Why Have Cryptography
Encryption is the science of changing data so that it is unrecognisable and useless to an unauthorised person. Decryption is changing it back to its original form.
The most secure techniques use a mathematical algorithm and a variable value known as a 'key'.
The selected key (often any random character string) is input on encryption and is integral to the changing of the data. The EXACT same key MUST be input to enable decryption of the data.
This is the basis of the protection.... if the key (sometimes called a password) is only known by authorized individual(s), the data cannot be exposed to other parties. Only those who know the key can decrypt it. This is known as 'private key' cryptography, which is the most well known form.
OTHER USES OF CRYPTOGRAPHY
Many techniques also provide for detection of any tampering with the encrypted data. A 'message authentication code' (MAC) is created, which is checked when the data is decrypted. If the code fails to match, the data has been altered since it was encrypted. This facility has may practical applications.
The Cryptography Management Toolkit is a resource specifically designed to introduce cryptography in detail. It includes presentations, a comprehensive guide book, check lists, source code for common algorithms, and various other items.
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