10 April 2016


by mo

Notes from CPNT-250 course at SAIT.

Cryptography: provides us with both the mechanism and confidence to

store and transmit our most sensitive digital information.

  • plain text: original unencrypted message.
  • cryptographic algorithm: method used to encrypt the message.
  • cipher text: encrypted text.
  • Encryption: process of converting plain text into cypher text.
  • Decryption: process of converting cyper text into plain text.
  • Key: data used to encrypt/decrypt information.

Symetric Key Cryptography

When same key is used for both encryption and decryption. Also referred to as private key cryptography.

Asymmetric/Public Key Cryptography

User different keys for encryption and decryption. Each user generates a pair of keys. A private key is used to decrypt and a public key is used to encrypt.

$ echo 'secret' > secret.txt
$ gpg -c secret.txt
$ gpg -d secret.txt


Hiding a secret message within an ordinary message and the extraction of that message at its destination. The goal is not to hide the content of a message, but to hide the existence of a message.

There are two files composing the finished stego file or stego object.

The file that contains the secret message is called the carrier file or cover object. The embedded secret document or message is sometimes called the payload.

$ echo secret > secret.txt
$ cat secret.txt >> image.png
$ tail -c 7 image.png

The Deep Web

Large portion of data available on the web is present in the so called deep web (or hidden web);

Tor is a free tool that allows people to use the internet anonymously. Tor anonymizes the origin of the internet traffic. Install the Tor browser and/or download TAILS tails.boum.org.