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TM112 > Block 3 Part 3 Cryptography > Flashcards

Block 3 Part 3 Cryptography Flashcards

1
Q

Hashing

True or false?
A hashing algorithm produces a unique hash for every different piece of data.

A

False - it should, but it doesn’t always.

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2
Q

Hashing

What do we call the situation whereby a hashing algorithm has produced the same hash for two different pieces of data?

A c___________

A

collision

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3
Q

Collisions

Malicious software has been known to take advantage of collisions by including a fake certificate whose hash c_______ with one from a certificate belonging to a genuine, safe application.

A

collides

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4
Q

Collisions

Are collisions rare or frequent?

A

Extremely rare - but that they exist at all means it is impossible to completely guarantee the integrity of data hashed using MD5

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5
Q

Salting

Salting is a process in which a computer adds a small amount of a_________ d_______ to a password before it is hashed.

A

additional data

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6
Q

Salting

A new salt is generated by a s_______ whenever a new password is created or an existing password is m__________.

A

server
modified

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7
Q

Salting

True or false?
The salt can either be added to the front of a password, the middle, or to the end.

A

False - It can be added to the front or to the
end.

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8
Q

Salting

True or false?
Typically, salting schemes use equal-length salts and hashes.

A

True

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9
Q

Key stretching

The primary goal is to slow down or make it computationally expensive for attackers to guess the original password through b_____-f_____ or d________ a_______.

A

brute-force
dictionary attacks

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10
Q

Encrypting hashes

We can further protect the password file using encryption, obscuring its contents to anyone not possessing a piece of data known as the k___.

A

key

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11
Q

Encrypting hashes

In the most secure systems, passwords are stored, encrypted and decrypted by h________ s________ m________ (HSM) plugged into a USB or Ethernet port on the host computer.

A

hardware security modules

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12
Q

The benefits and limitations of hashing

Put the following statements into the correct categories:

a) Hashing can:

b) Hashing cannot:

confirm data has not been changed since the hash was generated

confirm that data has never been changed

authenticate the creator or sender of data.

obscure passwords from casual inspection.

guarantee the confidentiality of data

A

Hashing can:

confirm data has not been changed since the hash was generated

obscure passwords from casual inspection.

Hashing cannot:

confirm that data has never been changed

guarantee the confidentiality of data

authenticate the creator or sender of data.

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13
Q

Encryption

Encryption is a field of m__________ concerned with o__________ information from unwanted viewers in such a way that the original information can be r_________ later.

A

mathematics
obscuring
recovered

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14
Q

Encryption

Computer encryption algorithms work on b_________ data, so any data that can be represented in binary can be encrypted.

A

binary

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15
Q

Encryption - Some terminology

Plaintext

Plaintext is information that can be directly read by humans or a machine. (For example, this flashcard is an example of plaintext.)

True or false?
The phrase ‘plaintext’ may refer to music, movies and computer programs as well as text.

A

True - Plaintext is an historic term pre-dating computers, when encryption was only used for text. Nowadays, anything can be encrypted, so the phrase ‘plaintext’ may refer to music, movies and computer programs as well as text.

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16
Q

Encryption - Some terminology

Ciphertext

Ciphertext is the e______ d_______.

A

encrypted data

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17
Q

Encryption - Some terminology

A key

A key is a piece of data that determines the v_________ of the ciphertext when plaintext is encrypted (and vice versa).

A

value

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18
Q

Encryption - Some terminology

A cipher

A cipher is the a___________ responsible for turning plaintext into ciphertext, and for restoring ciphertext to plaintext, using one or more keys.

A

algorithm

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19
Q

Encryption - Some terminology

Encryption

Encryption is the process of c_________ p_________ to c____________. (Occasionally you may see it called ‘encipherment’.)

A

converting
plaintext
ciphertext

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20
Q

Encryption - Some terminology

Decryption

Decryption is the process of r__________ ciphertext to plaintext (occasionally ‘decipherment’).

A

reverting

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21
Q

Encryption - Some terminology

The ROT13 cypher

The ROT13 cipher (short for ROTate 13) is
perhaps the simplest form of cryptography possible.

A
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22
Q

Encryption keys

An encryption key is a s______ of b_______.

A

string of bits

23
Q

Encryption keys

The longer the string (the key length), the greater the number of possible keys.

For a key length of n, there are ______
possible keys

A

2^n possible keys
or 2 possible keys

24
Q

Encryption keys

How does the number of possible keys change when we increase the key length by 1?

A

Increasing key length by 1 bit doubles the number of possible keys.

25
Q

The problem with short keys

Short keys are vulnerable to b____-f______ attacks, where one or more computers attempt to decrypt ciphertext by testing every possible key until they produce recognisable plaintext.

A

brute-force

26
Q

The problem with short keys

Testing a million keys per second may sound fast, but this can easily be achieved by a modest PC. Therefore, keys must be sufficiently long that they offer a very large number of possible values. Keys often have lengths of 128, 1024 or 2048 bits, producing unimaginably large numbers of possible key values (see Figure 3.3), rendering brute-force attacks useless.

Encryption that is resistant to brute-force attacks and whose algorithm has no known weaknesses is known as s________ e_________.

A

strong encryption

27
Q

Safeguarding keys

True or false?
The key is the most important piece of information in any practical form of encryption.

