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Manual Reference Pages  -  CRYPT::GCRYPT::MPI (3)

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NAME

Crypt::GCrypt::MPI - Perl interface to multi-precision integers from the GNU Cryptographic library

CONTENTS

SYNOPSIS



  use Crypt::GCrypt::MPI;

  my $mpi = Crypt::GCrypt::MPI->new();



ABSTRACT

Crypt::GCrypt::MPI provides an object interface to multi-precision integers from the C libgcrypt library.

BASIC OPERATIONS

new()

Create a new multi-precision integer.



  my $mpi = Crypt::GCrypt::MPI::new(
    secure => 1,
    value => 20,
  );



No parameters are required. If only one parameter is given, it is treated as the value parameter. Available parameters:
value The initial value of the MPI. This can be an integer, a string, or another Crypt::GCrypt::MPI. (It would also be nice to be able to initialize it with a Math::Int).
secure If this parameter evaluates to non-zero, initialize the MPI using secure memory, if possible.
format If the value is a string, the format parameter suggests how to convert the string. See CONVERSION FORMATS for the available formats. Defaults to Crypt::GCrypt::MPI::FMT_STD.

set()

Copies the value of the other Crypt::GCrypt::MPI object.



  $mpi->set($othermpi);



swap()

Exchanges the value with the value of another Crypt::GCrpyt::MPI object:



  $mpi->swap($othermpi);



is_secure()

Returns true if the Crypt::GCrypt::MPI uses secure memory, where possible.

    cmp($other)

Compares this object against another Crypt::GCrypt::MPI object, returning 0 if the two values are equal, positive if this value is greater, negative if $other is greater.

    mutually_prime($other)

Compares this object against another Crypt::GCrypt::MPI object, returning true only if the two values share no factors in common other than 1.

copy()

Returns a new Crypt::GCrypt::MPI object, with the contents identical to this one. This is different from using the assignment operator (=), which just makes two references to the same object. For example:



 $b = new Crypt::GCrypt::MPI(15);
 $a = $b;
 $b->add(1); # $a points to the same object,
             # so both $a and $b contain 16.

 $a = $b->copy(); # $a and $b are both 16, but
                  # different objects; no risk of
                  # double-free.
 $b->add(1); # $a == 16, $b == 17



If $b is a Crypt::GCrypt::MPI object, then $a = $b->copy(); is identical to $a = Crypt::GCrypt::MPI->new($b);

CALCULATIONS

All calculation operations modify the object they are called on, and return the same object, so you can chain them like this:



 $g->addm($a, $m)->mulm($b, $m)->gcd($x);



If you don’t want an operation to affect the initial object, use the copy() operator:



 $h = $g->copy()->addm($a, $m)->mulm($b, $m)->gcd($x);



    add($other)

Adds the value of $other to this MPI.

addm($other, CW$modulus)

Adds the value of $other to this MPI, modulo the value of $modulus.

    sub($other)

Subtracts the value of $other from this MPI.

subm($other, CW$modulus)

Subtracts the value of $other from this MPI, modulo the value of $modulus.

    mul($other)

Multiply this MPI by the value of $other.

mulm($other, CW$modulus)

Multiply this MPI by the value of $other, modulo the value of $modulus.

    mul_2exp($e)

Multiply this MPI by 2 raised to the power of $e (this is a leftward bitshift)

    div($other)

Divide this MPI by the value of $other, leaving the integer quotient. (This is integer division)

    mod($other)

Divide this MPI by the value of $other, leaving the integer remainder. (This is the modulus operation)

powm($other, CW$modulus)

Raise this MPI to the power of $other, modulo the value of $modulus.

    invm($modulus)

Find the multiplicative inverse of this MPI, modulo $modulus.

    gcd($other)

Find the greatest common divisor of this MPI and $other.

OUTPUT AND DEBUGGING

dump()

Send the MPI to the libgcrypt debugging stream.

    print($format)

Return a string with the data of this MPI, in a given format. See CONVERSION FORMATS for the available formats.

CONVERSION FORMATS

The available printing and scanning formats are all in the Crypt::GCrypt::MPI namespace, and have the same meanings as in gcrypt.

    FMT_STD

Two’s complement representation.

    FMT_PGP

Same as FMT_STD, but with two-byte length header, as used in OpenPGP. (Only works for non-negative values)

    FMT_SSH

Same as FMT_STD, but with four-byte length header, as used by OpenSSH.

    FMT_HEX

Hexadecimal string in ASCII.

    FMT_USG

Simple unsigned integer.

BUGS AND FEEDBACK

Crypt::GCrypt::MPI does not currently auto-convert to and from Math::BigInt objects, even though it should.

Other than that, here are no known bugs. You are very welcome to write mail to the maintainer (aar@cpan.org) with your contributions, comments, suggestions, bug reports or complaints.

AUTHORS AND CONTRIBUTORS

Daniel Kahn Gillmor <dkg@fifthhorseman.net>

Alessandro Ranellucci <aar@cpan.org>

COPYRIGHT AND LICENSE

Copyright X Daniel Kahn Gillmor. Crypt::GCrypt::MPI is free software, you may redistribute it and/or modify it under the same terms as Perl itself.

ACKNOWLEDGEMENTS

This module was initially inspired by the GCrypt.pm bindings made by Robert Bihlmeyer in 2002. Thanks to users who give feedback and submit patches (see Changelog).

DISCLAIMER

This software is provided by the copyright holders and contributors ‘‘as is’’ and any express or implied warranties, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose are disclaimed. In no event shall the regents or contributors be liable for any direct, indirect, incidental, special, exemplary, or consequential damages (including, but not limited to, procurement of substitute goods or services; loss of use, data, or profits; or business interruption) however caused and on any theory of liability, whether in contract, strict liability, or tort (including negligence or otherwise) arising in any way out of the use of this software, even if advised of the possibility of such damage.
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