From dc4682eaf5606cb58cb0447bc9738e26f414561a Mon Sep 17 00:00:00 2001
From: Abhinav Adduri <abhinadduri@gmail.com>
Date: Mon, 10 Jul 2017 11:25:03 -0700
Subject: [PATCH] added checksums

---
 frontend/src/fileReceiver.js | 27 ++++++++++++++++++++++++---
 frontend/src/fileSender.js   | 19 +++++++++++--------
 2 files changed, 35 insertions(+), 11 deletions(-)

diff --git a/frontend/src/fileReceiver.js b/frontend/src/fileReceiver.js
index 5e363140..d6b8cc00 100644
--- a/frontend/src/fileReceiver.js
+++ b/frontend/src/fileReceiver.js
@@ -68,17 +68,38 @@ class FileReceiver extends EventEmitter {
           {
             name: 'AES-GCM',
             iv: hexToArray(fdata.iv),
-            additionalData: hexToArray(fdata.aad),
-            tagLength: 128
+            additionalData: hexToArray(fdata.aad)
           },
           key,
           fdata.data
         ),
         new Promise((resolve, reject) => {
           resolve(fdata.filename);
+        }),
+        new Promise((resolve, reject) => {
+          resolve(hexToArray(fdata.aad));
         })
       ]);
-    });
+    }).then(([decrypted, fname, proposedHash]) => {
+      return window.crypto.subtle.digest('SHA-256', decrypted).then(calculatedHash => {
+        const integrity = new Uint8Array(calculatedHash).toString() === proposedHash.toString();
+        if (!integrity) {
+          return new Promise((resolve, reject) => {
+            console.log('This file has been tampered with.')
+            reject();
+          })
+        }
+        
+        return Promise.all([
+          new Promise((resolve, reject) => {
+            resolve(decrypted);
+          }),
+          new Promise((resolve, reject) => {
+            resolve(fname);
+          })
+        ]);
+      })
+    })
   }
 }
 
diff --git a/frontend/src/fileSender.js b/frontend/src/fileSender.js
index 132b868c..ee433928 100644
--- a/frontend/src/fileSender.js
+++ b/frontend/src/fileSender.js
@@ -8,7 +8,6 @@ class FileSender extends EventEmitter {
     super();
     this.file = file;
     this.iv = window.crypto.getRandomValues(new Uint8Array(12));
-    this.aad = window.crypto.getRandomValues(new Uint8Array(6));
   }
 
   static delete(fileId, token) {
@@ -54,28 +53,32 @@ class FileSender extends EventEmitter {
         const reader = new FileReader();
         reader.readAsArrayBuffer(this.file);
         reader.onload = function(event) {
-          resolve(new Uint8Array(this.result));
+          const plaintext = new Uint8Array(this.result);
+          window.crypto.subtle.digest('SHA-256', plaintext).then(hash => {
+            resolve({plaintext: plaintext, hash: new Uint8Array(hash)});
+          })
         };
       })
     ])
-      .then(([secretKey, plaintext]) => {
+      .then(([secretKey, file]) => {
         return Promise.all([
           window.crypto.subtle
             .encrypt(
               {
                 name: 'AES-GCM',
                 iv: this.iv,
-                additionalData: this.aad,
+                additionalData: file.hash,
                 tagLength: 128
               },
               secretKey,
-              plaintext
+              file.plaintext
             )
             .catch(err => console.log('Error with encrypting.')),
-          window.crypto.subtle.exportKey('jwk', secretKey)
+          window.crypto.subtle.exportKey('jwk', secretKey),
+          new Promise((resolve, reject) => { resolve(file.hash) })
         ]);
       })
-      .then(([encrypted, keydata]) => {
+      .then(([encrypted, keydata, hash]) => {
         return new Promise((resolve, reject) => {
           const file = this.file;
           const fileId = arrayToHex(this.iv);
@@ -110,7 +113,7 @@ class FileSender extends EventEmitter {
           xhr.setRequestHeader(
             'X-File-Metadata',
             JSON.stringify({
-              aad: arrayToHex(this.aad),
+              aad: arrayToHex(hash),
               iv: fileId,
               filename: file.name
             })