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Basics Flashcards

(51 cards)

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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

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A

plaintext after encryption algorithm is applied to it

22
Q

Encryption algorithm

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A

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

23
Q

Decryption algorithm

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A

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

24
Q

Encryption key

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A

value put in the e. algorithm to compute ciphertext

25
Decryption key
input for a decryption algorithm to compute plaintext from ciphertext
26
Keyspace
collection of all possible decryption keys
27
Interceptor
(adversary, atttacker) knows ciphertext and may know decryption algorithm, but does not know the key
28
Mechanisms other than encryption
- steganography - access control - watermarking - honeypots
29
Symmetric cryptosystems
Encryption key = Decryption key
30
Public-key cryptosystems (asymmetric)
Impossible to determine decryption key from encryption key Everyone knows encryption key
31
Motivation for public e. algos
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
Kerckhoff principle
crypto algorithm shouldn't required to be a secret
33
Attacker's knowledge
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
Types of ctext attacks
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
Ways to break e.algos
1) determine d.key directly 2) deducing ptext from ctext (not knowing the key)
36
Exhaustive key search
= brute-force attack attempts to decrypt with different d.keys from the key space
37
Ways to find candidate d.keys for exhaustive search (3)
1) known c/ptext pairs 2) statistical properties of ptext language 3) contextual info (ex - headers of a receipt)
38
Generic cryptoattacks (3)
1- dictionary 2- time memory trade-off 3- side-channel
39
Dictionary attack
compiling a dictionary - fixed key syss: c/ptext pairs dictionary - syss with derivation of key from pw: pws/keys dictionary
40
Time memory trade-off attack
dictionary + exhaustive search (optimised exhaustive search)
41
Side-channel attacks (4)
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
Features of historical cryptosystems
- symmetric - C only - based on alphabet - outdated
43
Ceasar cipher
change each letter by a fixed number of positions in the alphabet
44
Substitution cipher
permutation of letters in the alphabet
45
Substitution cipher key space
26!
46
Substitution cipher weakness
statistical properties of a language (frequency analysis)
47
Ways to improve substitution cipher (3)
- increase the size of alphabet (bigrams, trigrams) - allow the same ptext letter to be encrypted with different ctext letters - positional dependency
48
Vigener cipher
uses keyword for substitution
49
Breaking vigenere cipher
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
Ways to improve ciphers (2)
- ptext letter encrypted by number of ctext letters (destroy statistics) - positional dependency
51
Destroying statistics of a language (2)
1) confusion: each bit of ctext depends on several parts of the key 2) changing one bit of ptext changes half of ctext

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