain of trust?

Answer 4

Public Key Cryptography Standard (PKCS) #12

Question 5

What is Public Key Cryptography Standard (PKCS) #12?

Answer 5

PKCS #12 defines an archive file format for storing many cryptography objects as a single file. It is commonly used to bundle a private key with its X.509 certificate or to bundle all the members of a chain of trust.

Question 6

What is Public Key Cryptography Standard (PKCS) #7?

Answer 6

used for generation and verification of digital signatures and certificates managed by a PKI (Public Key Infrastructure). This standard served as the basis for the S/MIME (Secure/Multipurpose Internet Mail Extensions) standard.

Question 7

Is AES symmetric or asymmetric?

Answer 7

symmetric

Question 8

Which two components involved in performing encryption are known to the party that will perform decryption before symmetric encryption is applied?

Answer 8

Cryptographic algorithm

Cryptographic key

Question 9

Employee A created a secret key and wants to send it to Employee B without any coworkers being able to decrypt the message.

Which key needs to encrypt the message?

Answer 9

Employee B’s public key

Question 10

What is ECB and what does it do?

Answer 10

A block cipher mode that encrypts each group with the same key, leaving each group independent of the others.

Question 11

What is a Nonce value?

What can it prevent?

Answer 11

An arbitrary number that can be used just once in a cryptographic communication.
It is often a random or pseudo-random number issued in an authentication protocol to ensure that old communications cannot be reused in replay attacks.
They can also be useful as initialization vectors and in cryptographic hash functions. .

Question 12

What is an Initialization vector used for?

What two block cipher modes have it?

Answer 12

It is a type of salt that adds extra random data to prevent duplicate output for the same input byte.
Used for ECB, and the first block of CBC.

Question 13

What is CTR and what does it do?

Answer 13

A block cipher mode that

Question 14

What is GCM and what does it do?

Answer 14

Incremental symmetric block cipher mode with authentication, has good performance

Question 15

What is a XOR?

Answer 15

exclusive OR; if two input bits are identical, output is 0. If input is different, output is a 1.

Question 16

What is CBC and what does it do?

Answer 16

A block cipher mode that is popular and easy to implement.

Each block is XORed. Very first block uses IV instead of XOR.

Question 17

What is CTR and what does it do?

Answer 17

A block cipher mode that uses an incremental counter (CTR) for randomization, can behave like a stream cipher.
Applies the XOR to the plaintext, and increments a counter for the next block.

Question 18

What is GCM and what does it do?

Answer 18

Block cipher mode that combines CTR mode with Galois authentication.
Very efficient with low overhead, used for packetized data such as wireless, IPsec, SSH, TLS.

Question 19

What two block modes use XOR and how do they do it differently?

Answer 19

CBC XORs by comparing each block to the previous block, very first requires an IV instead.

CTR applies XOR to the plaintext instead and increments the counter for the next block.

Question 20

What two block modes use XOR and how do they do it differently?

Answer 20

CBC XORs by comparing each block to the previous block, very first requires an IV instead.

CTR (and GCM by extension?) applies XOR to the plaintext instead and increments the counter for the next block.

Question 21

What is the only authenticated block cipher mode?

Answer 21

GCM

Question 22

stream cipher is typically not used for what?

Answer 22

stream cipher has low power and CPU overhead, therefore it is not paired with asymmetric encryption which has high overhead.

Question 23

Which mode of block encryption results in the same outcome for matching blocks of a plaintext message?

Answer 23

Electronic Code Book (ECB)

Question 24

Which cipher mode can have blocks of any size?

Answer 24

CTR

Question 25

Uses an initialization vector (IV) to encrypt the first block, then uses the result of the encryption to encrypt the next block

Answer 25

CBC mode

Question 26

Skipjack key/block size

Answer 26

80-bit key and operates on 64-bit data blocks

Question 27

How many transformation rounds does AES use with a 192-bit key?

Answer 27

12

Question 28

How many transformation rounds does AES use with a 128-bit key?

Answer 28

10

Question 29

Which encryption algorithm did the National Institute of Standards and Technology (NIST) designate as a specification for the encryption of electronic information?

Answer 29

IDEA

Question 30

What is the length (in bits) of an MD5 hash output?

Answer 30

128

Question 31

What is the maximum key size for RC4 with WEP?

Answer 31

40 bits

Question 32

Symmetric block encryption is ideal for what?

Answer 32

transferring large amounts of time sensitive data, encrypted storage

Question 33

Symmetric stream is ideal for what?

Answer 33

When speed is a major concern such as video streaming because it uses the same key to encrypt and decrypt large amounts of media.).

Question 34

What is the length (in bits) of the private key used to sign transactions and associated with an individual wallet in the context of Bitcoin?

Answer 34

256 bits

Question 35

Which task does a root CA perform before publishing its own certificate?

Answer 35

Signing it with its private key

Question 36

What is TKIP and its purpose?

Answer 36

It improves WPA over WEP by hashing the initialization vector and secret key

Question 37

Which default port must be open for the IPsec key exchange to be successful?

Answer 37

UDP 500

Question 38

Which protocol field number indicates the virtual private network (VPN) is using Authentication Header (AH)?

Answer 38

51

Question 39

The two main applications of public-key encryption are what?

Answer 39

secret key protection and identity checking.

Question 40

Which combination of cryptographic algorithms is used to create digital signatures based on the U.S. Digital Signature Standards?

Answer 40

SHA-2 and RSA

Question 41

Vigenère cipher uses

Answer 41

polyalphabetic

cipher

Question 42

BIFID cipher

Answer 42

grid that maps scrambled letters into numeric values

and arranging the two-character value (bigram) into two rows.

Question 43

Pigpen is a

Answer 43

mono alphabetic
substitution
four grids created in a square and a diagonal shape.

Question 44

What is an HMAC

Answer 44

HMAC is a message authentication code that can be used to verify the integrity and authentication of the message. It involves hashing the message with a secret key. It is different from standard hashing, which is purely a one-way function.

Question 45

The RSA cracking method involves what?

Answer 45

The RSA cracking method involves using side attacks where the intruder observes the current flows on a processor or the memory utilization of the cache memory storing the private RSA key.

Question 46

a lightweight symmetric encryption method that operates on a 64-bit block using rounds of substitution boxes (S-boxes) and permutation boxes (P-boxes) meant to replace AES

Answer 46

PRESENT

Question 47

Which combination of ciphers and keys is used in bitcoin mining?

Answer 47

Bitcoin uses elliptic curve ciphers (ECC) with a 256-bit private key, and a 512-bit public key.

Question 48

Which encryption method is used in mobile networks?

Answer 48

A5 stream encryption method