# Symmetric Encryption

## Symmetric Encryption

by Cyrus Lok on Friday, January 8, 2010 at 12:57am
1. Faster than asymmetric encryption.

2. Stronger than asymmetric encryption, hence the key length is also shorter than asymmetric encryption.

3. One key is used for encryption and decryption.

4. key length is between 40-bit and 256-bit

Example of symmetric encryption:

1. Data Encryption Standard (DES): 56-bit

2. Triple DES (3DES): 112-bit and 168-bit
It is known as triple DES because the algorithm is applied 3 times to a plaintext block. Encrypt-Decrypt-Encrypt method must be used to effectively increase the key length. Encrypting a plaintext block 3 times with different DES key will not increase the key length significantly at most it will be a 58-bit.
To encrypt:
|kns| >> |Encrypt with K1| >> |#\$%^| >> |Decrypt with K2| >> |adsfg| >> |Encrypt with K3| >> |@#\$%|

If K1 and K2 are the same encryption key then the maximum key length is 112-bit, if K1 and K3 are different encryption key then 168-bit key length will be achieved

To decrypt:
|@#\$%| >> |Decrypt with K3| >> |adsfg| >> |Encrypt with K2| >> |#\$%^| >> |Decrypt with K1| >> |kns|

3. Advanced Encryption Standard (AES): 128-bit, 192-bit and 256-bit
(Please see flash demonstration http://www.cs.bc.edu/~straubin/cs381-05/blockciphers/rijndael_ingles2004.swf)

4. Internation Data Encryption Algorithm (IDEA): 128-bit

5. Rivest Cipher (RC) series
5a. RC2: 40-bit and 64-bit
5b. RC4: from 1-bit to 256-bit
5c. RC5: from 0-bit to 2040-bit
5d. RC6: 128-bit, 192-bit and 256-bit

Sidetrack: Ronald Rivest is a genius in cryptography many encryption algorithms and hashing functions used today were creation from him. Hash functions such as MD2,MD4,MD5,MD6. Encryption algorithms: Rivest Cipher series (RC6 was solely created by him to compete with AES for bidding the standard encryption to replace DES), RSA (partially by him, RSA stands for Rivest, Shamir, Aldeman; These scientists met in MIT and created this asymmetric encryption RSA. My secure shell vty connection is using RSA to encrypt the ssh session)

6. Blowfish: from 32-bit to 448-bit