From 5cfdbc49647b6be943d01e4ab141b705e9e5c86d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Roman=20Smr=C5=BE?= <roman.smrz@seznam.cz>
Date: Wed, 27 Jul 2022 22:01:50 +0200
Subject: Explicit identities in pairing request

Actual device identities can change at any point during the pairing
process, so it is necessary to fix the ones used for nonce confirmation
and just initially verify that they belong to the respective sides.
---
 include/erebos/pairing.h |  2 ++
 src/pairing.cpp          | 47 +++++++++++++++++++++++++++++++++++++----------
 2 files changed, 39 insertions(+), 10 deletions(-)

diff --git a/include/erebos/pairing.h b/include/erebos/pairing.h
index 936b3ac..ea349a9 100644
--- a/include/erebos/pairing.h
+++ b/include/erebos/pairing.h
@@ -83,6 +83,8 @@ private:
 	struct State {
 		mutex lock;
 		StatePhase phase;
+		optional<Identity> idReq;
+		optional<Identity> idRsp;
 		vector<uint8_t> nonce;
 		vector<uint8_t> peerCheck;
 		promise<Outcome> outcome;
diff --git a/src/pairing.cpp b/src/pairing.cpp
index babe886..f25cb5c 100644
--- a/src/pairing.cpp
+++ b/src/pairing.cpp
@@ -74,6 +74,24 @@ void PairingServiceBase::handle(Context & ctx)
 	unique_lock lock_state(state->lock);
 
 	if (auto request = rec->item("request").asBinary()) {
+		auto idReqRef = rec->item("id-req").asRef();
+		if (!idReqRef)
+			return;
+		auto idReq = Identity::load(*idReqRef);
+		if (!idReq)
+			return;
+		if (!idReq->sameAs(*pid))
+			return;
+
+		auto idRspRef = rec->item("id-rsp").asRef();
+		if (!idRspRef)
+			return;
+		auto idRsp = Identity::load(*idRspRef);
+		if (!idRsp)
+			return;
+		if (!idRsp->sameAs(ctx.peer().server().identity()))
+			return;
+
 		if (state->phase >= StatePhase::PairingDone) {
 			auto nstate = make_shared<State>();
 			lock_state = unique_lock(nstate->lock);
@@ -85,6 +103,8 @@ void PairingServiceBase::handle(Context & ctx)
 			requestInitHook(ctx.peer());
 
 		state->phase = StatePhase::PeerRequest;
+		state->idReq = idReq;
+		state->idRsp = idRsp;
 		state->peerCheck = *request;
 		state->nonce.resize(32);
 		RAND_bytes(state->nonce.data(), state->nonce.size());
@@ -102,7 +122,7 @@ void PairingServiceBase::handle(Context & ctx)
 
 		if (responseHook) {
 			string confirm = confirmationNumber(nonceDigest(
-				ctx.peer().server().identity(), *pid, 
+				*state->idReq, *state->idRsp,
 				state->nonce, *response));
 			std::thread(&PairingServiceBase::waitForConfirmation,
 					this, ctx.peer(), state, confirm, responseHook).detach();
@@ -116,8 +136,11 @@ void PairingServiceBase::handle(Context & ctx)
 	}
 
 	else if (auto reqnonce = rec->item("reqnonce").asBinary()) {
+		if (state->phase != StatePhase::PeerRequest)
+			return;
+
 		auto check = nonceDigest(
-				*pid, ctx.peer().server().identity(),
+				*state->idReq, *state->idRsp,
 				*reqnonce, vector<uint8_t>());
 		if (check != state->peerCheck) {
 			if (requestNonceFailedHook)
@@ -131,7 +154,7 @@ void PairingServiceBase::handle(Context & ctx)
 
 		if (requestHook) {
 			string confirm = confirmationNumber(nonceDigest(
-				*pid, ctx.peer().server().identity(),
+				*state->idReq, *state->idRsp,
 				*reqnonce, state->nonce));
 			std::thread(&PairingServiceBase::waitForConfirmation,
 					this, ctx.peer(), state, confirm, requestHook).detach();
@@ -174,25 +197,29 @@ void PairingServiceBase::requestPairing(UUID serviceId, const Peer & peer)
 	}
 
 	state->phase = StatePhase::OurRequest;
+	state->idReq = peer.server().identity();
+	state->idRsp = pid;
 	state->nonce.resize(32);
 	RAND_bytes(state->nonce.data(), state->nonce.size());
 
 	vector<Record::Item> items;
+	items.emplace_back("id-req", state->idReq->ref().value());
+	items.emplace_back("id-rsp", state->idRsp->ref().value());
 	items.emplace_back("request", nonceDigest(
-				peer.server().identity(), *pid,
+				*state->idReq, *state->idRsp,
 				state->nonce, vector<uint8_t>()));
 
 	peer.send(serviceId, Object(Record(std::move(items))));
 }
 
-vector<uint8_t> PairingServiceBase::nonceDigest(const Identity & id1, const Identity & id2,
-	const vector<uint8_t> & nonce1, const vector<uint8_t> & nonce2)
+vector<uint8_t> PairingServiceBase::nonceDigest(const Identity & idReq, const Identity & idRsp,
+	const vector<uint8_t> & nonceReq, const vector<uint8_t> & nonceRsp)
 {
 	vector<Record::Item> items;
-	items.emplace_back("id", id1.ref().value());
-	items.emplace_back("id", id2.ref().value());
-	items.emplace_back("nonce", nonce1);
-	items.emplace_back("nonce", nonce2);
+	items.emplace_back("id-req", idReq.ref().value());
+	items.emplace_back("id-rsp", idRsp.ref().value());
+	items.emplace_back("nonce-req", nonceReq);
+	items.emplace_back("nonce-rsp", nonceRsp);
 
 	const auto arr = Digest::of(Object(Record(std::move(items)))).arr();
 	vector<uint8_t> ret(arr.size());
-- 
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