CSC405 Introduction to Computer Security
Introduction to Cryptography and Secret Key Cryptography
Portions of the material for this lecture are taken from “Designing Network Security, 2
Merike Kaeo, Cisco System”
*Material for this lecture has been borrowed from the class textbook Network Security and from
Dr. Khaled Harfoush, DES Spring 2005 lecture notes.
Keywords: symmetric key encryption, asymmetric encryption, hash functions, digital signatures,
authentication & authorization, key management, key escrow
Cryptography is the basis for secure communications; it is; therefore, important that you understand three
basic cryptographic functions: symmetric encryption, asymmetric encryption, and one-way hash functions.
Most current authentication, integrity, and confidentiality technologies derive from these three
is the science of writing or reading codes messages; it is the basic building block that
enables the mechanisms of authentication, integrity, and confidentiality.
ensures that no one except the sender and receiver of the data can actually understand
ensures that the data has not been altered in transit
establishes the identity of either the sender or the receiver of information or both. In some
communication instances, it is not always a requirement to have mutual authentication of both parties.
plaintext/cleartext – a message’s original form that is not encrypted
ciphertext – the mangled information
encryption -- the process for producing ciphertext from plaintext
decryption -- the process for production plaintext from ciphertext
A cryptographic key
is a digital object that you can use to encrypt, decrypt, and sign information.
To Publish or Not to Publish
Common practice today is for most commercial cryptosystems to be published and for military
cryptosystems to be kept secret.
Background / History
Egyptians 3,000 BC
A Spartan Scytale
Krutz, Ronald; Vines, Russell Dean; The CISSP Prep Guide: Mastering the CISSP and ISSEP Exams, Second
Edition, p. 208