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Designing Active Server Pages by Scott Mitchell

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Encrypting Information

Encryption is the process of taking a legible piece of information, such as a text file or Word document, and converting it into a scrambled, unreadable version. The process of converting the scrambled version back into a readable version is referred to as decryption . Encryption is commonly used in sending sensitive information over an insecure medium. Every communication medium is potentially insecure, and the Internet’s communication channels are no exception.

Encryption algorithms commonly use a key when encrypting the information. This key helps ensure that only the intended recipient of the message can decrypt the message. When sending a sensitive message, the following steps should be taken:

  1. Before sending the sensitive message, encrypt it into an unreadable form using a key.

  2. Send the encrypted message over the insecure communication medium.

  3. The intended recipient of the message has a key that will decrypt the message, converting it from the unreadable, scrambled form back into the readable version that existed prior to Step 1. Once he receives this message, it is decrypted and read.

There are several potential weak points in these three steps. The key used in Step 1 to encrypt the message is nothing more than a collection of bits (be it a number, textual password, or some other key). These keys must be of a finite size; since they are a finite size, there is obviously a finite number of potential keys. If a rogue developer intercepts the encrypted message, ...

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