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 plainMath::BigInt
, but if you want to use it in production, you almost always need to installMath::BigInt::GMP
orMath::BigInt::Pari
because without them, the computation that is required byCrypt::DH
makes the module pretty much unusable.Because of this,
Crypt::DH
might as well makeMath::BigInt::GMP
a hard requirement.  Crypt::DH suffers from having Math::BigInt in between GMP

With or without
Math::BigInt::GMP
orMath::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 bytepadded two's compliment in binary form.
pub_key_twoc
Returns the pub_key as a string that is bytepadded 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