System Security:Cryptography Technologies

CPE 261403 - Operating Systemshttp://www.e-cpe.org/moodle

What does the fish mean?

Ichthys

User name / Password

Threat Ex: Wifi Packet Sniffers

Protection with Cryptography

Encryption and Decryption

Symmetric – Uses a shared key

Asymmetric – Added security with Public and Private keys

Symmetric Encryption

I LOVE YOU

Simple example: Add a constant to the ASCII value

J MPWF ZPVKey = 1

Some Examples Data Encryption Standard (DES)

56 bit key for every 64 bit value

Advanced Encryption Standard (AES) 256 bit key for every 128 bit value

RC4 As used in WEP (Wired Equivalent Privacy)

WPA, WPA2 (Wi-Fi Protected Access) 256 bit key

Asymmetric Encryption

Algorithm Example

Public Key = (kd, N)

Private Key = (ke, N)

N = p.q (where p, q are prime numbers) Pick kd that is < N Calculate ke where

ke.kd mod (p-1)(q-1) = 1

Example If p = 7 and q = 13 N = 7.13 = 91

Pick Kd = 5 Find Ke

Ke.5 mod (7-1)(13-1) = 1 Ke = 29

Public Key = (5, 91)Private Key = (29, 91)

Encrypting and Decrypting

Encrypt message = (input ^ ke ) mod N Decrypt message = (input ^ kd) mod N

If we want to send the number 69

Encrypted message = 69 ^ 5 mod 91 = 62

Decrypted message = 62 ^ 29 mod 91 = 69

*Note: number must < N

Notes

In reality p and q can be 512 bits each