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.\" ========================================================================
.\"
.IX Title "Crypt::DSA 3pm"
.TH Crypt::DSA 3pm "2022-06-12" "perl v5.34.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
Crypt::DSA \- DSA Signatures and Key Generation
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\&    use Crypt::DSA;
\&    my $dsa = Crypt::DSA\->new;
\&
\&    my $key = $dsa\->keygen(
\&                   Size      => 512,
\&                   Seed      => $seed,
\&                   Verbosity => 1
\&              );
\&
\&    my $sig = $dsa\->sign(
\&                   Message   => "foo bar",
\&                   Key       => $key
\&              );
\&
\&    my $verified = $dsa\->verify(
\&                   Message   => "foo bar",
\&                   Signature => $sig,
\&                   Key       => $key,
\&              );
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fICrypt::DSA\fR is an implementation of the \s-1DSA\s0 (Digital Signature
Algorithm) signature verification system. The implementation
itself is pure Perl, although the heavy-duty mathematics underneath
are provided by the \fIMath::Pari\fR library.
.PP
This package provides \s-1DSA\s0 signing, signature verification, and key
generation.
.SH "USAGE"
.IX Header "USAGE"
The \fICrypt::DSA\fR public interface is similar to that of
\&\fICrypt::RSA\fR. This was done intentionally.
.SS "Crypt::DSA\->new"
.IX Subsection "Crypt::DSA->new"
Constructs a new \fICrypt::DSA\fR object. At the moment this isn't
particularly useful in itself, other than being the object you
need to do much else in the system.
.PP
Returns the new object.
.ie n .SS "$key = $dsa\->keygen(%arg)"
.el .SS "\f(CW$key\fP = \f(CW$dsa\fP\->keygen(%arg)"
.IX Subsection "$key = $dsa->keygen(%arg)"
Generates a new set of \s-1DSA\s0 keys, including both the public and
private portions of the key.
.PP
\&\fI\f(CI%arg\fI\fR can contain:
.IP "\(bu" 4
Size
.Sp
The size in bits of the \fIp\fR value to generate. The \fIq\fR and
\&\fIg\fR values are always 160 bits each.
.Sp
This argument is mandatory.
.IP "\(bu" 4
Seed
.Sp
A seed with which \fIq\fR generation will begin. If this seed does
not lead to a suitable prime, it will be discarded, and a new
random seed chosen in its place, until a suitable prime can be
found.
.Sp
This is entirely optional, and if not provided a random seed will
be generated automatically.
.IP "\(bu" 4
Verbosity
.Sp
Should be either 0 or 1. A value of 1 will give you a progress
meter during \fIp\fR and \fIq\fR generation\*(--this can be useful, since
the process can be relatively long.
.Sp
The default is 0.
.ie n .SS "$signature = $dsa\->sign(%arg)"
.el .SS "\f(CW$signature\fP = \f(CW$dsa\fP\->sign(%arg)"
.IX Subsection "$signature = $dsa->sign(%arg)"
Signs a message (or the digest of a message) using the private
portion of the \s-1DSA\s0 key and returns the signature.
.PP
The return value\*(--the signature\*(--is a \fICrypt::DSA::Signature\fR
object.
.PP
\&\fI\f(CI%arg\fI\fR can include:
.IP "\(bu" 4
Digest
.Sp
A digest to be signed. The digest should be 20 bytes in length
or less.
.Sp
You must provide either this argument or \fIMessage\fR (see below).
.IP "\(bu" 4
Key
.Sp
The \fICrypt::DSA::Key\fR object with which the signature will be
generated. Should contain a private key attribute (\fIpriv_key\fR).
.Sp
This argument is required.
.IP "\(bu" 4
Message
.Sp
A plaintext message to be signed. If you provide this argument,
\&\fIsign\fR will first produce a \s-1SHA1\s0 digest of the plaintext, then
use that as the digest to sign. Thus writing
.Sp
.Vb 1
\&    my $sign = $dsa\->sign(Message => $message, ... );
.Ve
.Sp
is a shorter way of writing
.Sp
.Vb 2
\&    use Digest::SHA qw( sha1 );
\&    my $sig = $dsa\->sign(Digest => sha1( $message ), ... );
.Ve
.ie n .SS "$verified = $dsa\->verify(%arg)"
.el .SS "\f(CW$verified\fP = \f(CW$dsa\fP\->verify(%arg)"
.IX Subsection "$verified = $dsa->verify(%arg)"
Verifies a signature generated with \fIsign\fR. Returns a true
value on success and false on failure.
.PP
\&\fI\f(CI%arg\fI\fR can contain:
.IP "\(bu" 4
Key
.Sp
Key of the signer of the message; a \fICrypt::DSA::Key\fR object.
The public portion of the key is used to verify the signature.
.Sp
This argument is required.
.IP "\(bu" 4
Signature
.Sp
The signature itself. Should be in the same format as returned
from \fIsign\fR, a \fICrypt::DSA::Signature\fR object.
.Sp
This argument is required.
.IP "\(bu" 4
Digest
.Sp
The original signed digest whose length is less than or equal to
20 bytes.
.Sp
Either this argument or \fIMessage\fR (see below) must be present.
.IP "\(bu" 4
Message
.Sp
As above in \fIsign\fR, the plaintext message that was signed, a
string of arbitrary length. A \s-1SHA1\s0 digest of this message will
be created and used in the verification process.
.SH "TODO"
.IX Header "TODO"
Add ability to munge format of keys. For example, read/write keys
from/to key files (\s-1SSH\s0 key files, etc.), and also write them in
other formats.
.SH "SUPPORT"
.IX Header "SUPPORT"
Bugs should be reported via the \s-1CPAN\s0 bug tracker at
.PP
<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Crypt\-DSA>
.PP
For other issues, contact the author.
.SH "AUTHOR"
.IX Header "AUTHOR"
Benjamin Trott <ben@sixapart.com>
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Except where otherwise noted,
Crypt::DSA is Copyright 2006 \- 2011 Benjamin Trott.
.PP
Crypt::DSA is free software; you may redistribute it
and/or modify it under the same terms as Perl itself.