A

True

28
Q

Safeguarding keys

We must assume that a malicious party knows which form of e__________ we are using and understands the algorithms used to encrypt and decrypt data.
However, any encrypted messages are safe so long as the value of the k____ is not known to the attackers.

A

encryption
key

29
Q

Symmetric encryption

If the same _______ is used to both encrypt and decrypt a ciphertext, it is know as symmetric encryption.

Does ROT13 use symmetric encryption?

A

Yes, it does.

30
Q

Symmetric encryption

Highly secure symmetric encryption can be performed at very high speeds.
For this reason, most encrypted data sent over networks uses one of a relatively small number of symmetric a__________.

A

algorithms

31
Q

DES

What does DES stand for?

A

The Data Encryption Standard

32
Q

DES

In 1973, the United States National Bureau of Standards proposed a s__________ algorithm to encrypt unclassified data.

A

single

33
Q

DES

What was the name of the algorithm that the NBS chose?

A

Lucifer

34
Q

DES

The NSA mandated reducing the key length of the final Data Encryption Standard from the 64 bits proposed by IBM to ___ bits.

A

56

35
Q

How DES works

DES breaks plaintext into 64-bit blocks, each of which is divided into two halves. One half is scrambled using an algorithm (the F-function) which stretches, mixes and substitutes bits within the 32-bits. The two halves are recombined, then swapped and the process repeated. This is repeated sixteen times to produce the final DES ciphertext. Decryption of DES ciphertext is performed by reversing the process using the same key.

Does DES use symmetric encryption?

A

Yes, it uses the same key for both encryption and decryption.

36
Q

True or false?

DES is no longer used.

A

True - It became too easy to brut-force it.

37
Q

The stopgap between DES and AES was called: T______ D___

A

Triple DES

37
Q

The replacement for DES was: the A_________ E__________ S___________ (AES)

A

Advanced Encryption Standard

37
Q

True or false?
The AES is a symmetric cipher?

A

True

37
Q

AES supports key lengths of _____, 192 or ____ bits

A

128
192
256

(all much longer than DES or even the effective length of 3DES).

38
Q

Amongst other purposes, AES is used to protect data on hard disk p___________, safeguarding Wi-Fi c_________, in password managers and protecting gamers from h_________.

A

partitions
connections
hacking

39
Q

The key distribution problem

Why is having a shared key for encryption and decryption a problem?

A

Because someone might nick it!!!

40
Q

The key distribution problem

The solution to the ‘key distribution problem’ is:

a____________ encryption

A

asymmetric encryption

41
Q

Asymmetric cryptography

In Asymmetric cryptography as uses must create two keys.
What are they?

A

A private key and a public key.

42
Q

Asymmetric cryptography

Alice wants to send a message to Bob, so she asks Bob to send her his public key which she will use to encrypt the message.

  1. Can Bob use his public key to decrypt
    the message?
  2. Can Alice decrypt the message she wrote
    once she has encrypted it with Bob’s
    public key?
  3. If Bob wants to send Alice a private
    what does he need from Alice?
  4. Does Alice have the same private key
    as Bob?
  5. Why must Alice and Bob keep their
    private keys secure?
A
  1. No, only Bob’s private key can decrypt
    the message.
  2. Only Bob’s private key can decrypt
    the message.
  3. He needs her public key so that he can
    use it to encrypt the message.
  4. No, she has her own private key.
  5. Because if someone steals them, they
    can use them to decrypt the messages.
43
Q

Asymmetric key strength

Unlike symmetric keys, which are rarely longer than 256 bits, asymmetric keys are typically very large – usually 1024, 2048 or 4096 bits long.

Do the longer keys mean that asymmetric keys are stronger than symmetric keys?

A

No - it has something to do with the underlying mathematics involved in generating them, we haven’t learnt about this yet.

44
Q

Asymmetric versus symmetric encryption

True or false?
Almost all encryption is performed using symmetric encryption.

A

True

In spite of asymmetric encryption’s ability to avoid the key distribution problem, there are many advantages to using symmetric encryption.

45
Q

Asymmetric versus symmetric encryption

The advantages of symmetric encryption:
a. Symmetric encryption is f____
b. It uses small k_____
c. It is well-suited to encrypting any
amount of d_____

A

a. fast
b. keys
c. data

46
Q

Digital certificates

Genuine keys must be authenticated by a trusted third party.

A digital certificate a_____________ public keys and digital signatures.

A

authenticates

47
Q

Digital certificates

A typical digital certificate consists of many items including,

A version number
A unique serial number…

Can you name another?

A

the name of the organisation that issued the certificate.

First date this certificate is valid.
Last date this certificate is valid.

The certificate holder’s public key.

48
Q

Digital certificates

Most digital certificates are issued by one of a relatively small number of certificate authorities (CAs) who perform the task of authenticating p_______ k____ h_______.

A

public key holders

49
Q

Can we trust the certificate authorities?

In 2017, it was revealed that certificate agencies owned by Symantec had issued a number of digital certificates under questionable circumstances. In order to protect users, G______ took the decision to first downgrade and eventually block Symantec digital certificates in its C________ web browser.

Most certificate authorities realise the reputational damage of being ‘named and shamed’ for improper certificate security and the possible financial damages from affected clients.

A

Google
Chrome

50
Q
A

TM112 (20 decks)

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