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COMPTIA - Sec+ Textbook > Lesson 4: Basic Cryptography Concepts > Flashcards

Lesson 4: Basic Cryptography Concepts Flashcards

1
Q

plaintext (or cleartext)

A

unencrypted message

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2
Q

ciphertext

A

an encrypted message

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3
Q

cipher

A

process (or algorithm) used to encrypt and decrypt a message

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4
Q

cryptanalysis

A

art of breaking or “cracking” cryptographic systems

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5
Q

cryptography

A
  • “secret writing”

- historically, operated using simple substitution or transposition ciphers

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6
Q

security through obscurity

A
  • to keep something secret by hiding it

- attempts to hide details of cipher (secret algorithm)

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7
Q

transport encryption

A

confidentiality means that a message cannot be deciphered without having the appropriate cipher and key (or alternatively the means to crack the cipher)

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8
Q

non-repudiation

A
  • concept that the sender cannot deny sending message

- linked to identification and authentication

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9
Q

T or F. Cryptography can be used to design highly resilient control systems

A

True

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10
Q

control system

A

system with multiple parts, such as sensors, workstations, and servers, and complex operating logic

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11
Q

obfuscation

A
  • art of making a message difficult to understand
  • term used in conjunction with source code used to design computer applications
  • obfuscated source code is rewritten in a way that does not affect the computer compiles or executes code, but makes it difficult for a person reading the code to understand how it works
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12
Q

white box cryptography

A
  • attempts to protect an embedded key while preserving the functionality of the code have all been broken
  • would offer much better Digital Rights Management (DRM) protection for copyright content such as music, video, and books
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13
Q

substitution ciper

A
  • involves replacing units (a letter or blocks of letters) in the plaintext with different ciphertext
  • simple substitution ciphers rotate or scramble letters of the alphabet
  • example:
    ROT13 (an example of Caesarian cipher) rotates each letter 13 places (so A becomes N for instance)
    “Uryyb Jbeyq” means “Hello World”
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14
Q

transposition cipher

A
  • units stay the same in plaintext and ciphertext, but their order is changed
  • example: “HLOOLELWRD”
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15
Q

rail fence cipher

A

if you’re having trouble with the transposition cipher, try arranging groups of letters into columns

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16
Q

key

A
  • most ciphers use a key to increase the security of the encryption process
  • example: if you consider the Caesar cipher ROT13, you should realize that the key is 13
  • key is important, because it means that even if the algorithm or cipher method is known, a message still cannot be decrypted without knowledge of the specific key
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17
Q

T or F. Most modern ciphers are made stronger by being open to review (cryptanalysis) by third-party researchers

A

True

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18
Q

keyspace

A

range of key values available to use with a particular cipher

  • roughly equivalent to two to the power of the size of key
  • some keys within the keyspace may be considered easy to guess (“weak”) and should not be used
  • using a longer keys (2048 bits rather than 1024 bits, for instance) makes the encryption scheme stronger
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19
Q

T or F. Basic substitution and transposition ciphers are vulnerable to cracking by frequency analysis

A

True

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20
Q

frequency analysis

A

depends on the fact that some letters and groups of letters appear more frequently in natural language than others

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21
Q

T or F. A secure cipher must exhibit the properties of confusion and diffusion

A

True

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22
Q

confusion

A
  • key should not be derivable from the ciphertext
  • if one bit in key changes, many bits in ciphertext should change (each plaintext bit should have a 50% chance of flipping)
  • same key should not be used by the algorithm in a predictable way when outputting ciphertexts from different plaintexts
  • achieved by using complex substitutions, employing both whole key parts of the key to output ciphertext blocks
  • confusion prevents attackers from selectively generating encrypted versions of plaintext messages and looking for patterns in their relationship to try to derive the key
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23
Q

diffusion

A
  • means that predictable features of the plaintext should not be evident in the ciphertext
  • if one bit of the plaintext is changed, many bits in the ciphertext should change as a result
  • obtained through transposition
  • prevents attackers from selectively determining parts of the message
  • modern ciphers must use both substitution and diffusion to resist cryptanalysis attacks
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24
Q

trapdoor functions

A

basis of mathematical ciphers is to use an operation that is simple to perform one way (when all the values are known) but difficult to reverse

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25
Q

one-time pad

A
  • an unbreakable encryption mechanism
  • encryption key
  • consists of exactly the same number of characters as the plaintext and must be generated by a truly random algorithm
  • if used properly, one-time pads are unbreakable
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26
Q

XOR

A
  • bitwise operation
  • produces 0 if both values are the same and 1 if the values are different, or, put another way, an XOR operation outputs to truly only if one input is true and the other input is false
  • advantage of XOR compared to an AND or an OR operation is that XOR has a 50% chance of outputting one or zero, whereas AND is more likely to output zero and OR is more likely to output one
  • makes the ciphertext harder to analyze
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27
Q

nonce

A

principal characteristic of a nonce that it is never reused (“number used once”)

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28
Q

initialization vector (IV)

A

random (or pseudo-random)

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29
Q

salt

A

random (or pseudo-random) number or string

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30
Q

weak cipher suites and implementations

A
  • critical vulnerability for an organization

- data that is being stored and processed is not secured

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31
Q

available inputs for cryptanalysis are as follows

A
  • known ciphertext - analyst has obtained the ciphertext but has no additional information about it
  • known plaintext - attacker knows or can guess some of plaintext present in ciphertext, but not its exact location or context
  • chosen plaintext - attacker can submit plaintexts to the same cryptographic process to derive corresponding ciphertexts, facilitating analysis
  • chosen ciphertext -
    attacker can submit ciphertexts to the same cryptographic processes to derive corresponding plaintexts
32
Q

weak key

A
  • one that produces ciphertext that is easy to cryptanalyze
  • examples of weak keys:
  • DES
  • RC4
  • IDEA
  • Blowfish
33
Q

