diff --git a/package.json b/package.json
index 498514a2b0..3bcccd668e 100644
--- a/package.json
+++ b/package.json
@@ -42,6 +42,7 @@
   },
   "dependencies": {
     "babel-runtime": "^6.11.6",
+    "browser-encrypt-attachment": "0.0.0",
     "browser-request": "^0.3.3",
     "classnames": "^2.1.2",
     "draft-js": "^0.8.1",
diff --git a/src/ContentMessages.js b/src/ContentMessages.js
index fd18b22d30..a3f6d548c3 100644
--- a/src/ContentMessages.js
+++ b/src/ContentMessages.js
@@ -23,6 +23,8 @@ var MatrixClientPeg = require('./MatrixClientPeg');
 var sdk = require('./index');
 var Modal = require('./Modal');
 
+var encrypt = require("browser-encrypt-attachment");
+
 function infoForImageFile(imageFile) {
     var deferred = q.defer();
 
@@ -81,6 +83,24 @@ function infoForVideoFile(videoFile) {
     return deferred.promise;
 }
 
+/**
+ * Read the file as an ArrayBuffer.
+ * @return {Promise} A promise that resolves with an ArrayBuffer when the file
+ *   is read.
+ */
+function readFileAsArrayBuffer(file) {
+    var deferred = q.defer();
+    var reader = new FileReader();
+    reader.onload = function(e) {
+        deferred.resolve(e.target.result);
+    };
+    reader.onerror = function(e) {
+        deferred.reject(e);
+    };
+    reader.readAsArrayBuffer(file);
+    return deferred.promise;
+}
+
 
 class ContentMessages {
     constructor() {
@@ -137,10 +157,26 @@ class ContentMessages {
         this.inprogress.push(upload);
         dis.dispatch({action: 'upload_started'});
 
+        var encryptInfo = null;
         var error;
         var self = this;
         return def.promise.then(function() {
-            upload.promise = matrixClient.uploadContent(file);
+            if (matrixClient.isRoomEncrypted(room_id)) {
+                // If the room is encrypted then encrypt the file before uploading it.
+                // First read the file into memory.
+                upload.promise = readFileAsArrayBuffer(file).then(function(data) {
+                    // Then encrypt the file.
+                    return encrypt.encryptAttachment(data);
+                }).then(function(encryptResult) {
+                    // Record the information needed to decrypt the attachment.
+                    encryptInfo = encryptResult.info;
+                    // Pass the encrypted data as a Blob to the uploader.
+                    var blob = new Blob([encryptResult.data]);
+                    return matrixClient.uploadContent(blob);
+                });
+            } else {
+                upload.promise = matrixClient.uploadContent(file);
+            }
             return upload.promise;
         }).progress(function(ev) {
             if (ev) {
@@ -149,7 +185,16 @@ class ContentMessages {
                 dis.dispatch({action: 'upload_progress', upload: upload});
             }
         }).then(function(url) {
-            content.url = url;
+            if (encryptInfo === null) {
+                // If the attachment isn't encrypted then include the URL directly.
+                content.url = url;
+            } else {
+                // If the attachment is encrypted then bundle the URL along
+                // with the information needed to decrypt the attachment and
+                // add it under a file key.
+                encryptInfo.url = url;
+                content.file = encryptInfo;
+            }
             return matrixClient.sendMessage(roomId, content);
         }, function(err) {
             error = err;
diff --git a/src/components/views/messages/MImageBody.js b/src/components/views/messages/MImageBody.js
index 526fc6a3a5..087a337bd2 100644
--- a/src/components/views/messages/MImageBody.js
+++ b/src/components/views/messages/MImageBody.js
@@ -19,12 +19,18 @@ limitations under the License.
 var React = require('react');
 var filesize = require('filesize');
 
+// Pull in the encryption lib so that we can decrypt attachments.
+var encrypt = require("browser-encrypt-attachment");
+// Pull in a fetch polyfill so we can download encrypted attachments.
+require("isomorphic-fetch");
+
 var MatrixClientPeg = require('../../../MatrixClientPeg');
 var ImageUtils = require('../../../ImageUtils');
 var Modal = require('../../../Modal');
 var sdk = require('../../../index');
 var dis = require("../../../dispatcher");
 
+
 module.exports = React.createClass({
     displayName: 'MImageBody',
 
@@ -85,6 +91,33 @@ module.exports = React.createClass({
     componentDidMount: function() {
         this.dispatcherRef = dis.register(this.onAction);
         this.fixupHeight();
+        var content = this.props.mxEvent.getContent();
+        if (content.file !== undefined) {
+            // TODO: hook up an error handler to the promise.
+            this.decryptFile(content.file);
+        }
+    },
+
+    decryptFile: function(file) {
+        var url = MatrixClientPeg.get().mxcUrlToHttp(file.url);
+        var self = this;
+        // Download the encrypted file as an array buffer.
+        return fetch(url).then(function (response) {
+            return response.arrayBuffer();
+        }).then(function (responseData) {
+            // Decrypt the array buffer using the information taken from
+            // the event content.
+            return encrypt.decryptAttachment(responseData, file);
+        }).then(function(dataArray) {
+            // Turn the array into a Blob and use createObjectURL to make
+            // a url that we can use as an img src.
+            var blob = new Blob([dataArray]);
+            var blobUrl = window.URL.createObjectURL(blob);
+            self.refs.image.src = blobUrl;
+            self.refs.image.onload = function() {
+                window.URL.revokeObjectURL(blobUrl);
+            };
+        });
     },
 
     componentWillUnmount: function() {
@@ -148,7 +181,16 @@ module.exports = React.createClass({
         }
 
         var thumbUrl = this._getThumbUrl();
-        if (thumbUrl) {
+        if (content.file !== undefined) {
+            // Need to decrypt the attachment
+            // The attachment is decrypted in componentDidMount.
+            return (
+                <span className="mx_MImageBody" ref="body">
+                <img className="mx_MImageBody_thumbnail" src="img/encrypted-placeholder.svg" ref="image"
+                    alt={content.body} />
+                </span>
+            );
+        } else if (thumbUrl) {
             return (
                 <span className="mx_MImageBody" ref="body">
                     <a href={cli.mxcUrlToHttp(content.url)} onClick={ this.onClick }>