NAME

       Crypt::DH::GMP - Crypt::DH Using GMP Directly

SYNOPSIS

         use Crypt::DH::GMP;

         my $dh = Crypt::DH::GMP->new(p => $p, g => $g);
         my $val = $dh->compute_secret();

         # If you want compatibility with Crypt::DH (it uses Math::BigInt)
         # then use this flag
         # You /think/ you're using Crypt::DH, but...
         use Crypt::DH::GMP qw(-compat);

         my $dh = Crypt::DH->new(p => $p, g => $g);
         my $val = $dh->compute_secret();

DESCRIPTION

       Crypt::DH::GMP is a (somewhat) portable replacement to Crypt::DH, implemented mostly in C.

RATIONALE

       In the beginning, there was "Crypt::DH". However, "Crypt::DH" suffers from a couple of
       problems:

       GMP/Pari libraries are almost always required
           "Crypt::DH" works with a plain "Math::BigInt", but if you want to use it in
           production, you almost always need to install "Math::BigInt::GMP" or
           "Math::BigInt::Pari" because without them, the computation that is required by
           "Crypt::DH" makes the module pretty much unusable.

           Because of this, "Crypt::DH" might as well make "Math::BigInt::GMP" a hard
           requirement.

       Crypt::DH suffers from having Math::BigInt in between GMP
           With or without "Math::BigInt::GMP" or "Math::BigInt::Pari", "Crypt::DH" makes several
           round trip conversions between Perl scalars, Math::BigInt objects, and finally its C
           representation (if GMP/Pari are installed).

           Instantiating an object comes with a relatively high cost, and if you make many
           computations in one go, your program will suffer dramatically because of this.

       These problems quickly become apparent when you use modules such as
       "Net::OpenID::Consumer", which requires to make a few calls to "Crypt::DH".

       "Crypt::DH::GMP" attempts to alleviate these problems by providing a
       "Crypt::DH"-compatible layer, which, instead of doing calculations via Math::BigInt,
       directly works with libgmp in C.

       This means that we've essentially eliminated 2 call stacks worth of expensive Perl method
       calls and we also only load 1 (Crypt::DH::GMP) module instead of 3 (Crypt::DH +
       Math::BigInt + Math::BigInt::GMP).

       These add up to a fairly significant increase in performance.

COMPATIBILITY WITH Crypt::DH

       Crypt::DH::GMP absolutely refuses to consider using anything other than strings as its
       parameters and/or return values therefore if you would like to use Math::BigInt objects as
       your return values, you can not use Crypt::DH::GMP directly. Instead, you need to be
       explicit about it:

         use Crypt::DH;
         use Crypt::DH::GMP qw(-compat); # must be loaded AFTER Crypt::DH

       Specifying -compat invokes a very nasty hack that overwrites Crypt::DH's symbol table --
       this then forces Crypt::DH users to use Crypt::DH::GMP instead, even if you are writing

         my $dh = Crypt::DH->new(...);
         $dh->compute_key();

BENCHMARK

       By NO MEANS is this an exhaustive benchmark, but here's what I get on my MacBook (OS X
       10.5.8, 2.4 GHz Core 2 Duo, 4GB RAM)

         Benchmarking instatiation cost...
                Rate   pp  gmp
         pp   9488/s   -- -79%
         gmp 45455/s 379%   --

         Benchmarking key generation cost...
               Rate gmp  pp
         gmp 6.46/s  -- -0%
         pp  6.46/s  0%  --

         Benchmarking compute_key cost...
                 Rate    pp   gmp
         pp   12925/s    --  -96%
         gmp 365854/s 2730%    --

METHODS

   new
   p
   g
   compute_key
   compute_secret
   generate_keys
   pub_key
   priv_key
   compute_key_twoc
       Computes the key, and returns a string that is byte-padded two's compliment in binary
       form.

   pub_key_twoc
       Returns the pub_key as a string that is byte-padded two's compliment in binary form.

   clone

AUTHOR

       Daisuke Maki "<daisuke@endeworks.jp>"

LICENSE

       This program is free software; you can redistribute it and/or modify it under the same
       terms as Perl itself.

       See http://www.perl.com/perl/misc/Artistic.html