Random Number Generator (RNG)

A
  • module in cryptographic implementation is critical to its strength
  • two principal ways for an RNG to work:
  • true random number generator (TRNG) - sample some sort of physical phenomena, such as atmospheric noise, with a high rate of entropy (lack of order)
  • pseudorandom number generator (PRNG) - uses software routines to simulate randomness
34
Q

side channel attacks

A
  • represents a completely different approach to cryptanalysis
  • monitors timing, power consumption, and electromagnetic emanation
35
Q

resource versus security constraints

A

comparative strength of one cipher over another largely depends on the bit-strength of the key and the quality of the algorithm

36
Q

low power devices

A
  • require more processing cycles and memory space

- slower and means they consume more power

37
Q

low latency uses

A

if cryptography is deployed with a real time-sensitive channel, such as voice or video, the processing overhead on both the transmitter and receiver must be low enough not to impact the quality of the signal

38
Q

data at rest

A

this means that the data is in some sort of persistent storage media

  • examples:
  • financial information stored in databases
  • archived audiovisual media
  • operational policies and other management documents
  • system configuration data
39
Q

data in transit (or data in motion)

A
  • this is the state when data is transmitted over a network
  • examples:
  • website traffic
  • remote access traffic
  • data being synchronized between cloud repositories
40
Q

data in use

A

state when data is present in volatile memory, such as system RAM or CPU registers and cache

41
Q

cryptographic algorithms

A
  • computer security systems:
  • hash functions
  • symmetric encryption
  • asymmetric encryption
42
Q

cryptographic primitive

A
  • single hash function, symmetric cipher, asymmetric cipher
43
Q

crypto module or API (application programming interface)

A
  • algorithms underpinning cryptography must be interpreted and packaged as a computer program (or programming library)
44
Q

cryptographic service provider (CSP)

A
  • makes use of Windows crypto module to perform encryption and/or authentication services
45
Q

hashing algorithms

A

widely used in computer programming to short representation of data

46
Q

checksums

A

ensure validity of data

47
Q

message digest

A

produces fixed length string

48
Q

secure hash algorithm (SHA)

A
  • one of the Federal Information Processing Standards (FIPS)
  • SHA-1
  • this was quickly released to address a flaw in the original SHA algorithm
  • 160-bit digest
  • SHA-2
  • variants using longer digests (notably 256 bits and 512 bits)
49
Q

Message Digest Algorithm (MDA/MD5)

A
  • uses a 128-but hash value

- no longer considered secure for password hashing or signing digital certificates

50
Q

Research and Development in Advanced Communications Technologies in Europe (RACE)

A
  • program set up by European Union
51
Q

message authentication

A
  • prove the integrity and authenticity of a message

- one-way

52
Q

hash-based message authentication code

A

key and message are combined in a way designed to be resistant to “extension” attacks against other means of generating MACs

53
Q

symmetric encryption

A
  • two-way encryption algorithm in which encryption and decryption are both performed by a single secret key
54
Q

symmetric encryption

A

two-way encryption algorithm in which encryption and decryption are both performed by a single secret key

55
Q

stream cipher

A

each byte or bit of data in plaintext is encrypted one at a time

56
Q

rivest ciphers (Ron’s Code)

A
  • family of different encryption technologies designed by Ron Rivest
57
Q

block cipher

A

plaintext is divided into equal-size blocks (usually 64- or 128-bit)

58
Q

data encryption standard cipher

A
  • using 64-bit blocks and 56-bit key
59
Q

advanced encryption standard (AES)

A
  • faster and more secure than 3DES
60
Q

blowfish

A
  • uses 64-bit blocks and variable key sizes

- related cipher Twofish was developed by an extended team to enter AES competition

61
Q

modes of operation

A

refers to way a cryptographic product processes multiple blocks

62
Q

Electronic Code Book (ECB)

A

applies same key to each plaintext block

63
Q

Cipher Block Chaining (CBC)

A

improves ciphertext integrity by applying an Initialization Vector (IV) to the first plaintext block to ensure that the key produces a unique ciphertext from any given plaintext

64
Q

public and private keys in a key pair

A
  • each key is capable of reversing the operation of its pair
  • example:
    if public key is used to encrypt a message, only the paired private key can decrypt the ciphertext produced. the publich key cannot be used to decrypt the ciphertext, even though it was used to encrypt it
65
Q

digital signature

A

prove identity of sender of message and show that message has not been tampered with since sender posted it

66
Q

digital envelop

A

secret key (symmetric) encryption is generally faster than public key cryptography, but public key cryptography can provide higher levels of convenience and security. therefore, often, both are used

67
Q

digital certificates

A

certificate authority (CA) - validate use of public key by issuing subject with a certificate

68
Q

transport encryption

A

refers to encrypting data as it is sent over a network

69
Q

key exchange

A

process by which sender and receiver share key to use for encryption

70
Q

ephemeral key

A

transport encryption often makes use of a different secret key for each session

71
Q

elliptic curve cryptography (ECC)

A

another type of trapdoor function used to generate public/proving

72
Q

Man-in-the-Middle (MitM) attack

A

typically focused on public key cryptography

73
Q

downgrade attack

A

can be used to facilitate a Man-in-the-Middle attack by requesting that the server use a lower specification protocol with weaker ciphers and key lengths

74
Q

replay attack

A

consists of intercepting a key or password hash then reusing it to gain access to a resource, such as the pass-the-hash attack

75
Q

birthday attack

A

type of brute force attack aimed at exploiting collisions in hash functions

COMPTIA - Sec+ Textbook (16 decks)

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