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S&A > Basics > Flashcards

Basics Flashcards

1
Q

Passive setting/attack

A

unauthorised access to data

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2
Q

Active attack

A

unauthorised alteration, deletion, transmission, access prevention

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3
Q

Security services

A

confidentiality
data integrity
data origin authentication
entity authentication
non-repudiation

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4
Q

(C) Confidentiality

A

assurance data cannot be viewed by an unauthorised viewer

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5
Q

(DI) Data integrity

A

assurance that data hasn’t been altered in an unauthorised manner (detection)

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6
Q

(DOA) Data origin authentication

A

assurance that given entity was the original source of data

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7
Q

(EA) Entity authentication

A

assurance that a given entity is involved and currently active in a session
(~identification - who am I communicating with?)

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8
Q

(NR) Non-repudiation

A

assurance that an entity cannot deny its commitment or action (to a third party)

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9
Q

Relationships b/w services

A

DOA > DI (DOA requires DI)
NR > DOA (NR requires DOA)
DOA =/= EA
DOA + Freshness = EA
C =/> DOA

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10
Q

DOA > DI (DOA requires DI)

A

If data was altered, receiver cannot be sure the source is who it claims to be

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11
Q

NR > DOA (NR requires DOA)

A

If the source denies its action, we can challange this claim only if we are sure that the action was performed by the source

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12
Q

DOA =/= EA

A

DOA - emails
EA - systems

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13
Q

DOA + Freshness = EA

A

DOA - certifies the sources is who it claims to be
Freshness - certifies the source is present at the moment of communication

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14
Q

C =/> DOA

A

a hacker can violate DI without breaking encryption

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15
Q

Cryptography

A

design and analysis of mechanisms that provide security services based using mathematical thechniques

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16
Q

Cryptographic primitive

A

cryptographic process that provides a number of specified security services

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17
Q

Cryptographic algorithm

A

specification of a cryptographic primitive

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18
Q

Cryptographic protocol

A

sequence of message exchanges and operations between parties aimed at achieving a security goal

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19
Q

Cryptosystem

A

implementation of primitives and accompanying infrastructure

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20
Q

Plaintext

A

raw data to be transmitted

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21
Q

Ciphertext

A

plaintext after encryption algorithm is applied to it

22
Q

Encryption algorithm

A

set of rules that determines ciphertext for given plaintext and encryption key

23
Q

Decryption algorithm

A

set of rules that determines plaintext for given ciphertext and decryption key

24
Q

Encryption key

A

value put in the e. algorithm to compute ciphertext

25
Q

Decryption key

A

input for a decryption algorithm to compute plaintext from ciphertext

26
Q

Keyspace

A

collection of all possible decryption keys

27
Q

Interceptor

A

(adversary, atttacker)
knows ciphertext and may know decryption algorithm, but does not know the key

28
Q

Mechanisms other than encryption

A
  • steganography
  • access control
  • watermarking
  • honeypots
29
Q

Symmetric cryptosystems

A

Encryption key = Decryption key

30
Q

Public-key cryptosystems (asymmetric)

A

Impossible to determine decryption key from encryption key
Everyone knows encryption key

31
Q

Motivation for public e. algos

A

Negative:
1) device can be “reverse engineered” to extract the algo
2) algo can be leaked
Positive:
1) scrutiny - algos are researched
2) interoperability - easier to adopt to devices and ecosystems
3) transparency - easier to convince a partner the system is secure

32
Q

Kerckhoff principle

A

crypto algorithm shouldn’t required to be a secret

33
Q

Attacker’s knowledge

A
  1. All ciphertexts
  2. Some ptext-ctext pairs:
    - failure to keep decrypted ctexts secret
    - predictable plaintexts (headers)
    - attacker influenced choice of ptext
    - temporary access to encryption/decryption device or interface
    - asymmetric cryptosystem: attacker can generate ctexts using open key
  3. details of encryption algorithm
34
Q

Types of ctext attacks

A

1- ctext only attacks:
=e.algo + ctext
2- known ptext attacks
=some ptext-ctext pairs
3- chosen ptext attacks
=p/ctext pairs corresponding to ptext chosen by the attacker

35
Q

Ways to break e.algos

A

1) determine d.key directly
2) deducing ptext from ctext (not knowing the key)

36
Q

Exhaustive key search

A

= brute-force attack
attempts to decrypt with different d.keys from the key space

37
Q

Ways to find candidate d.keys for exhaustive search (3)

A

1) known c/ptext pairs
2) statistical properties of ptext language
3) contextual info (ex - headers of a receipt)

38
Q

Generic cryptoattacks (3)

A

1- dictionary
2- time memory trade-off
3- side-channel

39
Q

Dictionary attack

A

compiling a dictionary
- fixed key syss: c/ptext pairs dictionary
- syss with derivation of key from pw:
pws/keys dictionary

40
Q

Time memory trade-off attack

A

dictionary + exhaustive search
(optimised exhaustive search)

41
Q

Side-channel attacks (4)

A

attack against implementation of a primitive (not its theoretical design)
- timing attack: different time of computation depending on the value of the key
- power analysis: diff electric power depending on the value of the key
- fault analysis: inputting errors and finding useful info in the response
- padding attacks: manipulate padding process and monitor error messages

42
Q

Features of historical cryptosystems

A
  • symmetric
  • C only
  • based on alphabet
  • outdated
43
Q

Ceasar cipher

A

change each letter by a fixed number of positions in the alphabet

44
Q

Substitution cipher

A

permutation of letters in the alphabet

45
Q

Substitution cipher key space

A

26!

46
Q

Substitution cipher weakness

A

statistical properties of a language (frequency analysis)

47
Q

Ways to improve substitution cipher (3)

A
  • increase the size of alphabet (bigrams, trigrams)
  • allow the same ptext letter to be encrypted with different ctext letters
  • positional dependency
48
Q

Vigener cipher

A

uses keyword for substitution

49
Q

Breaking vigenere cipher

A

1) know length of keyword => break up ctext into groups, apply frequency analysis
2) derive length of kword with statistical properties of the language

50
Q

Ways to improve ciphers (2)

A
  • ptext letter encrypted by number of ctext letters (destroy statistics)
  • positional dependency
51
Q

Destroying statistics of a language (2)

A

1) confusion: each bit of ctext depends on several parts of the key
2) changing one bit of ptext changes half of ctext

S&A (7 decks)

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