README
1NAME
2 Crypt::DH - Diffie-Hellman key exchange system
3
4SYNOPSIS
5 use Crypt::DH;
6 my $dh = Crypt::DH->new;
7 $dh->g($g);
8 $dh->p($p);
9
10 ## Generate public and private keys.
11 $dh->generate_keys;
12
13 $my_pub_key = $dh->pub_key;
14
15 ## Send $my_pub_key to "other" party, and receive "other"
16 ## public key in return.
17
18 ## Now compute shared secret from "other" public key.
19 my $shared_secret = $dh->compute_secret( $other_pub_key );
20
21DESCRIPTION
22 *Crypt::DH* is a Perl implementation of the Diffie-Hellman key exchange
23 system. Diffie-Hellman is an algorithm by which two parties can agree on
24 a shared secret key, known only to them. The secret is negotiated over
25 an insecure network without the two parties ever passing the actual
26 shared secret, or their private keys, between them.
27
28THE ALGORITHM
29 The algorithm generally works as follows: Party A and Party B choose a
30 property *p* and a property *g*; these properties are shared by both
31 parties. Each party then computes a random private key integer
32 *priv_key*, where the length of *priv_key* is at most (number of bits in
33 *p*) - 1. Each party then computes a public key based on *g*,
34 *priv_key*, and *p*; the exact value is
35
36 g ^ priv_key mod p
37
38 The parties exchange these public keys.
39
40 The shared secret key is generated based on the exchanged public key,
41 the private key, and *p*. If the public key of Party B is denoted
42 *pub_key_B*, then the shared secret is equal to
43
44 pub_key_B ^ priv_key mod p
45
46 The mathematical principles involved insure that both parties will
47 generate the same shared secret key.
48
49 More information can be found in PKCS #3 (Diffie-Hellman Key Agreement
50 Standard):
51
52 http://www.rsasecurity.com/rsalabs/pkcs/pkcs-3/
53
54USAGE
55 *Crypt::DH* implements the core routines needed to use Diffie-Hellman
56 key exchange. To actually use the algorithm, you'll need to start with
57 values for *p* and *g*; *p* is a large prime, and *g* is a base which
58 must be larger than 0 and less than *p*.
59
60 *Crypt::DH* uses *Math::BigInt* internally for big-integer calculations.
61 All accessor methods (*p*, *g*, *priv_key*, and *pub_key*) thus return
62 *Math::BigInt* objects, as does the *compute_secret* method. The
63 accessors, however, allow setting with a scalar decimal string, hex
64 string (^0x), Math::BigInt object, or Math::Pari object (for backwards
65 compatibility).
66
67 $dh = Crypt::DH->new([ %param ]).
68 Constructs a new *Crypt::DH* object and returns the object. *%param* may
69 include none, some, or all of the keys *p*, *g*, and *priv_key*.
70
71 $dh->p([ $p ])
72 Given an argument *$p*, sets the *p* parameter (large prime) for this
73 *Crypt::DH* object.
74
75 Returns the current value of *p*. (as a Math::BigInt object)
76
77 $dh->g([ $g ])
78 Given an argument *$g*, sets the *g* parameter (base) for this
79 *Crypt::DH* object.
80
81 Returns the current value of *g*.
82
83 $dh->generate_keys
84 Generates the public and private key portions of the *Crypt::DH* object,
85 assuming that you've already filled *p* and *g* with appropriate values.
86
87 If you've provided a priv_key, it's used, otherwise a random priv_key is
88 created using either Crypt::Random (if already loaded), or /dev/urandom,
89 or Perl's rand, in that order.
90
91 $dh->compute_secret( $public_key )
92 Given the public key *$public_key* of Party B (the party with which
93 you're performing key negotiation and exchange), computes the shared
94 secret key, based on that public key, your own private key, and your own
95 large prime value (*p*).
96
97 The historical method name "compute_key" is aliased to this for
98 compatibility.
99
100 $dh->priv_key([ $priv_key ])
101 Returns the private key. Given an argument *$priv_key*, sets the
102 *priv_key* parameter for this *Crypt::DH* object.
103
104 $dh->pub_key
105 Returns the public key.
106
107AUTHOR
108 Benjamin Trott (cpan:BTROTT) <ben+cpan@stupidfool.org>
109
110 Brad Fitzpatrick (cpan:BRADFITZ) <brad@danga.com>
111
112CONTRIBUTORS
113 BinGOs - Chris Williams (cpan:BINGOS) <chris@bingosnet.co.uk>
114
115 Mithaldu - Christian Walde (cpan:MITHALDU)
116 <walde.christian@googlemail.com>
117
118COPYRIGHT
119 Copyright (c) 2012 the Crypt::DH "AUTHOR" and "CONTRIBUTORS" as listed
120 above.
121
122LICENSE
123 This library is free software and may be distributed under the same
124 terms as perl itself.
125
126