RSA Laboratories

2.2.1 What is privacy?

Privacy is perhaps the most obvious application of cryptography. Cryptography can be used to implement privacy simply by encrypting the information intended to remain private. In order for someone to read this private data, one must first decrypt it. Note that sometimes information is not supposed to be accessed by anyone, and in these cases, the information may be stored in such a way that reversing the process is virtually impossible. For instance, on a typical multi-user system, no one is supposed to know the list of passwords of everyone on the system. Often hash values of passwords are stored instead of the passwords themselves. This allows the users of the system to be confident their private information is actually kept private while still enabling an entered password to be verified (by computing its hash and comparing that result against a stored hash value).

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