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.\"
.IX Title "Digest::MultiHash 3pm"
.TH Digest::MultiHash 3pm "2009-10-19" "perl v5.18.1" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.SH "NAME"
Digest::MultiHash \- XOR based, variable width multiplexing of hashes (a
generalized Digest::SV1).
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&        use Digest::MultiHash;
\&
\&        my $d = Digest::Multihash\->new(
\&                width => 16, # bytes
\&                hashs => ["SHA\-512", "Whirlpool"], # see below for arbitrary arguments
\&        );
\&
\&        $d\->add($data);
\&
\&        print $d\->hexdigest;
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This class inherits from Digest::base, and provides generalized digest
multiplexing.
.PP
It will multiplex all calls to \f(CW\*(C`add\*(C'\fR to all of it's sub digest objects.
Likewise, when the final digest is extracted the digests will be extracted and
then \s-1XOR\s0'd over eachother according to \f(CW\*(C`width\*(C'\fR.
.PP
\&\f(CW\*(C`width\*(C'\fR will default to the width of the first hash if unspecified.
.PP
\&\f(CW\*(C`hashes\*(C'\fR defaults to \f(CW\*(C`SHA\-1\*(C'\fR for compatibility reasons.
.PP
This module is useful for generating keys from passphrases, by supplying the
desired width and simply making sure there is enough data from the combined
hashes.
.SH "METHODS"
.IX Header "METHODS"
See Digest for the complete \s-1API.\s0 This module inherits from Digest::base.
.IP "new" 4
.IX Item "new"
This methods accepts a hash reference or an even sized list of parameters named
according to the methods.
.IP "add" 4
.IX Item "add"
.PD 0
.IP "digest" 4
.IX Item "digest"
.PD
Compute the hash by calling \f(CW\*(C`digest\*(C'\fR on all of the subhashes, splitting the
result up into \f(CW\*(C`width\*(C'\fR sized chunk, and then XORing these together.
.Sp
If the result is not aligned on \f(CW\*(C`width\*(C'\fR the result will not be truncated. The
shorter string will still be \s-1XOR\s0'd with the hash, even if this only affects
part of the result.
.Sp
If there are not at least \f(CW\*(C`width\*(C'\fR bytes of data in the output of the combined
hashes an error is thrown.
.IP "clone" 4
.IX Item "clone"
Clones the hash.
.IP "hashes" 4
.IX Item "hashes"
Get the array of hashes to use. Array values in this will be dereferenced
before the call to \*(L"new\*(R" in Digest to allow passing of arbitrary arguments.
Blessed objects (of any class) will be used verbatim.
.Sp
The list of hashes cannot be changed after construction.
.IP "width" 4
.IX Item "width"
Get/set the byte-width to use.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Digest, Digest::SV1, Digest::SHA1