84 lines
3.0 KiB
TeX
84 lines
3.0 KiB
TeX
\section{\module{sha} ---
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SHA-1 message digest algorithm}
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\declaremodule{builtin}{sha}
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\modulesynopsis{NIST's secure hash algorithm, SHA.}
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\sectionauthor{Fred L. Drake, Jr.}{fdrake@acm.org}
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This module implements the interface to NIST's\index{NIST} secure hash
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algorithm,\index{Secure Hash Algorithm} known as SHA-1. SHA-1 is an
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improved version of the original SHA hash algorithm. It is used in
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the same way as the \refmodule{md5} module:\ use \function{new()}
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to create an sha object, then feed this object with arbitrary strings
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using the \method{update()} method, and at any point you can ask it
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for the \dfn{digest} of the concatenation of the strings fed to it
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so far.\index{checksum!SHA} SHA-1 digests are 160 bits instead of
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MD5's 128 bits.
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\begin{funcdesc}{new}{\optional{string}}
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Return a new sha object. If \var{string} is present, the method
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call \code{update(\var{string})} is made.
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\end{funcdesc}
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The following values are provided as constants in the module and as
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attributes of the sha objects returned by \function{new()}:
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\begin{datadesc}{blocksize}
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Size of the blocks fed into the hash function; this is always
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\code{1}. This size is used to allow an arbitrary string to be
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hashed.
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\end{datadesc}
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\begin{datadesc}{digest_size}
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The size of the resulting digest in bytes. This is always
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\code{20}.
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\end{datadesc}
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An sha object has the same methods as md5 objects:
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\begin{methoddesc}[sha]{update}{arg}
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Update the sha object with the string \var{arg}. Repeated calls are
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equivalent to a single call with the concatenation of all the
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arguments: \code{m.update(a); m.update(b)} is equivalent to
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\code{m.update(a+b)}.
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\end{methoddesc}
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\begin{methoddesc}[sha]{digest}{}
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Return the digest of the strings passed to the \method{update()}
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method so far. This is a 20-byte string which may contain
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non-\ASCII{} characters, including null bytes.
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\end{methoddesc}
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\begin{methoddesc}[sha]{hexdigest}{}
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Like \method{digest()} except the digest is returned as a string of
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length 40, containing only hexadecimal digits. This may
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be used to exchange the value safely in email or other non-binary
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environments.
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\end{methoddesc}
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\begin{methoddesc}[sha]{copy}{}
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Return a copy (``clone'') of the sha object. This can be used to
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efficiently compute the digests of strings that share a common initial
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substring.
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\end{methoddesc}
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\begin{seealso}
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\seetitle[http://csrc.nist.gov/publications/fips/fips180-1/fip180-1.txt]
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{Secure Hash Standard}
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{The Secure Hash Algorithm is defined by NIST document FIPS
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PUB 180-1:
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\citetitle[http://csrc.nist.gov/publications/fips/fips180-1/fip180-1.txt]
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{Secure Hash Standard}, published in April of 1995. It is
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available online as plain text (at least one diagram was
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omitted) and as PDF at
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\url{http://csrc.nist.gov/publications/fips/fips180-1/fip180-1.pdf}.}
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\seetitle[http://csrc.nist.gov/encryption/tkhash.html]
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{Cryptographic Toolkit (Secure Hashing)}
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{Links from NIST to various information on secure hashing.}
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\end{seealso}
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