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Encryption
by Michael Qaissaunee
# Encryption

## RC4

### Ron Rivest

### RSA Security

### variable length stream cipher

### fast

### efficient

### most common stream cipher used today

### used in:

### symmetric encryption algorithm

### operate on smaller units of plaintext (bits)

### much faster than block ciphers

### stream cipher operation

### keystream generation can be independent of:

### capable of key lengths

### considered moderately secure

## RC5

### Ron Rivest

### RSA Security

### developed in 1994

### block cipher

### developed for use in software

### extremely efficient on "fast" processors (Pentium and above)

### parameterized algorithm

### variable

### 3 routines

### exceptionally simple

### easy to implement and analyze

### July 14, 2002

### December 3, 2002

## DES

### Data Encryption Standard

### 56-bit

### modified version of IBMs Lucifer algorithm (128-bit)

### adopted by NIST as federal standard November 23, 1976

### specification published in January 1977

### quickly became widely-employed

### find DES key by brute force

### encrypts and decrypts in 64-bit blocks

### 56-bit not appropriate for high security apps

### abandoned by NIST in 1997

### began work on replacement - AES

### still widely used

## 3DES

### DES developed by IBM around 1974

### adopted as national standard in 1977

### 3DES minor variation of this

### 3 times slower than DES

### far more secure than DES

### 3 64-bit keys = 192 bit overall length

### same procedure as DES but repeated 3 times

### procedure

### All Keys should be different

### 8 parity bits for each key = 168 bit effective strength

## AES

### Advanced Encryption Standard

### NIST initiated selection in 1997

### symmetric-key encryption

### for unclassified Federal information

### initial candidates

### Selected Rijndael "Rhine-Dahl"

### intended to be several orders of magnitude more secure than DES only marginally slower

### expected to have a life of 20-30 years

### will require new APs and wireless NICs

### CPU intensive

### included in IEEE 802.11i draft

### capable of 128, 192 and 256-bit keys

### considered uncrackable

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WEP

TKIP

SSL

TLS

MPPE

many others

operate on large blocks of data

slow

operate on smaller units of plaintext (usually bits)

generates a keystream

sequence of bits used as a key

combine keystream with plaintext

bitwise XOR operation

plaintext

ciphertext

yields synchronous stream cipher

otherwise called self-synchronizing, depend on, data, encryption

up to 256 bits

typically, 64 bits, 128 bits, 256 bits

WEP has been broken!

WEP is weak, not RC4

TKIP, fixes problems with WEP, still uses RC4

fastest

most well-known

block size, 32 bits (experimentation/evaluation), 64 bits (drop-in replacement for DES), 128 bits

key size (0 to 2040 bits)

number of rounds (0 to 255)

key expansion, user-provided secret key, expanded to fill key table, size depends on number of rounds, key table used for encryption/decryption

encryption, integer addition, bitwise XOR, variable rotation

decryption

Distributed.Net

broke 64-bit RC5 key

1757 days of computation

~ 59 billion keys tested

peak rate 270 million keys per second

project to break 72-bit RC5

various shortcut attacks found

computers speed

every 8th bit used for parity

effective key strength = 56 bits

takes 64-bit plaintext block as input

outputs 64-bit ciphertext block

has 16 rounds

# rounds exponentially proportional to time required to crack

Start with plaintext block

Encrypt with Key 1

Decrypt with Key 2

Encrypt with Key 3

Output Ciphertext block

Decrypt in reverse

MARS

RC6

Rijndael

Serpent

Twofish