Crypt::DH(3) User Contributed Perl Documentation Crypt::DH(3)NAMECrypt::DH - Diffie-Hellman key exchange system
SYNOPSIS
use Crypt::DH;
my $dh = Crypt::DH->new;
$dh->g($g);
$dh->p($p);
## Generate public and private keys.
$dh->generate_keys;
$my_pub_key = $dh->pub_key;
## Send $my_pub_key to "other" party, and receive "other"
## public key in return.
## Now compute shared secret from "other" public key.
my $shared_secret = $dh->compute_secret( $other_pub_key );
DESCRIPTIONCrypt::DH is a Perl implementation of the Diffie-Hellman key exchange
system. Diffie-Hellman is an algorithm by which two parties can agree
on a shared secret key, known only to them. The secret is negotiated
over an insecure network without the two parties ever passing the
actual shared secret, or their private keys, between them.
THE ALGORITHM
The algorithm generally works as follows: Party A and Party B choose a
property p and a property g; these properties are shared by both par-
ties. Each party then computes a random private key integer priv_key,
where the length of priv_key is at most (number of bits in p) - 1. Each
party then computes a public key based on g, priv_key, and p; the exact
value is
g ^ priv_key mod p
The parties exchange these public keys.
The shared secret key is generated based on the exchanged public key,
the private key, and p. If the public key of Party B is denoted
pub_key_B, then the shared secret is equal to
pub_key_B ^ priv_key mod p
The mathematical principles involved insure that both parties will gen-
erate the same shared secret key.
More information can be found in PKCS #3 (Diffie-Hellman Key Agreement
Standard):
http://www.rsasecurity.com/rsalabs/pkcs/pkcs-3/
USAGECrypt::DH implements the core routines needed to use Diffie-Hellman key
exchange. To actually use the algorithm, you'll need to start with val-
ues for p and g; p is a large prime, and g is a base which must be
larger than 0 and less than p.
Crypt::DH uses Math::BigInt internally for big-integer calculations.
All accessor methods (p, g, priv_key, and pub_key) thus return
Math::BigInt objects, as does the compute_secret method. The acces-
sors, however, allow setting with a scalar decimal string, hex string
(^0x), Math::BigInt object, or Math::Pari object (for backwards compat-
ibility).
$dh = Crypt::DH->new([ %param ]).
Constructs a new Crypt::DH object and returns the object. %param may
include none, some, or all of the keys p, g, and priv_key.
$dh->p([ $p ])
Given an argument $p, sets the p parameter (large prime) for this
Crypt::DH object.
Returns the current value of p. (as a Math::BigInt object)
$dh->g([ $g ])
Given an argument $g, sets the g parameter (base) for this Crypt::DH
object.
Returns the current value of g.
$dh->generate_keys
Generates the public and private key portions of the Crypt::DH object,
assuming that you've already filled p and g with appropriate values.
If you've provided a priv_key, it's used, otherwise a random priv_key
is created using either Crypt::Random (if already loaded), or
/dev/urandom, or Perl's rand, in that order.
$dh->compute_secret( $public_key )
Given the public key $public_key of Party B (the party with which
you're performing key negotiation and exchange), computes the shared
secret key, based on that public key, your own private key, and your
own large prime value (p).
The historical method name "compute_key" is aliased to this for compat-
ibility.
$dh->priv_key([ $priv_key ])
Returns the private key. Given an argument $priv_key, sets the
priv_key parameter for this Crypt::DH object.
$dh->pub_key
Returns the public key.
AUTHOR & COPYRIGHT
Benjamin Trott, ben@rhumba.pair.com
Brad Fitzpatrick, brad@danga.com
Except where otherwise noted, Crypt::DH is Copyright 2001 Benjamin
Trott. All rights reserved. Crypt::DH is free software; you may redis-
tribute it and/or modify it under the same terms as Perl itself.
perl v5.8.8 2005-06-11 Crypt::DH(3)
