ref: dab539cd14726de15932b0310532212f8da29bf7
dir: /sys/src/cmd/python/Doc/lib/libsha.tex/
\section{\module{sha} --- SHA-1 message digest algorithm} \declaremodule{builtin}{sha} \modulesynopsis{NIST's secure hash algorithm, SHA.} \sectionauthor{Fred L. Drake, Jr.}{[email protected]} \deprecated{2.5}{Use the \refmodule{hashlib} module instead.} This module implements the interface to NIST's\index{NIST} secure hash algorithm,\index{Secure Hash Algorithm} known as SHA-1. SHA-1 is an improved version of the original SHA hash algorithm. It is used in the same way as the \refmodule{md5} module:\ use \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 concatenation of the strings fed to it so far.\index{checksum!SHA} SHA-1 digests are 160 bits instead of MD5's 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}{digest_size} The size of the resulting digest in bytes. This is always \code{20}. \end{datadesc} An sha object has the same methods as md5 objects: \begin{methoddesc}[sha]{update}{arg} Update the sha object with the string \var{arg}. Repeated calls are equivalent to a single call with the concatenation of all the arguments: \code{m.update(a); m.update(b)} is equivalent to \code{m.update(a+b)}. \end{methoddesc} \begin{methoddesc}[sha]{digest}{} Return the digest of the strings passed to the \method{update()} method so far. This is a 20-byte string which may contain non-\ASCII{} characters, including null bytes. \end{methoddesc} \begin{methoddesc}[sha]{hexdigest}{} Like \method{digest()} except the digest is returned as a string of length 40, containing only hexadecimal digits. This may be used to exchange the value safely in email or other non-binary environments. \end{methoddesc} \begin{methoddesc}[sha]{copy}{} Return a copy (``clone'') of the sha object. This can be used to efficiently compute the digests of strings that share a common initial substring. \end{methoddesc} \begin{seealso} \seetitle[http://csrc.nist.gov/publications/fips/fips180-2/fips180-2withchangenotice.pdf] {Secure Hash Standard} {The Secure Hash Algorithm is defined by NIST document FIPS PUB 180-2: \citetitle[http://csrc.nist.gov/publications/fips/fips180-2/fips180-2withchangenotice.pdf] {Secure Hash Standard}, published in August 2002.} \seetitle[http://csrc.nist.gov/encryption/tkhash.html] {Cryptographic Toolkit (Secure Hashing)} {Links from NIST to various information on secure hashing.} \end{seealso}