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Networks and Security > 10 - Cryptography > Flashcards

10 - Cryptography Flashcards

1
Q

Authentication

A

Assurane that communicating entity is the one claimed

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2
Q

Access Control

A

prevention of the unauthorised use of resource

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3
Q

Data Confidentiality

A

Protection of data from unauthorised disclosure

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4
Q

Data Integrity

A

Assurance that data received is as sent by an authorised entity

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5
Q

Non-Repudiation

A

Protection against denial by one of the parties in a communication

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6
Q

Availability

A

resource accessible

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7
Q

Problems without Cryptography (4)

A
  • Copy data from disk storage for remote analysis
  • Passively listen on broadcast channels
  • Aggressively monitor traffic through intermediate routers or workstations
  • Actively replay, modify or insert their own messages into the message stream
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8
Q

Solutions to lack of Cryptography (4)

A
  • User encrypt of files
  • DL and NL: in switches and router (VPN)
  • SL: end-to-end data conversion (SSL)
  • AL: in programs such as email agents (PGP)
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9
Q

Ciphertext

A

Encrypted Plaintext

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10
Q

Plaintext

A

Decrypted CipherText

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11
Q

Symmetric Encryption

A

Encryption where the same key is used for encryption and decryption

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12
Q

Asymmetric Cryptography

A

Use of public key cryptography

  • pub key used to encrypt and check signatures
  • private key used to decrypt and sign
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13
Q

Hash

A

A “fingerprint” of a piece of text that will show if it has been altered

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14
Q

Digital Signature

A

A “fingerprint” that is produced with a private key of a pub/priv key pair

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15
Q

Ceaser Cipher Method

A

Each letter in the original message is replaced w/ a letter corresponding to a certain number of letters up/down the alphabet.

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16
Q

Mono alphabetic Substitution

A

uses fixed substitution one the entire message vs poly alphabetic substitution cipher which uses a number of substitutions at different positions in the message

17
Q

One-Time Pad (3)

A
  • Uses one-time pre shared key
  • plaintext is encrypted by combining it w/ corresponding bit or character from the pad using modular add
  • Theoretically unbreakable if pad is generated randomly
18
Q

Types of Symmetric Cryptography

A
  • DES (56 bit)
  • 3DES (168 bit)
  • AES (curent standard)
19
Q

AES

  • keys
  • data operation
  • Key Expansions
  • Rounds
A
  • Keys are 128, 192 or 256 bits
  • Data operation on 4x4 matrix known as “state”
  • KeyExp; round keys are derived from primary key
  • Rounds
  • ->SubBytes: each byte is replaced w/ mother from lookup table
  • ->ShiftRows: last 3 rows of state are shifted a number of steps
  • ->MixColumns: combining of 4 bytes in each column
  • ->AddRoundKey
  • ->Drop MixColumns
20
Q

Key Exchange Method (6)

A

Diffie-Hellman Key Exchange

  • Alice choose prime num g & p, tells Bob
  • Bob picks secret, a, computes g^a mod p, sends result A to Alice
  • Alice picks secret, b, computes g^b mod p, send result B to Bob
  • Bob computes B^a mod p
  • Alice computes A^b mod p
  • Both results are the same, known as the session key used to encrypt private key
21
Q

Public Key Cryptography (3)

A
  • Key Gen: Create pub/priv key pair
  • Encrypt message with pub key
  • Decrypt message with private key
22
Q

RSA Pub/Priv Key Gen

A 
PUB
- prime num p & q
- n=p*q
- z = (p-1)*(q-1)
- k = prime number that is co-prime to z (not divisible by k)
- k, n are pub keys
PRIV
- k*j = 1 (mod z)
- j,n are priv keys
23
Q

Hash Function (2)

A
  • Maps data of arbitrary size to a bit string of a fixed size
  • Designed to operate only one way
24
Q

Properties of Hash Function (5)

A
  • deterministic, same message = same hash
  • fast to compute
  • very difficult to generate a message from its hash
  • small changes result in large changes to hash
  • two different message unlikely to generate same hash
25
Q

Other Hashing functions (2)

A

MAC & Digital Signature

26
Q

Digital Certificate

A

An electronic document that proves ownership of pub key

27
Q

Contents of Dig Cert (3)

A
  • Pub key
  • ID of owner (subject)
  • CA digital signature
28
Q

Format of Dig Cert

A

ISO X.509

- Data encoded using Abstract Syntax Notation (ASN.1)

29
Q

Certificate Path Validation Reason?

A

To verify that certificate path is valid from subject’s certificate up to a trusted root cert issued by a trusted CA

30
Q

Trusting a Certificate (4)

A
  • Root CA such as Google
  • Subjects identified by range of different mean
  • Still possible for rogue SSL cert
  • Certificate Transparency
31
Q

Revoking Certificates Problems (2)

A

CRLs published as soon as a cert is revoked

  • CRLs impose overhead in downloading and processing
  • Subject to DoS attacks
32
Q

Alternative to CRL

A

Online Certificate Status Protocol (OCSP)

Networks and Security (13 decks)

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