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Crypt-Sodium-XS-0.000022
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/ Crypt::Sodium::XS::OO::scalarmult

NAME

Crypt::Sodium::XS::OO::scalarmult - Point-scalar multiplication over the edwards25519 curve

SYNOPSIS

use Crypt::Sodium::XS 'sodium_random_bytes';
my $scalarmult = Crypt::Sodium::XS->scalarmult;

my $keysize = Crypt::Sodium::XS->box->SECRETKEYBYTES;
my $client_sk = sodium_random_bytes($keysize);
my $client_pk = $scalarmult->base($client_sk);
my $server_sk = sodium_random_bytes($keysize);
my $server_pk = $scalarmult->base($client_sk);

# do not use output directly for key exchange. use Crypt::Sodium::XS::kx.
# a better shared key with scalarmult looks like:

# client side:
my $q = $scalarmult->scalarmult($client_sk, $server_pk);
my $hasher = Crypt::Sodium::XS->generichash->init;
$hasher->update($q, $client_pk, $server_pk);
my $client_shared_secret = $hasher->final;

# server side:
my $q = $scalarmult->scalarmult($server_sk, $client_pk);
my $hasher = Crypt::Sodium::XS->generichash->init;
$hasher->update($q, $client_pk, $server_pk);
my $server_shared_secret = $hasher->final;

# $client_shared_secret and $server_shared_secret are now identical keys.

DESCRIPTION

Crypt::Sodium::XS::scalarmult provides an API to multiply a point on the edwards25519 curve.

This can be used as a building block to construct key exchange mechanisms, or more generally to compute a public key from a secret key. For key exchange, you generally want to use Crypt::Sodium::XS::kx instead.

CONSTRUCTOR

new

my $scalarmult = Crypt::Sodium::XS::OO::scalarmult->new;
my $pwhash = Crypt::Sodium::XS->scalarmult;

Returns a new scalarmult object.

METHODS

BYTES

my $out_size = $scalarmult->BYTES

SCALARBYTES

my $out_size = $scalarmult->SCALARBYTES

keygen

my $secret_key = $scalarmult->keygen;

base

my $public_key = $scalarmult->base($secret_key);

scalarmult

my $q = $scalarmult->scalarmult($my_secret_key, $their_public_key);

Computes a shared secret q given a user’s secret key and another user’s public key.

$my_secret_key is "SCALARBYTES" bytes long, $their_public_key and the output are "BYTES" bytes long.

$q represents the X coordinate of a point on the curve. As a result, the number of possible keys is limited to the group size (≈2^252), which is smaller than the key space. For this reason, and to mitigate subtle attacks due to the fact many (p, n) pairs produce the same result, using the output of the multiplication q directly as a shared key is not recommended. See the "SYNOPSIS".

SEE ALSO

Crypt::Sodium::XS
Crypt::Sodium::XS::scalarmult
https://doc.libsodium.org/advanced/scalar_multiplication

FEEDBACK

For reporting bugs, giving feedback, submitting patches, etc. please use the following:

  • IRC channel #sodium on irc.perl.org.

  • Email the author directly.

For any security sensitive reports, please email the author directly or contact privately via IRC.

AUTHOR

Brad Barden <perlmodules@5c30.org>

COPYRIGHT & LICENSE

Copyright (c) 2022 Brad Barden. All rights reserved.

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