--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mod_cloud_notify_encrypted/mod_cloud_notify_encrypted.lua	Tue Jan 12 15:43:26 2021 +0000
@@ -0,0 +1,100 @@
+local base64 = require "util.encodings".base64;
+local ciphers = require "openssl.cipher";
+local jid = require "util.jid";
+local json = require "util.json";
+local random = require "util.random";
+local st = require "util.stanza";
+
+local xmlns_jmi = "urn:xmpp:jingle-message:0";
+local xmlns_push = "urn:xmpp:push:0";
+local xmlns_push_encrypt = "tigase:push:encrypt:0";
+local xmlns_push_encrypt_aes_128_gcm = "tigase:push:encrypt:aes-128-gcm";
+
+-- https://xeps.tigase.net//docs/push-notifications/encrypt/#41-discovering-support
+local function account_disco_info(event)
+	event.reply:tag("feature", {var=xmlns_push_encrypt}):up();
+	event.reply:tag("feature", {var=xmlns_push_encrypt_aes_128_gcm}):up();
+end
+module:hook("account-disco-info", account_disco_info);
+
+function handle_register(event)
+	local encrypt = event.stanza:get_child("encrypt", xmlns_push_encrypt);
+	if not encrypt then return; end
+
+	local algorithm = encrypt.attr.alg;
+	if algorithm ~= "aes-128-gcm" then
+		event.origin.send(st.error_reply(
+			event.stanza, "modify", "feature-not-implemented", "Unknown encryption algorithm"
+		));
+		return false;
+	end
+
+	local key_base64 = encrypt:get_text();
+	local key_binary = base64.decode(key_base64);
+	if not key_binary or #key_binary ~= 16 then
+		event.origin.send(st.error_reply(
+			event.stanza, "modify", "bad-request", "Invalid encryption key"
+		));
+		return false;
+	end
+
+	event.push_info.encryption = {
+		algorithm = algorithm;
+		key_base64 = key_base64;
+	};
+end
+
+function handle_push(event)
+	local encryption = event.push_info.encryption;
+	if not encryption then return; end
+
+	if encryption.algorithm ~= "aes-128-gcm" then
+		event.reason = "Unsupported encryption algorithm: "..tostring(encryption.algorithm);
+		return true;
+	end
+
+	local push_summary = event.push_summary;
+
+	local original_stanza = event.original_stanza;
+
+	local push_payload = {
+		unread = push_summary["message-count"];
+		sender = push_summary["last-message-sender"];
+	};
+
+	if original_stanza.name == "message" then
+		if original_stanza.attr.type == "groupchat" then
+			push_payload.type = "groupchat";
+			push_payload.nickname = jid.resource(original_stanza.attr.from);
+		elseif original_stanza.attr.type ~= "error" then
+			local jmi_propose = original_stanza:get_child("propose", xmlns_jmi);
+			if jmi_propose then
+				push_payload.type = "call";
+				push_payload.sid = jmi_propose.attr.id;
+			else
+				push_payload.type = "chat";
+			end
+		end
+	elseif original_stanza.name == "presence"
+	and original_stanza.attr.type == "subscribe" then
+		push_payload.type = "subscribe";
+	end
+
+	local iv = random.bytes(12);
+	local key_binary = base64.decode(encryption.key_base64);
+	local push_json = json.encode(push_payload);
+
+	local encrypted_payload = ciphers.new("AES-128-GCM"):encrypt(key_binary, iv):final(push_json);
+	local encrypted_element = st.stanza("encrypted", { xmlns = xmlns_push_encrypt, iv = base64.encode(iv) })
+		:text(encrypted_payload);
+	-- Replace the unencrypted notification with the encrypted one
+	event.notification_stanza
+		:get_child("pubsub", "http://jabber.org/protocol/pubsub")
+		:get_child("publish")
+		:get_child("item")
+		:remove_children("notification", xmlns_push)
+		:add_child(encrypted_element);
+end
+
+module:hook("cloud_notify/registration", handle_register);
+module:hook("cloud_notify/push", handle_push);