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Network Security with OpenSSL by Pravir Chandra, Matt Messier, John Viega

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Digital Signature Algorithm (DSA)

The DSA algorithm was developed by the National Institute for Standards and Testing (NIST) and the National Security Agency (NSA). It was first proposed in 1991 and stirred up a significant amount of controversy. Finally, in 1994, it became a standard. As its name implies, the DSA algorithm is useful for computing digital signatures, but that is the only thing for which it can be used. It is not capable of providing key agreement or encryption without extension.

Using a private key, the user can compute a signature for an arbitrary piece of data. Anyone possessing the public key that corresponds to the private key used to compute a signature can then verify that signature. The algorithm works in conjunction with the Secure Hash Algorithm (SHA). Essentially, the hash of the data to be signed is computed, and the hash is actually signed, rather than the data itself. The public key that corresponds to the private key used to compute a digital signature can then be used to obtain the hash of the data from the signature. This hash is compared with the hash computed by the party verifying the signature. If they match, the data is considered authentic. If they don't match, the data is not identical to the data that was originally signed.

A digital signature is useful for verifying the integrity of data, ensuring that it has not been corrupted or tampered with. It also provides non-repudiation since only one person should have access to the private key ...

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