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JSON Object Signing and Encryption (JOSE) for Erlang and Elixir.

Security advisory: This version has known vulnerabilities. View advisories
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jose src jose_chacha20_poly1305_crypto.erl
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src/jose_chacha20_poly1305_crypto.erl 

%% -*- mode: erlang; tab-width: 4; indent-tabs-mode: 1; st-rulers: [70] -*-

%% vim: ts=4 sw=4 ft=erlang noet

%%%-------------------------------------------------------------------

%%% @author Andrew Bennett <potatosaladx@gmail.com>

%%% @copyright 2014-2019, Andrew Bennett

%%% @doc

%%%

%%% @end

%%% Created :  08 Aug 2016 by Andrew Bennett <potatosaladx@gmail.com>

%%%-------------------------------------------------------------------

-module(jose_chacha20_poly1305_crypto).



-behaviour(jose_chacha20_poly1305).



%% jose_chacha20_poly1305 callbacks

-export([decrypt/5]).

-export([encrypt/4]).

-export([authenticate/3]).

-export([verify/4]).



%%====================================================================

%% jose_chacha20_poly1305 callbacks

%%====================================================================



decrypt(CipherText, CipherTag, AAD, IV, CEK) ->

	%% NOTE: As of OTP 22, crypto does not seem to validate the CipherTag :-(

	MacData = <<

		AAD/binary,

		(jose_jwa_chacha20_poly1305:pad16(AAD))/binary,

		CipherText/binary,

		(jose_jwa_chacha20_poly1305:pad16(CipherText))/binary,

		(byte_size(AAD)):64/unsigned-little-integer-unit:1,

		(byte_size(CipherText)):64/unsigned-little-integer-unit:1

	>>,

	case verify(CipherTag, MacData, CEK, IV) of

		true ->

			crypto:crypto_one_time_aead(chacha20_poly1305, CEK, IV, CipherText, AAD, CipherTag, false);

		false ->

			error

	end.



encrypt(PlainText, AAD, IV, CEK) ->

	crypto:crypto_one_time_aead(chacha20_poly1305, CEK, IV, PlainText, AAD, true).



authenticate(Message, Key, Nonce) ->

	OTK = jose_jwa_chacha20_poly1305:poly1305_key_gen(Key, Nonce),

	jose_crypto_compat:mac(poly1305, OTK, Message).



verify(MAC, Message, Key, Nonce) ->

	Challenge = jose_jwa_chacha20_poly1305:authenticate(Message, Key, Nonce),

	jose_jwa:constant_time_compare(MAC, Challenge).



%%%-------------------------------------------------------------------

%%% Internal functions

%%%-------------------------------------------------------------------