Security (2) Flashcards
1
Q
What is symmetric key cryptography?
A
Alice and Bob share the same (symmetric) key: Ks
2
Q
What is a Substitution Cipher?
A
Substitute one thing for another
3
Q
What are Block Ciphers?
A
- Message is broken into blocks
- Each block is encrypted / decrypted separately
4
Q
What is Cipher Block Chaining?
A
- First block is XOR’d with an arbitrary number known by both parties (initialization vector or IV)
- Following blocks are XOR’d with previous block
- Decryption: apply the substitution using Ks, then XOR with previous block
5
Q
What is DES?
A
Data Encryption Standard
6
Q
Is DES considered secure?
A
- No - can be brute forced in less than a day
7
Q
How does DES work?
A
- 56-bit symmetric key, 64-bit plaintext input
- Block cipher: substitution derived from symmetric key
- Cipher block chaining: initial number derived from symmetric key
8
Q
Which is more secure: AES or DES?
A
- AES
- Brute force decryption that takes 1 second for DES takes 149 trillion years for 128-bit AES
9
Q
What is AES?
A
Advanced Encryption Standard
10
Q
How does AES Work?
A
- Symmetric key
- 128 bit block cipher
- 128, 192, or 256-bit key
