diff --git a/.vscode/launch.json b/.vscode/launch.json
index d8ad498..759635f 100644
--- a/.vscode/launch.json
+++ b/.vscode/launch.json
@@ -7,7 +7,7 @@
 		{
 			"type": "node",
 			"request": "launch",
-			"name": "Generate",
+			"name": "Run",
 			"program": "${workspaceFolder}/lib/index.ts",
 			"preLaunchTask": "tsc: build - tsconfig.json",
 			"outFiles": [
diff --git a/lib/activitypub/activity.ts b/lib/activitypub/activity.ts
index 3c0d13d..365fded 100644
--- a/lib/activitypub/activity.ts
+++ b/lib/activitypub/activity.ts
@@ -37,4 +37,7 @@ export interface Note extends Activity {
 export interface Actor {
 	id: string;
 	inbox: string;
+	publicKey: {
+		publicKeyPem: string;
+	};
 }
\ No newline at end of file
diff --git a/lib/activitypub/actor.ts b/lib/activitypub/actor.ts
index a259547..7d193e8 100644
--- a/lib/activitypub/actor.ts
+++ b/lib/activitypub/actor.ts
@@ -3,9 +3,7 @@ import { promises as fs } from "fs";
 
 const domain = process.env.DOMAIN;
 
-export default async function actor(): Promise<Router> {
-	const router = Router();
-
+export default async function actor(router: Router) {
 	const pubKeyPem = (await fs.readFile(process.env.PUB_KEY_PEM!)).toString();
 	const actorObj = {
 		"@context": [
@@ -39,6 +37,4 @@ export default async function actor(): Promise<Router> {
 			res.redirect("/");
 		}
 	});
-
-	return router;
 }
\ No newline at end of file
diff --git a/lib/activitypub/articles.ts b/lib/activitypub/articles.ts
index 00f47c4..8608db1 100644
--- a/lib/activitypub/articles.ts
+++ b/lib/activitypub/articles.ts
@@ -54,9 +54,7 @@ export async function toFederate(db: Database): Promise<[string, Article][]> {
 	});
 }
 
-export function router(): Router {
-	const router = Router();
-
+export function route(router: Router) {
 	router.use("/:category/:year/:slug/", (req, res, next) => {
 		if (req.accepts("text/html")) {
 			next();
@@ -74,6 +72,4 @@ export function router(): Router {
 			});
 		}
 	});
-
-	return router;
 }
\ No newline at end of file
diff --git a/lib/activitypub/federate.ts b/lib/activitypub/federate.ts
index 517f75d..5f45dc5 100644
--- a/lib/activitypub/federate.ts
+++ b/lib/activitypub/federate.ts
@@ -49,9 +49,8 @@ export async function signAndSend(activity: Activity, inbox: string) {
 	const stringToSign = `(request-target): post ${inboxFragment}\nhost: ${targetDomain}\ndate: ${date.toUTCString()}`;
 	signer.update(stringToSign);
 	signer.end();
-	const signature = signer.sign(privKey);
-	const base64Signature = signature.toString("base64");
-	const header = `keyId="https://${domain}/ap/actor#main-key",headers="(request-target) host date",signature="${base64Signature}"`;
+	const signature = signer.sign(privKey, "base64");
+	const header = `keyId="https://${domain}/ap/actor#main-key",headers="(request-target) host date",signature="${signature}"`;
 	console.log("Sending:", activity);
 	console.log("stringToSign:", stringToSign);
 	console.log("Signature: " + header);
diff --git a/lib/activitypub/followers.ts b/lib/activitypub/followers.ts
index 13d7c9a..df09ae3 100644
--- a/lib/activitypub/followers.ts
+++ b/lib/activitypub/followers.ts
@@ -3,9 +3,7 @@ import { Database } from "sqlite3";
 
 const domain = process.env.DOMAIN;
 
-export default function followers(): Router {
-	const router = Router();
-
+export default function followers(router: Router) {
 	router.get("/ap/actor/followers", (req, res) => {
 		const db = <Database>req.app.get("db");
 
@@ -22,6 +20,4 @@ export default function followers(): Router {
 			res.end();
 		});
 	});
-
-	return router;
 }
\ No newline at end of file
diff --git a/lib/activitypub/inbox.ts b/lib/activitypub/inbox.ts
index 5839013..e960b37 100644
--- a/lib/activitypub/inbox.ts
+++ b/lib/activitypub/inbox.ts
@@ -7,13 +7,9 @@ import { URL } from "url";
 
 const domain = process.env.DOMAIN;
 
