much computation. However, mathematicians have been trying (for other reasons) to solve this
equation for a long time, and many believe there is no shortcut to a solution.
key, more computation is required to solve the equation, and hence the message is more secure.
is the basis of the Digital Signature Standard (DSS), a U.S. Government document. As with
other digital signature algorithms, DSA lets one person with a secret key “sign” a document, so
that others with a matching public key can verify it must have been signed only by the holder of
the secret key.
message. They are called “one-way” because there is no known way (without infeasible
amounts of computation) to find a message with a given hash value. In other words, a hash value
can be determined for a given message, but it is not known to be possible to construct any
message with a given hash value. Hash functions are similar to the scrambling operations used
in symmetric key encryption, except that there is no decryption key: the operation is
irreversible. The result has a fixed length, which is 160 bits in the case of the Secure Hash
Algorithm (SHA) used by DSA.
themselves. Thus it is possible to sign a message’s hash value, without even knowing the
content of the message. This makes it possible to have digital notaries, who can verify a
document existed (and was signed), without the notary knowing anything about what was in the
document.