CSC 386 – Computer Security

Scott Heggen

Agenda

• Emmanuel Tachu will present his work from an independent study on Networking• Cryptography Primer

Last Week’s Homework

• Bell-LaPadula Model• Deadline extended until 11:55pm today

Cryptography Primer

Alice Bob

m

Eve

Cryptography Primer

Alice Bob

Eve

k k

m EC = E(k,m)

mD

Symmetric Key

• Both Alice and Bob’s key are the same• Must be shared prior to communications• What is the key?

Substitution Cipher (Caesar Cipher)

A C

B E

C F

D G

E H

F I

G J

… …

k = Alice Bob

Eve

k k

“bad egg” EC = E(k,m) = “egc hjj”

“bad egg”D “egc hjj”

Assignment

• For Friday:• Create a Python script which takes in two files: message.txt and key.txt• The message.txt file can contain any message you chose to send me• The key.txt file must contain your B-number, without the letter B• The Python script must compute C using the message and the key. Your

encryption algorithm E should be a simple substitution cipher which shifts each letter of message by the integer value in key.

• Submit to Moodle:• Your Python Script• coded_message.txt