Chapter 2 Flashcards
Universal technique for providing confidentiality for transmitted/stored data
Symmetric Encryption
Need strong encryption algorithm
Sender and receiver must have obtained copies of the secret key
2 requirements for Symmetric Encryption
Cryptanalytic attacks
Brute-Force attack
Attacking Symmetric Encryption
Rely on nature of algorithm
Knowledge of general characteristics of plain text
Cryptanalytic attacks
Try all possible keys on ciphertext until plaintext is obtained
Brute-force attack
Most widely used encryption scheme
Uses 64 bit plaintext block and 56 bit key to produce 64 bit ciphertext block
Data Encryption Standard (DES )
Repeats DES algorithm 3 times using 2 or 3 unique keys
Pros: 168 bit key length overcomes vulnerability to brute-force
Cons: algorithm is sluggish in software
64 bit block size
Triple DES (3DES)
Replaced 3DES
Symmetric block cipher
Improved efficiency
Advanced Encryption Standard (AES)
Typical symmetric encryption is applied to a unit of data larger than a single 64 bit or 128 bit block
Practical Security Issues
Simplest approach to multiple-block encryption
Electronic codebook (ECB) mode
Processes the input one block of elements at a time
can reuse keys
More common
Block Cipher
Processes the input elements continuously
Produces output one element at a time
Encrypts plaintext one byte at a time
Stream Cipher
Protects against active attacks
Verifies received message is authentic
Can use conventional encryption
Message Authentication
Can be applied to block of data of any size
Produces a fixed-length output
One-way or pre-image resistant
Hash function requirements
Cryptoanalysis - exploit logical weaknesses in the algorithm
Brute-force attack - strength of hash function depends solely on the length of the hash code
2 approaches to attacking a secure hash function
SHA most widely used algorithm
Security of Hash functions
Passwords
Intrusion detection
Additional Secure hash functions
Based on mathematical functions
Asymmetric - uses 2 separate keys
Public-key Encryption Structure
Computationally easy:
- to create key pairs
- for sender knowing public key to encrypt messages
- for receiver knowing private key to decrypt ciphertext
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Requirements for public-key cryptosystems
RSA
Diffie-Hellman key exchange algorithm
Digital Signature Standard (DSS)
Elliptic curve Cryptography(ECC)
Assymmetric Encryption Algorithms
Used for authenticating both source and data integrity
Digital Signatures
Protects a message without needing to first arrange for sender and receiver to have same secret key
Digital Envelopes
Keys for public-key algorithms
- stream key for symmetric stream cipher
Random Numbers
Randomness - uniform distribution; independence
Unpredicatability - each number is statistically independent of other numbers
Random Number Requirements
Cryptographic applications typically make use of algorithmic techniques for random number generation
Random vs Pseudorandom ( sequences produced that satisfy statistical randomness tests
