<html><head><meta name="color-scheme" content="light dark"></head><body><pre style="word-wrap: break-word; white-space: pre-wrap;">NAME
====

Crypt::Curve25519 - Generate shared secret using elliptic-curve Diffie-Hellman
function

VERSION
-------

version 0.07

SYNOPSIS
--------

        use Crypt::Curve25519;

        # Alice:
        my $alice_secret_key = curve25519_secret_key(random_32_bytes());
        my $alice_public_key = curve25519_public_key( $alice_secret_key );

        # Bob:
        my $bob_secret_key = curve25519_secret_key(random_32_bytes());
        my $bob_public_key = curve25519_public_key( $bob_secret_key );

        # Alice and Bob exchange their public keys
        my $alice_public_key_hex = unpack('H64', $alice_public_key);
        my $bob_public_key_hex   = unpack('H64', $bob_public_key);

        # Alice calculates shared secret to communicate with Bob
        my $shared_secret_with_bob = curve25519_shared_secret(
            $alice_secret_key,
            pack('H64', $bob_public_key_hex)
        );

        # Bob calculates shared secret to communicate with Alice
        my $shared_secret_with_alice = curve25519_shared_secret(
            $bob_secret_key,
            pack('H64', $alice_public_key_hex)
        );

        # Shared secrets are equal
        die "Something horrible has happend!"
          unless $shared_secret_with_bob eq $shared_secret_with_alice;

This package provides also simplified OO interface:

        use Crypt::Curve25519 ();

        my $c = Crypt::Curve25519-&gt;new();

        # Alice:
        my $alice_secret_key_hex = $c-&gt;secret_key(random_hexencoded_32_bytes());
        my $alice_public_key_hex = $c-&gt;public_key( $alice_secret_key_hex );

        # Bob:
        my $bob_secret_key_hex = $c-&gt;secret_key(random_hexencoded_32_bytes());
        my $bob_public_key_hex = $c-&gt;public_key( $bob_secret_key_hex );

        # Alice and Bob exchange their public keys

        # Alice calculates shared secret to communicate with Bob
        my $shared_secret_with_bob_hex = $c-&gt;shared_secret(
                                        $alice_secret_key_hex,
                                        $bob_public_key_hex);

        # Bob calculates shared secret to communicate with Alice
        my $shared_secret_with_alice_hex = $c-&gt;shared_secret(
                                        $bob_secret_key_hex,
                                        $alice_public_key_hex);

        # Shared secrets are equal
        die "Something horrible has happend!"
          unless $shared_secret_with_bob_hex eq $shared_secret_with_alice_hex;

Example functions to generate pseudo-random private secret key:

        sub random_32_bytes {
            return join('', map { chr(int(rand(255))) } 1 .. 32);
        }

        sub random_hexencoded_32_bytes {
           return unpack('H64', random_32_bytes());
        }

DESCRIPTION
-----------

Curve25519 is a state-of-the-art Diffie-Hellman function suitable for a wide
variety of applications.

Given a user's 32-byte secret key, Curve25519 computes the user's 32-byte
public key. Given the user's 32-byte secret key and another user's 32-byte
public key, Curve25519 computes a 32-byte secret shared by the two users. This
secret can then be used to authenticate and encrypt messages between the two
users.

METHODS
-------

### new
        my $c = Crypt::Curve25519-&gt;new();

Create a new object

### secret\_key
        my $my_secret_key_hex = $c-&gt;secret_key( $my_random_32byte_string_hex );

Using hex encoded 32-byte random string from cryptographically safe
source create masked secret key.

### public\_key
        my $public_key_hex = $c-&gt;public_key( $my_secret_key_hex );

Using hex encoded masked secret key generate corresponding hex encoded
32-byte Curve25519 public key.

### shared\_secret
        my $shared_secret_hex = $c-&gt;shared_secret(
            $my_secret_key_hex, $his_public_key_hex
        );

Using provided hex encoded keys generate 32-byte hex encoded shared
secret, that both parties can use without disclosing their private
secret keys.

### generate

Access to primitive method is also provided.

        my $key_hex = $c-&gt;generate($my_secret_key_hex, $basepoint_hex);

        # public key
        if ( $basepoint_hex eq unpack("H64", pack("H64", "09")) ) {
            print "\$key_hex is a public key\n";
        }
        elsif ( $basepoint_hex eq $his_public_key_hex ) {
            print "\$key_hex is a shared secret\n";
        }

Using provided hex encoded secret key and depending on the 32-byte hex
encoded basepoint generate 32-byte hex encoded public key or shared
secret.

FUNCTIONS
---------

### curve25519\_secret\_key

        my $my_secret_key = curve25519_secret_key($my_random_32byte_string);

Using provided 32-byte random string from cryptographically safe source
create masked secret key.

### curve25519\_public\_key

        my $public_key = curve25519_public_key($my_secret_key);

Using masked secret key generate corresponding 32-byte Curve25519 public
key.

### curve25519\_shared\_secret

        my $shared_secret = curve25519_shared_secret(
            $my_secret_key, $his_public_key
        );

Using provided keys generate 32-byte shared secret, that both parties
can use without disclosing their private secret keys.

### curve25519

Access to primitive function is also provided.

        use Crypt::Curve25519 'curve25519';

        my $key = curve25519($my_secret_key, $basepoint);

        # public key
        if ( $basepoint eq pack('H64', '09') ) {
            print "\$key is a public key\n";
        }
        elsif ( $basepoint eq $his_public_key ) {
            print "\$key is a shared secret\n";
        }

Using provided secret key and depending on the 32-byte basepoint
generate 32-byte public key or shared secret.

SEE ALSO
--------
    http://cr.yp.to/ecdh.html

AUTHOR
------

    Alex J. G. BurzyĹ„ski &lt;ajgb@cpan.org&gt;

MAINTAINER
----------

    Dmitry Karasik &lt;dmitry@karasik.eu.org&gt;

COPYRIGHT AND LICENSE
---------------------

This software is copyright (c) 2014 by Alex J. G. BurzyĹ„ski &lt;ajgb@cpan.org&gt;.

This is free software; you can redistribute it and/or modify it under the same
terms as the Perl 5 programming language system itself.

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