Chapter 4. Site-to-Site VPNs
This section covers the key topics of cryptography. You should understand these principles before studying VPN technologies.
Cryptology is the science of making and breaking secret codes. A cipher is an algorithm for performing encryption and decryption. The Vigenère cipher is a polyalphabetic cipher that encrypts text by using a series of different Caesar ciphers based on the letters of a keyword.
Cryptanalysis is the practice of breaking codes to obtain the meaning of encrypted data. Following are examples of attacks:
• Brute-force attack: The attacker tries every possible key with the decryption algorithm.
• A cipher-text-only attack: The attacker has the cipher text of several messages ...