

 
Manual Reference Pages  CRYPT::DH (3)
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NAME
Crypt::DH  DiffieHellman key exchange system
CONTENTS
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( $other_pub_key );
DESCRIPTION
Crypt::DH is a Perl implementation of the DiffieHellman key
exchange system. DiffieHellman is an algorithm by which two
parties can agree on a shared secret key, known only to them.
The secret is negotiated over an insecure network without the
two parties ever passing the actual shared secret, or their
private keys, between them.
THE ALGORITHM
The algorithm generally works as follows: Party A and Party B
choose a property p and a property g; these properties are
shared by both parties. Each party then computes a random private
key integer priv_key, where the length of priv_key is at
most (number of bits in p)  1. Each party then computes a
public key based on g, priv_key, and p; the exact value
is
g ^ priv_key mod p
The parties exchange these public keys.
The shared secret key is generated based on the exchanged public
key, the private key, and p. If the public key of Party B is
denoted pub_key_B, then the shared secret is equal to
pub_key_B ^ priv_key mod p
The mathematical principles involved insure that both parties will
generate the same shared secret key.
More information can be found in PKCS #3 (DiffieHellman Key
Agreement Standard):
http://www.rsasecurity.com/rsalabs/pkcs/pkcs3/
USAGE
Crypt::DH implements the core routines needed to use
DiffieHellman key exchange. To actually use the algorithm,
you’ll need to start with values for p and g; p is a
large prime, and g is a base which must be larger than 0
and less than p.
Crypt::DH uses Math::BigInt internally for biginteger
calculations. All accessor methods (p, g, priv_key, and
pub_key) thus return Math::BigInt objects, as does the
compute_secret method. The accessors, however, allow setting with a
scalar decimal string, hex string (^0x), Math::BigInt object, or
Math::Pari object (for backwards compatibility).
Constructs a new Crypt::DH object and returns the object.
%param may include none, some, or all of the keys p, g, and
priv_key.
CW$dh>p([ CW$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)
Given an argument $g, sets the g parameter (base) for
this Crypt::DH object.
Returns the current value of g.
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.
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
compatibility.
Returns the private key. Given an argument $priv_key, sets the
priv_key parameter for this Crypt::DH object.
CW$dh>pub_key
Returns the public key.
AUTHOR
Benjamin Trott (cpan:BTROTT) <ben+cpan@stupidfool.org>
Brad Fitzpatrick (cpan:BRADFITZ) <brad@danga.com>
CONTRIBUTORS
BinGOs  Chris Williams (cpan:BINGOS) <chris@bingosnet.co.uk>
Mithaldu  Christian Walde (cpan:MITHALDU) <walde.christian@googlemail.com>
COPYRIGHT
Copyright (c) 2012 the Crypt::DH AUTHOR and CONTRIBUTORS as listed
above.
LICENSE
This library is free software and may be distributed under the same terms
as perl itself.
perl v5.20.3  CRYPT::DH (3)  20120706 
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