# phpman > man > Crypt::DH::GMP(3pm) ## NAME [Crypt::DH::GMP](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH%3A%3AGMP/markdown) - [Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown) Using GMP Directly ## SYNOPSIS use [Crypt::DH::GMP](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH%3A%3AGMP/markdown); my $dh = [Crypt::DH::GMP](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH%3A%3AGMP/markdown)->new(p => $p, g => $g); my $val = $dh->compute_secret(); # If you want compatibility with [Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown) (it uses [Math::BigInt](https://www.chedong.com/phpMan.php/perldoc/Math%3A%3ABigInt/markdown)) # then use this flag # You /think/ you're using [Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown), but... use [Crypt::DH::GMP](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH%3A%3AGMP/markdown) qw(-compat); my $dh = [Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown)->new(p => $p, g => $g); my $val = $dh->compute_secret(); ## DESCRIPTION [Crypt::DH::GMP](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH%3A%3AGMP/markdown) is a (somewhat) portable replacement to [Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown), implemented mostly in C. ## RATIONALE In the beginning, there was "[Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown)". However, "[Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown)" suffers from a couple of problems: GMP/Pari libraries are almost always required "[Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown)" works with a plain "[Math::BigInt](https://www.chedong.com/phpMan.php/perldoc/Math%3A%3ABigInt/markdown)", but if you want to use it in production, you almost always need to install "[Math::BigInt::GMP](https://www.chedong.com/phpMan.php/perldoc/Math%3A%3ABigInt%3A%3AGMP/markdown)" or "[Math::BigInt::Pari](https://www.chedong.com/phpMan.php/perldoc/Math%3A%3ABigInt%3A%3APari/markdown)" because without them, the computation that is required by "[Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown)" makes the module pretty much unusable. Because of this, "[Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown)" might as well make "[Math::BigInt::GMP](https://www.chedong.com/phpMan.php/perldoc/Math%3A%3ABigInt%3A%3AGMP/markdown)" a hard requirement. [Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown) suffers from having [Math::BigInt](https://www.chedong.com/phpMan.php/perldoc/Math%3A%3ABigInt/markdown) in between GMP With or without "[Math::BigInt::GMP](https://www.chedong.com/phpMan.php/perldoc/Math%3A%3ABigInt%3A%3AGMP/markdown)" or "[Math::BigInt::Pari](https://www.chedong.com/phpMan.php/perldoc/Math%3A%3ABigInt%3A%3APari/markdown)", "[Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown)" makes several round trip conversions between Perl scalars, [Math::BigInt](https://www.chedong.com/phpMan.php/perldoc/Math%3A%3ABigInt/markdown) 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](https://www.chedong.com/phpMan.php/perldoc/Net%3A%3AOpenID%3A%3AConsumer/markdown)", which requires to make a few calls to "[Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown)". "[Crypt::DH::GMP](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH%3A%3AGMP/markdown)" attempts to alleviate these problems by providing a "[Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown)"-compatible layer, which, instead of doing calculations via [Math::BigInt](https://www.chedong.com/phpMan.php/perldoc/Math%3A%3ABigInt/markdown), 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](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH%3A%3AGMP/markdown)) module instead of 3 ([Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown) + [Math::BigInt](https://www.chedong.com/phpMan.php/perldoc/Math%3A%3ABigInt/markdown) + [Math::BigInt::GMP](https://www.chedong.com/phpMan.php/perldoc/Math%3A%3ABigInt%3A%3AGMP/markdown)). These add up to a fairly significant increase in performance. COMPATIBILITY WITH [Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown) [Crypt::DH::GMP](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH%3A%3AGMP/markdown) 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](https://www.chedong.com/phpMan.php/perldoc/Math%3A%3ABigInt/markdown) objects as your return values, you can not use [Crypt::DH::GMP](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH%3A%3AGMP/markdown) directly. Instead, you need to be explicit about it: use [Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown); use [Crypt::DH::GMP](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH%3A%3AGMP/markdown) qw(-compat); # must be loaded AFTER [Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown) Specifying -compat invokes a very nasty hack that overwrites [Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown)'s symbol table -- this then forces [Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown) users to use [Crypt::DH::GMP](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH%3A%3AGMP/markdown) instead, even if you are writing my $dh = [Crypt::DH](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADH/markdown)->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 "<>" ## LICENSE This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See