Chapter 8: Cryptography Flashcards
Substitution Ciphers
You change one symbol with another.
- The Caesar Cipher shifted 3 letters to the right in Latin.
- The less cryptotext that’s available, the harder it is to decrypt
Multi-Alphabet Substitution Cipher
Maybe shifting differently, say 3 to the right, 2 to the right, 1 to the left, in that order.
- Vigenère Cipher
- You had a table of letters matched up to keywords
Transposition Ciphers
Take separate blocks of text and scramble them all differently
Rot13
Rotates every letter 13 places in the alphabet
The Enigma Machine
A typewriter that used a different substitute or alphabet for each keystroke
-Contained 26 different alphabets and was very hard to break back in the day.
Steganography
Hiding a message within an image, audio file, or some other file
- Least significant bit is the most common
- You change the last bit in every byte
- Invisible secrets is a good application for steganography
How to encrypt in SUSE
Login as root and start YaST
System->partitioner
Answer yes, select filesystem, click edit
Select encrypt
Symmetric encryption algorithm
- Both ends of the message must have the same key and processing algorithms
- Generates a (symmetric, secret, private) key that’s disclosed only to those who need to know
- faster than asymmetric, just as secure with smaller key size
- Problem is, if you need to share the key, how do you do it securely?
Block Cipher
Algorithm works on chunks of data
Stream Cipher
Algorithm works by bit or by byte
in-band vs. out of band Key Exchange
In-band
-Key is included with the data stream (IPSec)
Out of Band
-Another channel shares the key
Key Exchange Forward Secrecy
- Ensures that if one key is compromised, subsequent keys will not be
- Perfect forward secrecy is when a key is unbreakable
Data Encryption Standard (DES)
-Was the standard used by government from the 70s until it was replaced by AES
-It was based on a 56-bit key
Symmetric Encryption
Triple-DES (3DES)
-Uses 3 56-bit DES keys; 168 bits
-Pretty decent, though AES is still generally preferred
Symmetric Encryption
Advanced Encryption Standard (AES)
-Uses the Rijndael algorithm, developed by Daemen and Rijma
-128 bit key is standard, 192 and 256 are optional
-256 bit is for DoD TS information
Symmetric Encryption
Carlisle Adams and Stafford Tavares (CAST)
-Used by MS and IBM
-Fast, efficient 40-128 bit key
-128 and 256 exist, too
Symmetric Encryption
Ron’s Cipher (RC)
-Developed by RSA, it’s very strong. RC4, 5, and 6. 6 is up to 2-48 bit
-RC4 is popular with wireless encryption. Streaming cipher with 40-2048 bits
-used in SSL and TLS
-Used for downloading Bittorrent files, too
Symmetric Encryption
Blowfish and Twofish
Blowfish, 64 bit block cipher, very fast
-Symmetric block cipher, 32-448 bit keys
Two fish works on 128-bit blocks. Complex key schedule
Symmetric Encryption
international Data Encryption Algorithm (IDEA)
-Developed by the Swiss. 128-bit key
-Used by PGP
Symmetric Encryption
One-Time Pads
The key’s as long as a plaintext message
-The key can only be used once, then it’s discarded
Rivest, Shamir, Adleman (RSA)
Pretty much the standard for Asymmetric encryption, as old as it is
Diffie-Hellman
Founders of public/private keys
-Only used for the creation of a symmetric key between two parties
Asymmetric Encryption
<b>If you’re asked about insecure key exchange, it’s this or IPSec</b>
Elliptic Curve Cryptography (ECC)
-Smaller keys than RSA, same level of security
-This may start replacing RSA as the de facto standard
Asymmetric Encryption
ElGamal
Uses an ephemeral key, one that lasts only for one session
