Practical UNIX and Internet Security, 3rd Edition

Understanding Cryptography

Cryptography is a collection of mathematical techniques for protecting information. Using cryptography, you can transform written words and other kinds of messages so that they are unintelligible to anyone who does not possess a specific mathematical key necessary to unlock the message. The process of using cryptography to scramble a message is called encryption . The process of unscrambling the message by use of the appropriate key is called decryption . Figure 7-1 illustrates how these two processes fit together.

Figure 7-1. Encryption and decryption

Cryptography is used to prevent information from being accessed by an unauthorized recipient. In theory, once a piece of information is encrypted, the encrypted data can be accidentally disclosed or intercepted by a third party without compromising the security of the information, provided that the key necessary to decrypt the information is not disclosed and that the method of encryption will resist attempts to decrypt the message without the key.

For example, here is a message that you might want to encrypt:

SSL is a cryptographic protocol

And here is how the message might look after it has been encrypted:

Ç'@%[»FÇ«;$TfiP∑|x¿EûóõÑ%ß+ö~·...aÜ"BÆuâw

Because the decryption key is not shown, it should not be practical to take the preceding line of gibberish and turn it back into the original message.

Roots of Cryptography ...