-export default function inbox(): Router {
-	const router = Router();
-
+export default function inbox(router: Router) {
 	router.post("/ap/inbox", handleInbox);
 	router.post("/inbox", handleInbox);
-
-	return router;
 }
 
 async function handleInbox(req: Request, res: Response) {
diff --git a/lib/activitypub/middleware/http-signature.ts b/lib/activitypub/middleware/http-signature.ts
new file mode 100644
index 0000000..bb534be
--- /dev/null
+++ b/lib/activitypub/middleware/http-signature.ts
@@ -0,0 +1,44 @@
+import crypto, { createVerify } from "crypto";
+import { Request, Response, NextFunction } from "express";
+import { fetchActor } from "../federate";
+import { IncomingHttpHeaders } from "http";
+
+export = async (req: Request, res: Response, next: NextFunction) => {
+	if (req.method !== "POST") {
+		next();
+		return;
+	}
+	const actor = await fetchActor(req.body.actor as string);
+	if (validate(req, actor.publicKey.publicKeyPem)) {
+		next();
+	} else {
+		console.log(`Could not validate HTTP signature for ${req.body.actor}`);
+		res.status(401).end("Could not validate HTTP signature");
+	}
+};
+
+function validate(req: Request, publicKeyPem: string): boolean {
+	const signature = parseSignature(req.header("signature")!);
+	const usedHeaders = signature.get("headers")!.split(/\s/);
+	const signingString = usedHeaders.map(header => {
+		const value = header === "(request-target)" ? `${req.method} ${req.path}`.toLowerCase() : req.header(header);
+		return `${header}: ${value}`;
+	}).join("\n");
+	const verifier = crypto.createVerify("sha256");
+	verifier.update(signingString);
+	verifier.end();
+	return verifier.verify(publicKeyPem, signature.get("signature")!, "base64");
+}
+
+function parseSignature(signature: string): Map<string, string> {
+	const map = new Map<string, string>();
+	map.set("headers", "date");
+	for (const part of signature.split(",")) {
+		const index = part.indexOf("=");
+		const key = part.substring(0, index);
+		const value = part.substring(index + 1);
+		const unquoted = value.replace(/^"+|"+$/g, ""); // strip leading and trailing quotes
+		map.set(key, unquoted);
+	}
+	return map;
+}
\ No newline at end of file
diff --git a/lib/activitypub/webfinger.ts b/lib/activitypub/webfinger.ts
index 9d9b2ef..383a3d2 100644
--- a/lib/activitypub/webfinger.ts
+++ b/lib/activitypub/webfinger.ts
@@ -2,9 +2,7 @@ import express, { Router } from "express";
 
 const domain = process.env.DOMAIN;
 
-export default function webfinger(): Router {
-	const router = Router();
-
+export default function webfinger(router: Router) {
 	router.get("/.well-known/webfinger", (req, res) => {
 		res.json({
 			"subject": `acct:shadowfacts@${domain}`,
@@ -18,6 +16,4 @@ export default function webfinger(): Router {
 		});
 		res.end();
 	});
-
-	return router;
 }
\ No newline at end of file
diff --git a/lib/index.ts b/lib/index.ts
index 892d13f..9be5390 100644
--- a/lib/index.ts
+++ b/lib/index.ts
@@ -1,10 +1,11 @@
 import { Page } from "./metadata";
 import generators from "./generate";
 
-import express from "express";
+import express, { Router } from "express";
 import morgan from "morgan";
 import bodyParser from "body-parser";
 import activitypub from "./activitypub";
+import validateHttpSig from "./activitypub/middleware/http-signature";
 
 import sqlite3 from "sqlite3";
 
@@ -43,12 +44,14 @@ app.use(bodyParser.json({ type: "application/activity+json" }));
 	await activitypub.articles.setup(posts, db);
 	const toFederate = await activitypub.articles.toFederate(db);
 
-	
-	app.use(await activitypub.actor());
-	app.use(activitypub.followers());
-	app.use(activitypub.inbox());
-	app.use(activitypub.webfinger());
-	app.use(activitypub.articles.router());
+	const apRouter = Router();
+	apRouter.use(validateHttpSig);
+	await activitypub.actor(apRouter);
+	activitypub.followers(apRouter);
+	activitypub.inbox(apRouter);
+	activitypub.webfinger(apRouter);
+	activitypub.articles.route(apRouter);
+	app.use(apRouter);
 	app.use(express.static("out"));
 
 	const port = process.env.PORT || 8083;