D-Link DFL-2500 User Guide - Page 214

20.2. Introduction to Cryptography 195 Another solution is required. From a connectivity and security perspective, Virtual Private Networks may still be viewed as "fixed connections" in that they do provide connectivity between two or more organizations. This is a fact that does not change even though Cryptography is deployed to implement the "Virtual" side of the "Private Network". 20.2 Introduction to Cryptography Cryptography provides a means to create "Virtual Private Networks" across the Internet with no additional investments in cables, leased lines, or other connectivity. It is an umbrella expression covering three basic techniques and benefits: Confidentiality No one but the intended recipients is able to intercept and understand the communication. Confidentiality is accomplished by encryption. Authentication & Integrity Proof for the recipient that the communication was actually sent by the expected sender, and that the data has not been modified in transit. This is accomplished by authentication, often by use of cryptographic keyed hashes. Non-repudiation Proof that the sender actually sent the data; the sender cannot later deny having sent it. Non-repudiation is usually a benign side-effect of authentication. 20.2.1 Encryption Encryption is a process of encoding sensitive information from plaintext to unreadable ciphertext through some mathematical algorithms. The operation of the algorithms is varied and usually parameterized by a large random number, known as a key. The ciphertext is encrypted by the key and it needs the same key or a related key to perform the reverse procedure - decryption, to return to the original plaintext. The algorithms of Encryption can be categorized into three types - symmetric, asymmetric, and hybrid encryption. D-Link Firewalls User's Guide