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Encryption by Mind Map: Encryption
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Ron Rivest

RSA Security

variable length stream cipher



most common stream cipher used today

used in:






many others

symmetric encryption algorithm

operate on smaller units of plaintext (bits)

much faster than block ciphers

operate on large blocks of data


stream cipher operation

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

keystream generation can be independent of:



yields synchronous stream cipher

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

capable of key lengths

up to 256 bits

typically, 64 bits, 128 bits, 256 bits

considered moderately secure

WEP has been broken!

WEP is weak, not RC4

TKIP, fixes problems with WEP, still uses RC4


Ron Rivest

RSA Security

developed in 1994

block cipher


most well-known

developed for use in software

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

parameterized algorithm


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)

3 routines

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


exceptionally simple

easy to implement and analyze

July 14, 2002


broke 64-bit RC5 key

1757 days of computation

~ 59 billion keys tested

peak rate 270 million keys per second

December 3, 2002

project to break 72-bit RC5


Data Encryption Standard


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

various shortcut attacks found

computers speed

encrypts and decrypts in 64-bit blocks

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

56-bit not appropriate for high security apps

abandoned by NIST in 1997

began work on replacement - AES

still widely used


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


Start with plaintext block

Encrypt with Key 1

Decrypt with Key 2

Encrypt with Key 3

Output Ciphertext block

Decrypt in reverse

All Keys should be different

8 parity bits for each key = 168 bit effective strength


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