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CIS3360 > Cryptographic Tools > Flashcards

Cryptographic Tools Flashcards

1
Q

a means to allow two parties, customarily called Alice and Bob, to establish confidential communication over an insecure channel that is subject to eavesdropping.

A

Encryption

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2
Q
  • Also called: single-key encryption
  • Historically, the only type of encryption until public-key methods introduced in late 1970s
  • Still, universally used for providing confidentiality for transmitted or stored data
  • Basic idea: the same key is used by sender and receiver
A

Symmetric Encription

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3
Q
  • plaintext
  • encryption algorithm
  • secret key
  • ciphertext
  • decryption algorithm

These are the components of…

A

Symmetric Encription

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4
Q

even if an opponent knows the algorithm and has the ciphertext, he/she cannot decipher the ciphertext or figure out the key.

A

Strong encryption algorithm

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5
Q
  1. Strong encryption algorithm
  2. Sender and receiver have obtained copies of the same secret key in a
    secure manner

These are the requirements for secure use of …

A

Symmetric Encription

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6
Q
  • Attacker knows the algorithm
  • Attacker has some knowledge of the general characteristics of the plaintext, or even some plaintext-ciphertext pairs
  • Exploits the characteristics of the algorithm to attempt to recover the plaintext or deduce the key that was used
  • If key deduced, effect is catastrophic: all past and future messages encrypted with that key are compromised
A

Cryptanalysis

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7
Q
  • Attacker tries all possible keys on some ciphertext until an intelligible translation into plaintext is obtained
  • On average, half of all possible keys must be tried to achieve success
A

Brute-force attack

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8
Q
  • processes plaintext input in fixed-size blocks
  • a long plaintext message is processed as a series of plaintext blocks
  • for each plaintext block, produces a ciphertext block of the same size
  • most important algorithms: DES, Triple DES, and AES
A

Block cipher

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9
Q

Using the same key to encrypt each block in symmetric block ciphers is known as the ___ mode of operation

A

electronic codebook (ECB)

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10
Q
  • processes the input elements continuously
  • produces output one element at a time
  • uses a key stream generated pseudo-randomly from an input key
  • good for streaming data over a communications channel or browser/Web link
A

Stream cipher

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11
Q

generally runs faster than a block cipher

A

Stream cipher

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12
Q

___ ciphers are better for file transfer, email, databases

A

block

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13
Q

assures confidentiality in data exchange

A

Encryption

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14
Q

___ assures data integrity
• contents have not been altered
• from authentic source
• timely and in correct sequence

A

Message/data authentication

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15
Q

Message/data ___ can be performed either with or without encryption

A

authentication

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16
Q
  • one authentication technique
  • uses a shared secret key and a ___ algorithm
  • ___ is appended to message before transmission
  • ___ is computed separately by recipient and compared with received ___
A

Message authentication code (MAC)

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17
Q

Three most important types of block ciphers

A

DES, Triple DES, and AES

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18
Q

Type of block cypher used to compute MAC

A

DES

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19
Q

MAC

A

Message Authentication Code

20
Q

If received and computed ___ match, the recipient is assured

  1. the message has not been altered
  2. the message came from the alleged sender (since used the shared key K)
  3. if the message includes a sequence number, then sequence assured since attacker couldn’t modify it without affecting the calculation
A

MACs

21
Q
  • Another method for message authentication
  • Uses an algorithm that sender and receiver both know (and maybe attacker, too)
  • Result is a fixed-length code
  • can be encrypted by symmetric or public-key encryption
  • used as a digital signature
A

Hash Function

22
Q
  • can be applied to an entire message or file of any size
  • produces a fixed-length output
  • computationally easy to compute
A

Hash Function

23
Q
  • must be one-way
    • infeasible to find x from H( x ), i.e., to find message given hash value
  • must be collision resistant
    • for a given message, infeasible to find another message that generates the same value
A

Secure Hash Function

24
Q

Used for MACs, digital signatures, and integrity checking

A

Secure Hash Function

25
Q
  • use a different key for decryption than for encryption

* the keys are related mathematically to make this possible

A

Public-Key Encryption

26
Q

Each person has two keys: a ___ that only he/she knows, and a ___ that is broadcast widely; other components are the same as for symmetric systems

A

private key, public key

27
Q

In public-key encryption, the sender encrypts the message using ___

A

the recipient’s public key

28
Q

On receipt, the recipient uses ___ key to decrypt the message.

A

his private

29
Q

Solves key distribution and digital signature issues, but runs much slower than symmetric algorithms.

A

Public-Key Encryption

30
Q
  • uses public-key encryption to compute a shared secret key

* the shared secret key is thereafter used for symmetric data encryption

A

Diffie-Hellman key exchange

31
Q
  • Sender encrypts using his private key
  • Recipients can decrypt using sender’s public key, which they all know
  • Since only sender has the corresponding private key, authenticity is assured
A

Authentication using public-key

32
Q

Encryption (not often), Diffie-Hellman key exchange, Authentication, Digital signature, Key management and distribution are applications of…

A

Public-Key Algorithms

33
Q

Key management and distribution

• used with ___ to assure recipients that alleged public key is genuine

A

certificate authorities (CAs)

34
Q

address the question: How can Alice know that the public key she is using for Bob is really his public key?

A

Digital certificates (DCs)

35
Q

Digital certificates (DCs) are issued by trusted entities called…

A

certificate authorities (CAs)

36
Q

A ___ vouches for an entity (e.g., Bob) and contains Bob’s public key

A

digital certificate

37
Q

The DC is ___ by the CA using its private key; Alice uses the CA’s public key to verify the CA’s signature

A

digitally signed

38
Q

DCs

A

Digital Certificates

39
Q

CAs

A

Certificate Authorities

40
Q
  • Another way to use public-key encryption to protect a symmetric key
  • Does not need for sender and recipient to negotiate a shared secret key
  • Uses a one-time symmetric key
  • Key is encrypted using recipient’s public key and sent to recipient
A

Digital Envelopes

41
Q

Used for:
• generation of keys for public-key algorithms
• generation of stream keys for symmetric stream ciphers
• generation of one-time symmetric keys for use in digital envelopes
• session key generation by key distribution centers or parties to communication
• also used in handshake protocols to prevent replay attacks

A

Random Numbers

42
Q
  • uniform distribution – each value is equally likely

* independence – cannot infer any value from other values

A

Randomness

43
Q

opponent should not be able to predict future element of sequence on basis of earlier elements (similar to statistical independence)

A

Unpredictability

44
Q
  • Cryptographic applications (and programming languages) typically use algorithms to generate “random” numbers
    • algorithms are deterministic
    • therefore, sequences produced are not truly random
A

Pseudorandom Numbers

45
Q

• use algorithms that produce sequences that satisfy statistical randomness
tests (uniformity, independence)
• nevertheless, can be predictable

A

Pseudorandom number generators (PRNGs)

46
Q
  • typically measure unpredictable natural processes
    • e.g., radiation events, gas discharge, leaky capacitors, lava lamps
  • increasingly provided on modern processors
    • e.g., Intel chip that samples thermal noise across undriven resistors
A

True random number generators (TRNGs)

CIS3360 (4 decks)

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