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Practical Web Technologies by V. Lau, P. K. Yuen

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19.1. Basic data security

19.1.1. Cryptography: encryption and decryption

Even in the ancient world, people were fully aware of the importance of data security. Important messages were usually disguised or hidden from anyone for whom they were not intended. For example, messages were often encrypted with substitution methods or written in special ink visible only under heat. These are the ancestors of the encryption, or more precisely cryptographic, technologies today.

In general, any technique that can transform a readable document (or plain text) into unreadable gibberish is called encryption. The data after the encryption are known as ciphertext (or cipher). Under this definition, almost any text transformation methods including compression ...

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