Section 2: Cryptography Flashcards
What is obfuscation?
Hide something to make it confidential.
Explain the Caesar Cipher
Substitute a letters
What is ROT2?
Shifted the letters along 2 places.
A becomes C
Vigenere Cypher
A key is used on the plain text and then matched against a caesar cypher table. Great for the alphabet.
What are the 2 classic cryptography components?
- Algorithm
2. Key for encryption
XOR - Exclusive OR
Similar to vigenere but for binary
What is Kerckhoffs’s principle?
Everybody knows the algorithm but the key is secure.
What is data at rest?
Stored media
What is data in transit?
Phone calls etc
What is Data in Process?
Data in RAM, CPU
How do you send an encryption key?
asymmetric encryption
In-band v out-of-band
Sending the key with the encrypted data, vs physically taking.
What is an Ephemeral Key?
Temporary Key - provides perfect forward secrecy.
What is asymmetric encrption?
Uses a key pair - public + private.
Public used to encrypt
Private used to decrypt
Slow and onerous. Great for exchanging session keys.
What is a Cryptosystem?
Sets the rules of the system - key properties - length. Communications requirements for key exchange and the actions for encryption and decryption.
What is symmetric encrption?
Using the same key to encrypt and decrypt.
What is DES
Data Encryption Standard - a symmetric block algorithm, invented by IBM. First open standard by gov.
How does DES work?
64 block Create a key and subkey Perform Feistel Function Expansion function XOR 8 S Boxes Final permutation
What types of block encryption replaced DES?
Blowfish and Triple DES.
What 3 things are important for a block cypher?
Key size
Number of rounds
Block size
What are DES stats?
64-bit Block size
16 Rounds
56 bit Key Size
What are Triple DES stats?
64-bit Block size
16 Rounds
x3 56 bit Key Size
What are the Blowfish stats?
64-bit Block size
16 Rounds
32 - 448 bit Key Size
What is the AES? When did it come out?
Advanced Encryption Standard released in early 2000s. Unhackable! Supported by the NIST.
What are AES stats?
128-bit Block size
10, 12 or 14 Rounds
128, 192 or 256 bit Key Size
What is a Streaming Cypher?
Each bit is encrypted one by one.
What is RC4?
Rivest Cipher 4
Streaming Cypher
No Blocks, 1 Round, Key Size 40 to 2048-bits
