/ 
Crypt-Sodium-XS-0.000039
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/ Crypt::Sodium::XS::OO::auth

NAME

Crypt::Sodium::XS::OO::auth - Secret key message authentication

SYNOPSIS

use Crypt::Sodium::XS;

my $auth = Crypt::Sodium::XS->auth;

my $key = $auth->keygen;
my $msg = "authenticate this message";

my $tag = $auth->auth($msg, $key);
die "message tampered with!" unless $auth->verify($tag, $msg, $key);

my $multipart = $auth->init($key);
$multipart->update("authenticate");
$multipart->update(" this", " message");
$tag = $multipart->final;
die "message tampered with!" unless $auth->verify($tag, $msg, $key);

DESCRIPTION

Crypt::Sodium::XS::OO::auth computes an authentication tag for a message and a secret key, and provides a way to verify that a given tag is valid for a given message and a key.

The function computing the tag is deterministic: the same ($message, $key) tuple will always produce the same output. However, even if the message is public, knowing the key is required in order to be able to compute a valid tag. Therefore, the key should remain confidential. The tag, however, can be public.

A typical use case is:

* Alice prepares a message, adds an authentication tag, sends it to Bob

* Alice doesn't store the message

* Later on, Bob sends the message and the authentication tag back to Alice

* Alice uses the authentication tag to verify that she created this message

Crypt::Sodium::XS::OO::auth does not encrypt the message. It only computes and verifies an authentication tag.

CONSTRUCTOR

new

my $auth = Crypt::Sodium::XS::OO::auth->new(primitive => 'hmacsha256');
my $auth = Crypt::Sodium::XS->auth;

Returns a new auth object for the given primitive. If not given, the default primitive is default.

ATTRIBUTES

primitive

my $primitive = $auth->primitive;
$auth->primitive('hmacsha256');

Gets or sets the primitive used for all operations by this object. Note this can be default.

METHODS

primitives

my @primitives = Crypt::Sodium::XS::OO::auth->primitives;
my @primitives = $auth->primitives;

Returns a list of all supported primitive names, including default.

Can be called as a class method.

PRIMITIVE

my $primitive = $auth->PRIMITIVE;

Returns the primitive used for all operations by this object. Note this will never be default but would instead be the primitive it represents.

auth

my $tag = $auth->auth($message, $key);

$message is the message to authenticate. It may be a Crypt::Sodium::XS::MemVault.

$key is the secret key with which to generate the authentication tag. It must be "KEYBYTES" bytes. It may be a Crypt::Sodium::XS::MemVault.

Returns the authentication tag. The tag is "BYTES" bytes.

init

my $multipart = $auth->init($key, $flags);

$key is the secret key used by the multipart object. It should be at least "KEYBYTES" bytes. It may be a Crypt::Sodium::XS::MemVault.

$flags is optional. It is the flags used for the multipart protected memory object. See Crypt::Sodium::XS::ProtMem.

Returns an opaque protected memory object: a multi-part auth object. This is useful when authenticating a stream or large message in chunks, rather than in one message. See "MULTI-PART INTERFACE".

Note: The multipart interface may use arbitrary-size keys. This is not recommended as it can be easily misused (e.g., accidentally using an empty key). Avoid by always using keys of "KEYBYTES" bytes as returned by "keygen".

keygen

my $key = $auth->keygen($flags);

$flags is optional. It is the flags used for the $key Crypt::Sodium::XS::MemVault. See Crypt::Sodium::XS::ProtMem.

Returns a Crypt::Sodium::XS::MemVault: a new secret key of "KEYBYTES" bytes.

verify

my $is_valid = $auth->verify($tag, $message, $key);

$tag is the previously generated authentication tag. It must be "BYTES" bytes.

$message is the message to authenticate.

$key is the secret key used to generate the authentication tag. It must be "KEYBYTES" bytes. It may be a Crypt::Sodium::XS::MemVault.

Returns true if $tag is a valid tag for $message and $key, false otherwise.

BYTES

my $tag_size = $auth->BYTES;

The size, in bytes, of an authentication tag.

KEYBYTES

my $key_size = $auth->KEYBYTES;

The size, in bytes, of a secret key.

MULTI-PART INTERFACE

A multipart auth object is created by calling the "init" method. Data to be authenticated is added by calling the "update" method of that object as many times as desired. An output tag is generated by calling its "final" method. Do not use the object after calling "final".

The multipart auth object is an opaque object which provides the following methods:

clone

my $multipart_copy = $multipart->clone;

Returns a cloned copy of the multipart auth object, duplicating its internal state.

final

my $tag = $multipart->final;

Returns a tag for $key (from "init") and all authenticated data (from "update"). The tag is "BYTES" bytes.

Once "final" has been called, the multipart object must not be used further.

update

$multipart->update(@messages);

Adds all given arguments (stringified) to authenticated data. Any argument may be a Crypt::Sodium::XS::MemVault.

SEE ALSO

Crypt::Sodium::XS
Crypt::Sodium::XS::auth
https://doc.libsodium.org/secret-key_cryptography/secret-key_authentication
https://doc.libsodium.org/advanced/hmac-sha2

FEEDBACK

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

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.