Flashcards in Chapter 8: Cryptography Deck (82)

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1

## Substitution Ciphers

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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

2

## Multi-Alphabet Substitution Cipher

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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

3

## Transposition Ciphers

### Take separate blocks of text and scramble them all differently

4

## Rot13

### Rotates every letter 13 places in the alphabet

5

## The Enigma Machine

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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.

6

## Steganography

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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

7

## How to encrypt in SUSE

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Login as root and start YaST

System->partitioner

Answer yes, select filesystem, click edit

Select encrypt

8

## Symmetric encryption algorithm

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-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?

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## Block Cipher

### Algorithm works on chunks of data

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## Stream Cipher

### Algorithm works by bit or by byte

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## in-band vs. out of band Key Exchange

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In-band

-Key is included with the data stream (IPSec)

Out of Band

-Another channel shares the key

12

## Key Exchange Forward Secrecy

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-Ensures that if one key is compromised, subsequent keys will not be

-Perfect forward secrecy is when a key is unbreakable

13

## Data Encryption Standard (DES)

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-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

14

## Triple-DES (3DES)

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-Uses 3 56-bit DES keys; 168 bits

-Pretty decent, though AES is still generally preferred

Symmetric Encryption

15

## Advanced Encryption Standard (AES)

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-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

16

## Carlisle Adams and Stafford Tavares (CAST)

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-Used by MS and IBM

-Fast, efficient 40-128 bit key

-128 and 256 exist, too

Symmetric Encryption

17

## Ron's Cipher (RC)

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-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

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## Blowfish and Twofish

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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

19

## international Data Encryption Algorithm (IDEA)

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-Developed by the Swiss. 128-bit key

-Used by PGP

Symmetric Encryption

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## One-Time Pads

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The key's as long as a plaintext message

-The key can only be used once, then it's discarded

21

## Rivest, Shamir, Adleman (RSA)

### Pretty much the standard for Asymmetric encryption, as old as it is

22

## Diffie-Hellman

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Founders of public/private keys

-Only used for the creation of a symmetric key between two parties

Asymmetric Encryption

**If you're asked about insecure key exchange, it's this or IPSec**

23

## Elliptic Curve Cryptography (ECC)

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-Smaller keys than RSA, same level of security

-This may start replacing RSA as the de facto standard

Asymmetric Encryption

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## ElGamal

### Uses an ephemeral key, one that lasts only for one session

25

## Kerchoff's Principle

### The security depends on the secrecy of the key, no the algorithm

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## Hashing Algorithms

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-Cannot be reversible

-No matter how many characters you input, the hash size is the same

-Few/no collisions

27

## Secure Hashing Algorithm (SHA)

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-160-bit, used with encryption protocols

-SHA-2: 224, 256, 334, 512 bit

-SHA-3 is out, but SHA-2 is pretty much flawless, so...

28

## Message Digest Algorithm (MD)

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Used to maintain integrity

-MD5, 4, 2. MD4 was used by NTLM

-MD5 produces a 128-bit hash, but it's very secure. Doesn't have strong collision resistance, so don't use it

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## RIPEMD (160, 256, 320)

### Based on MD4

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