rewrite MegolmExportEncryption using async/await

... to make it easier to add exception handling

src/utils/MegolmExportEncryption.js

@@ -36,7 +36,7 @@ const subtleCrypto = window.crypto.subtle || window.crypto.webkitSubtle;
  * @param {String} password
  * @return {Promise<String>} promise for decrypted output
  */
-export function decryptMegolmKeyFile(data, password) {
+export async function decryptMegolmKeyFile(data, password) {
     const body = unpackMegolmKeyFile(data);
 
     // check we have a version byte
@@ -60,21 +60,20 @@ export function decryptMegolmKeyFile(data, password) {
     const ciphertext = body.subarray(37, 37+ciphertextLength);
     const hmac = body.subarray(-32);
 
-    return deriveKeys(salt, iterations, password).then((keys) => {
+    const [aesKey, hmacKey] = await deriveKeys(salt, iterations, password);
-        const [aesKey, hmacKey] = keys;
 
     const toVerify = body.subarray(0, -32);
-        return subtleCrypto.verify(
+    const isValid = await subtleCrypto.verify(
         {name: 'HMAC'},
         hmacKey,
         hmac,
         toVerify,
-        ).then((isValid) => {
+    );
     if (!isValid) {
         throw new Error('Authentication check failed: incorrect password?');
     }
 
-            return subtleCrypto.decrypt(
+    const plaintext = await subtleCrypto.decrypt(
         {
             name: "AES-CTR",
             counter: iv,
@@ -83,10 +82,8 @@ export function decryptMegolmKeyFile(data, password) {
         aesKey,
         ciphertext,
     );
-        });
+
-    }).then((plaintext) => {
     return new TextDecoder().decode(new Uint8Array(plaintext));
-    });
 }
 
 
@@ -100,7 +97,7 @@ export function decryptMegolmKeyFile(data, password) {
  *    key-derivation function.
  * @return {Promise<ArrayBuffer>} promise for encrypted output
  */
-export function encryptMegolmKeyFile(data, password, options) {
+export async function encryptMegolmKeyFile(data, password, options) {
     options = options || {};
     const kdfRounds = options.kdf_rounds || 500000;
 
@@ -115,10 +112,9 @@ export function encryptMegolmKeyFile(data, password, options) {
     // of a single bit of iv is a price we have to pay.
     iv[9] &= 0x7f;
 
-    return deriveKeys(salt, kdfRounds, password).then((keys) => {
+    const [aesKey, hmacKey] = await deriveKeys(salt, kdfRounds, password);
-        const [aesKey, hmacKey] = keys;
 
-        return subtleCrypto.encrypt(
+    const ciphertext = await subtleCrypto.encrypt(
         {
             name: "AES-CTR",
             counter: iv,
@@ -126,7 +122,8 @@ export function encryptMegolmKeyFile(data, password, options) {
         },
         aesKey,
         new TextEncoder().encode(data),
-        ).then((ciphertext) => {
+    );
+
     const cipherArray = new Uint8Array(ciphertext);
     const bodyLength = (1+salt.length+iv.length+4+cipherArray.length+32);
     const resultBuffer = new Uint8Array(bodyLength);
@@ -142,17 +139,15 @@ export function encryptMegolmKeyFile(data, password, options) {
 
     const toSign = resultBuffer.subarray(0, idx);
 
-            return subtleCrypto.sign(
+    const hmac = await subtleCrypto.sign(
         {name: 'HMAC'},
         hmacKey,
         toSign,
-            ).then((hmac) => {
+    );
-                hmac = new Uint8Array(hmac);
+
-                resultBuffer.set(hmac, idx);
+    const hmacArray = new Uint8Array(hmac);
+    resultBuffer.set(hmacArray, idx);
     return packMegolmKeyFile(resultBuffer);
-            });
-        });
-    });
 }
 
 /**
@@ -163,16 +158,17 @@ export function encryptMegolmKeyFile(data, password, options) {
  * @param {String} password  password
  * @return {Promise<[CryptoKey, CryptoKey]>} promise for [aes key, hmac key]
  */
-function deriveKeys(salt, iterations, password) {
+async function deriveKeys(salt, iterations, password) {
     const start = new Date();
-    return subtleCrypto.importKey(
+    const key = await subtleCrypto.importKey(
         'raw',
         new TextEncoder().encode(password),
         {name: 'PBKDF2'},
         false,
         ['deriveBits'],
-    ).then((key) => {
+    );
-        return subtleCrypto.deriveBits(
+
+    const keybits = await subtleCrypto.deriveBits(
         {
             name: 'PBKDF2',
             salt: salt,
@@ -182,7 +178,7 @@ function deriveKeys(salt, iterations, password) {
         key,
         512,
     );
-    }).then((keybits) => {
+
     const now = new Date();
     console.log("E2e import/export: deriveKeys took " + (now - start) + "ms");
 
@@ -206,8 +202,7 @@ function deriveKeys(salt, iterations, password) {
         false,
         ['sign', 'verify'],
     );
-        return Promise.all([aesProm, hmacProm]);
+    return await Promise.all([aesProm, hmacProm]);
-    });
 }
 
 const HEADER_LINE = '-----BEGIN MEGOLM SESSION DATA-----';

test/utils/MegolmExportEncryption-test.js

@@ -81,15 +81,23 @@ describe('MegolmExportEncryption', function() {
     describe('decrypt', function() {
         it('should handle missing header', function() {
             const input=stringToArray(`-----`);
-            expect(()=>MegolmExportEncryption.decryptMegolmKeyFile(input, ''))
+            return MegolmExportEncryption.decryptMegolmKeyFile(input, '')
-                .toThrow('Header line not found');
+            .then((res) => {
+                throw new Error('expected to throw');
+            }, (error) => {
+                expect(error.message).toEqual('Header line not found');
+            });
         });
 
         it('should handle missing trailer', function() {
             const input=stringToArray(`-----BEGIN MEGOLM SESSION DATA-----
 -----`);
-            expect(()=>MegolmExportEncryption.decryptMegolmKeyFile(input, ''))
+            return MegolmExportEncryption.decryptMegolmKeyFile(input, '')
-                .toThrow('Trailer line not found');
+            .then((res) => {
+                throw new Error('expected to throw');
+            }, (error) => {
+                expect(error.message).toEqual('Trailer line not found');
+            });
         });
 
         it('should handle a too-short body', function() {
@@ -98,8 +106,12 @@ AXNhbHRzYWx0c2FsdHNhbHSIiIiIiIiIiIiIiIiIiIiIAAAACmIRUW2OjZ3L2l6j9h0lHlV3M2dx
 cissyYBxjsfsAn
 -----END MEGOLM SESSION DATA-----
 `);
-            expect(()=>MegolmExportEncryption.decryptMegolmKeyFile(input, ''))
+            return MegolmExportEncryption.decryptMegolmKeyFile(input, '')
-                .toThrow('Invalid file: too short');
+            .then((res) => {
+                throw new Error('expected to throw');
+            }, (error) => {
+                expect(error.message).toEqual('Invalid file: too short');
+            });
         });
 
         it('should decrypt a range of inputs', function(done) {