\section{\module{sha} ---

SHA message digest algorithm}

\declaremodule{builtin}{sha}

\modulesynopsis{NIST's secure hash algorithm, SHA.}

\sectionauthor{Fred L. Drake, Jr.}{[email protected]}

This module implements the interface to NIST's\index{NIST} secure hash

algorithm,\index{Secure Hash Algorithm} known as SHA. It is used in

the same way as the \refmodule{md5} module:\ use the \function{new()}

to create an sha object, then feed this object with arbitrary strings

using the \method{update()} method, and at any point you can ask it

for the \dfn{digest} of the contatenation of the strings fed to it

so far.\index{checksum!SHA} SHA digests are 160 bits instead of 128

bits.

\begin{funcdesc}{new}{\optional{string}}

Return a new sha object. If \var{string} is present, the method

call \code{update(\var{string})} is made.

\end{funcdesc}

The following values are provided as constants in the module and as

attributes of the sha objects returned by \function{new()}:

\begin{datadesc}{blocksize}

Size of the blocks fed into the hash function; this is always

\code{1}. This size is used to allow an arbitrary string to be

hashed.

\end{datadesc}

\begin{datadesc}{digestsize}

The size of the resulting digest in bytes. This is always

\code{20}.

\end{datadesc}

A sha object has all the methods the md5 objects have, plus one:

\begin{methoddesc}[sha]{hexdigest}{}

Return the digest value as a string of hexadecimal digits. This may

be used to exchange the value safely in email or other non-binary

environments.

\end{methoddesc}

\begin{seealso}

\seetext{The Secure Hash Algorithm is defined by NIST document FIPS

PUB 180-1: \emph{Secure Hash Standard}, published in April

of 1995. It is available online as plain text at

\url{http://csrc.nist.gov/fips/fip180-1.txt} (at least one

diagram was omitted) and as PostScript at

\url{http://csrc.nist.gov/fips/fip180-1.ps}.}

\end{seealso}