CCNAS V1.2 Chapter 07 Cryptographic Systems

A network can be secured through device hardening, AAA access control, firewall features, and IPS implementations. These combined features protect the infrastructure and end devices within the local network. But how is network traffic protected when traversing the public Internet? The answer is through cryptographic methods.

The principles of cryptology can be used to explain how modern day protocols and algorithms are used to secure communications. Cryptology is the science of making and breaking secret codes. The development and use of codes is called cryptography, and breaking codes is called cryptanalysis. Cryptography has been used for centuries to protect secret documents. For example, Julius Caesar used a simple alphabetic cipher to encrypt messages to his generals in the field. His generals would have knowledge of the cipher key required to decrypt the messages.

Today, modern day cryptographic methods are used in multiple ways to ensure secure communications. For example, many modern networks ensure authentication with protocols, such as hash message authentication code (HMAC). Integrity is ensured by implementing either MD5 or SHA hash generating algorithms. Data confidentiality is ensured through symmetric encryption algorithms, including DES, 3DES, and AES, or asymmetric algorithms, including RSA and the public key infrastructure (PKI).

Symmetric encryption algorithms are based on the premise that each communicating party knows the pre-shared key. Asymmetric encryption algorithms are based on the assumption that the two communicating parties have not previously shared a secret and must establish a secure method to do so.