diff --git a/src/activitypub/actors.js b/src/activitypub/actors.js
index baeba99c61..8fdbc543a5 100644
--- a/src/activitypub/actors.js
+++ b/src/activitypub/actors.js
@@ -31,6 +31,7 @@ Actors.assert = async (ids, options = {}) => {
 	winston.verbose(`[activitypub/actors] Asserting ${ids.length} actor(s)`);
 
 	const followersUrlMap = new Map();
+	const pubKeysMap = new Map();
 	const actors = await Promise.all(ids.map(async (id) => {
 		try {
 			winston.verbose(`[activitypub/actors] Processing ${id}`);
@@ -58,6 +59,9 @@ Actors.assert = async (ids, options = {}) => {
 				followersUrlMap.set(actor.followers, actor.id);
 			}
 
+			// Public keys
+			pubKeysMap.set(actor.id, actor.publicKey);
+
 			return actor;
 		} catch (e) {
 			return null;
@@ -68,13 +72,14 @@ Actors.assert = async (ids, options = {}) => {
 	const profiles = await activitypub.mocks.profile(actors);
 	const now = Date.now();
 
-	const bulkSet = profiles.map((profile) => {
-		if (!profile) {
-			return null;
+	const bulkSet = profiles.reduce((memo, profile) => {
+		if (profile) {
+			const key = `userRemote:${profile.uid}`;
+			memo.push([key, profile], [`${key}:keys`, pubKeysMap.get(profile.uid)]);
 		}
-		const key = `userRemote:${profile.uid}`;
-		return [key, profile];
-	}).filter(Boolean);
+
+		return memo;
+	}, []);
 	if (followersUrlMap.size) {
 		bulkSet.push(['followersUrl:uid', Object.fromEntries(followersUrlMap)]);
 	}
diff --git a/src/middleware/activitypub.js b/src/middleware/activitypub.js
index 79c3e19fe3..bdf28931fb 100644
--- a/src/middleware/activitypub.js
+++ b/src/middleware/activitypub.js
@@ -1,5 +1,6 @@
 'use strict';
 
+const db = require('../database');
 const meta = require('../meta');
 const activitypub = require('../activitypub');
 
@@ -39,11 +40,29 @@ middleware.validate = async function (req, res, next) {
 	}
 
 	// Sanity-check payload schema
-	const required = ['type'];
+	const required = ['type', 'actor', 'object'];
 	if (!required.every(prop => req.body.hasOwnProperty(prop))) {
 		return res.sendStatus(400);
 	}
 
+	const { actor, object } = req.body;
+
+	// Origin checking
+	const actorHostname = new URL(actor).hostname;
+	const objectHostname = new URL(typeof object === 'string' ? object : object.id).hostname;
+	if (actorHostname !== objectHostname) {
+		return res.sendStatus(403);
+	}
+
+	// Cross-check key ownership against received actor
+	await activitypub.actors.assert(actor);
+	const compare = await db.getObjectField(`userRemote:${actor}:keys`, 'id');
+	const { signature } = req.headers;
+	const keyId = new Map(signature.split(',').filter(Boolean).map(v => v.split('='))).get('keyId');
+	if (`"${compare}"` !== keyId) {
+		return res.sendStatus(403);
+	}
+
 	next();
 };
 
diff --git a/test/activitypub.js b/test/activitypub.js
index e1c052e377..936a7b0add 100644
--- a/test/activitypub.js
+++ b/test/activitypub.js
@@ -88,7 +88,7 @@ describe('ActivityPub integration', () => {
 
 		});
 
-		describe.only('.resolveId()', () => {
+		describe('.resolveId()', () => {
 			let url;
 			let resolved;