diff --git a/.env.sample b/.env.sample
index 65065fa2..86e32dd9 100644
--- a/.env.sample
+++ b/.env.sample
@@ -37,6 +37,7 @@ GITHUB_ACCESS_TOKEN=
 # AWS credentials (optional in dev)
 AWS_ACCESS_KEY_ID=notcheckedindev
 AWS_SECRET_ACCESS_KEY=notcheckedindev
+AWS_REGION=ap-xxxxx-1
 AWS_S3_UPLOAD_BUCKET_URL=http://s3:4569
 AWS_S3_UPLOAD_BUCKET_NAME=outline-dev
 AWS_S3_UPLOAD_MAX_SIZE=26214400
diff --git a/package.json b/package.json
index 4c460a0f..7c4908e1 100644
--- a/package.json
+++ b/package.json
@@ -188,4 +188,4 @@
     "rimraf": "^2.5.4"
   },
   "version": "0.17.0"
-}
+}
\ No newline at end of file
diff --git a/server/api/users.js b/server/api/users.js
index d3dd3212..8dc8f235 100644
--- a/server/api/users.js
+++ b/server/api/users.js
@@ -1,7 +1,13 @@
 // @flow
 import uuid from 'uuid';
 import Router from 'koa-router';
-import { makePolicy, signPolicy, publicS3Endpoint } from '../utils/s3';
+import format from 'date-fns/format';
+import {
+  makePolicy,
+  getSignature,
+  publicS3Endpoint,
+  makeCredential,
+} from '../utils/s3';
 import { ValidationError } from '../errors';
 import { Event, User, Team } from '../models';
 import auth from '../middlewares/authentication';
@@ -63,7 +69,9 @@ router.post('users.s3Upload', auth(), async ctx => {
 
   const s3Key = uuid.v4();
   const key = `uploads/${ctx.state.user.id}/${s3Key}/${filename}`;
-  const policy = makePolicy();
+  const credential = makeCredential();
+  const longDate = format(new Date(), 'YYYYMMDDTHHmmss\\Z');
+  const policy = makePolicy(credential, longDate);
   const endpoint = publicS3Endpoint();
   const url = `${endpoint}/${key}`;
 
@@ -84,13 +92,15 @@ router.post('users.s3Upload', auth(), async ctx => {
       maxUploadSize: process.env.AWS_S3_UPLOAD_MAX_SIZE,
       uploadUrl: endpoint,
       form: {
-        AWSAccessKeyId: process.env.AWS_ACCESS_KEY_ID,
         'Cache-Control': 'max-age=31557600',
         'Content-Type': kind,
-        key,
         acl: 'public-read',
-        signature: signPolicy(policy),
+        key,
         policy,
+        'x-amz-algorithm': 'AWS4-HMAC-SHA256',
+        'x-amz-credential': credential,
+        'x-amz-date': longDate,
+        'x-amz-signature': getSignature(policy),
       },
       asset: {
         contentType: kind,
diff --git a/server/utils/s3.js b/server/utils/s3.js
index 1e423390..77894272 100644
--- a/server/utils/s3.js
+++ b/server/utils/s3.js
@@ -8,9 +8,29 @@ import fetch from 'isomorphic-fetch';
 import bugsnag from 'bugsnag';
 
 const AWS_SECRET_ACCESS_KEY = process.env.AWS_SECRET_ACCESS_KEY;
+const AWS_ACCESS_KEY_ID = process.env.AWS_ACCESS_KEY_ID;
+const AWS_REGION = process.env.AWS_REGION;
 const AWS_S3_UPLOAD_BUCKET_NAME = process.env.AWS_S3_UPLOAD_BUCKET_NAME;
 
-export const makePolicy = () => {
+const hmac = (key: string, message: string, encoding: any) => {
+  return crypto
+    .createHmac('sha256', key)
+    .update(message, 'utf8')
+    .digest(encoding);
+};
+
+export const makeCredential = () => {
+  const credential =
+    AWS_ACCESS_KEY_ID +
+    '/' +
+    format(new Date(), 'YYYYMMDD') +
+    '/' +
+    AWS_REGION +
+    '/s3/aws4_request';
+  return credential;
+};
+
+export const makePolicy = (credential: string, longDate: string) => {
   const tomorrow = addHours(new Date(), 24);
   const policy = {
     conditions: [
@@ -20,6 +40,9 @@ export const makePolicy = () => {
       ['content-length-range', 0, +process.env.AWS_S3_UPLOAD_MAX_SIZE],
       ['starts-with', '$Content-Type', 'image'],
       ['starts-with', '$Cache-Control', ''],
+      { 'x-amz-algorithm': 'AWS4-HMAC-SHA256' },
+      { 'x-amz-credential': credential },
+      { 'x-amz-date': longDate },
     ],
     expiration: format(tomorrow, 'YYYY-MM-DDTHH:mm:ss\\Z'),
   };
@@ -27,13 +50,16 @@ export const makePolicy = () => {
   return new Buffer(JSON.stringify(policy)).toString('base64');
 };
 
-export const signPolicy = (policy: any) => {
-  invariant(AWS_SECRET_ACCESS_KEY, 'AWS_SECRET_ACCESS_KEY not set');
-  const signature = crypto
-    .createHmac('sha1', AWS_SECRET_ACCESS_KEY)
-    .update(policy)
-    .digest('base64');
+export const getSignature = (policy: any) => {
+  const kDate = hmac(
+    'AWS4' + AWS_SECRET_ACCESS_KEY,
+    format(new Date(), 'YYYYMMDD')
+  );
+  const kRegion = hmac(kDate, AWS_REGION);
+  const kService = hmac(kRegion, 's3');
+  const kCredentials = hmac(kService, 'aws4_request');
 
+  const signature = hmac(kCredentials, policy, 'hex');
   return signature;
 };