making webassembly optional, ensuring retry button works when wrong password is provided

Tested configurations:
- browser with WASM support (Firefox 68.0.2)
  - creates paste with zlib compression, no password
  - creates paste with zlib compression, with password
  - reads paste with zlib compression, no password
  - reads paste with zlib compression, with password + retry button works
  - reads paste without compression, no password
  - reads paste without compression, with password + retry button works
- browser without WASM support (Chromium 76.0.3809.100, started via `chromium-browser --js-flags=--noexpose_wasm`)
  - creates paste without compression, no password, but shows WASM warning
  - creates paste without compression, with password, but shows WASM warning
  - fails to read paste with zlib compression, no password + shows WASM error
  - fails to read paste with zlib compression, with password + shows WASM error
  - reads paste without compression, no password
  - reads paste without compression, with password + retry button works

js/privatebin.js

@@ -780,15 +780,19 @@ jQuery.PrivateBin = (function($, RawDeflate) {
          * @private
          * @param  {string} message
          * @param  {string} mode
+         * @param  {object} zlib
+         * @throws {string}
          * @return {ArrayBuffer} data
          */
-        async function compress(message, mode)
+        async function compress(message, mode, zlib)
         {
             message = stringToArraybuffer(
                 utf16To8(message)
             );
             if (mode === 'zlib') {
-                let zlib = (await z);
+                if (typeof zlib === 'undefined') {
+                    throw 'Error compressing paste, due to missing WebAssembly support.'
+                }
                 return zlib.deflate(message).buffer;
             }
             return message;
@@ -803,16 +807,16 @@ jQuery.PrivateBin = (function($, RawDeflate) {
          * @private
          * @param  {ArrayBuffer} data
          * @param  {string} mode
+         * @param  {object} zlib
+         * @throws {string}
          * @return {string} message
          */
-        async function decompress(data, mode)
+        async function decompress(data, mode, zlib)
         {
             if (mode === 'zlib' || mode === 'none') {
                 if (mode === 'zlib') {
-                    let zlib = (await z);
                     if (typeof zlib === 'undefined') {
-                        Alert.showError('Your browser doesn\'t support WebAssembly, used for zlib compression. You can create uncompressed documents, but can\'t read compressed ones.')
+                        throw 'Error decompressing paste, due to missing WebAssembly support.'
-                        return '';
                     }
                     data = zlib.inflate(
                         new Uint8Array(data)
@@ -962,12 +966,13 @@ jQuery.PrivateBin = (function($, RawDeflate) {
          */
         me.cipher = async function(key, password, message, adata)
         {
+            let zlib = (await z);
             // AES in Galois Counter Mode, keysize 256 bit,
             // authentication tag 128 bit, 10000 iterations in key derivation
             const compression = (
-                    typeof (await z) === 'undefined' ?
+                    typeof zlib === 'undefined' ?
                     'none' : // client lacks support for WASM
-                    $('body').data('compression') || 'zlib'
+                    ($('body').data('compression') || 'zlib')
                 ),
                 spec = [
                     getRandomBytes(16), // initialization vector
@@ -997,7 +1002,7 @@ jQuery.PrivateBin = (function($, RawDeflate) {
                         await window.crypto.subtle.encrypt(
                             cryptoSettings(JSON.stringify(adata), spec),
                             await deriveKey(key, password, spec),
-                            await compress(message, compression)
+                            await compress(message, compression, zlib)
                         ).catch(Alert.showError)
                     )
                 ),
@@ -1018,7 +1023,8 @@ jQuery.PrivateBin = (function($, RawDeflate) {
          */
         me.decipher = async function(key, password, data)
         {
-            let adataString, spec, cipherMessage;
+            let adataString, spec, cipherMessage, plaintext;
+            let zlib = (await z);
             if (data instanceof Array) {
                 // version 2
                 adataString = JSON.stringify(data[1]);
@@ -1045,20 +1051,29 @@ jQuery.PrivateBin = (function($, RawDeflate) {
             }
             spec[0] = atob(spec[0]);
             spec[1] = atob(spec[1]);
+            if (spec[7] === 'zlib') {
+                if (typeof zlib === 'undefined') {
+                    throw 'Error decompressing paste, due to missing WebAssembly support.'
+                }
+            }
             try {
-                return await decompress(
+                plaintext = await window.crypto.subtle.decrypt(
-                    await window.crypto.subtle.decrypt(
                     cryptoSettings(adataString, spec),
                     await deriveKey(key, password, spec),
                     stringToArraybuffer(
                         atob(cipherMessage)
                     )
-                    ).catch(Alert.showError),
-                    spec[7]
                 );
             } catch(err) {
+                console.error(err);
                 return '';
             }
+            try {
+                return await decompress(plaintext, spec[7], zlib);
+            } catch(err) {
+                Alert.showError(err);
+                return err;
+            }
         };
 
         /**
@@ -4522,7 +4537,7 @@ jQuery.PrivateBin = (function($, RawDeflate) {
 
             // if all tries failed, we can only return an error
             if (plaindata.length === 0) {
-                throw 'failed to decipher data';
+                return false;
             }
 
             return plaindata;
@@ -4551,8 +4566,11 @@ jQuery.PrivateBin = (function($, RawDeflate) {
                 if (password.length === 0) {
                     throw 'waiting on user to provide a password';
                 } else {
-                    displayDecryptionError('failed to decipher paste text: Incorrect password?');
+                    Alert.hideLoading();
-                    throw 'waiting on user to provide correct password';
+                    // reset password, so it can be re-entered
+                    Prompt.reset();
+                    TopNav.showRetryButton();
+                    throw 'Could not decrypt data. Did you enter a wrong password? Retry with the button at the top.';
                 }
             }
 
@@ -4642,27 +4660,6 @@ jQuery.PrivateBin = (function($, RawDeflate) {
             });
         }
 
-        /**
-         * displays and logs decryption errors
-         *
-         * @name   PasteDecrypter.displayDecryptionError
-         * @private
-         * @function
-         * @param  {string} message
-         */
-        function displayDecryptionError(message)
-        {
-            Alert.hideLoading();
-
-            // log detailed error, but display generic translation
-            console.error(message);
-            Alert.showError('Could not decrypt data. Did you enter a wrong password? Retry with the button at the top.');
-
-            // reset password, so it can be re-entered
-            Prompt.reset();
-            TopNav.showRetryButton();
-        }
-
         /**
          * show decrypted text in the display area, including discussion (if open)
          *
@@ -4714,7 +4711,7 @@ jQuery.PrivateBin = (function($, RawDeflate) {
                 .catch((err) => {
                     // wait for the user to type in the password,
                     // then PasteDecrypter.run will be called again
-                    console.error(err);
+                    Alert.showError(err);
                 });
         };
 
@@ -4818,34 +4815,14 @@ jQuery.PrivateBin = (function($, RawDeflate) {
                 'subtle' in window.crypto &&
                 'encrypt' in window.crypto.subtle &&
                 'decrypt' in window.crypto.subtle &&
+                'Uint8Array' in window &&
                 'Uint32Array' in window
             )) {
                 return true;
             }
 
-            if (!(
+             // not checking for async/await, ES6 or Promise support, as most
-                'WebAssembly' in window &&
+             // browsers introduced these earlier then webassembly and webcrypto:
-                'instantiate' in window.WebAssembly
-            )) {
-                return true;
-            }
-            try {
-                // [\0, 'a', 's', 'm', (uint_32) 1] - smallest valid wasm module
-                const module = new WebAssembly.Module(Uint8Array.of(0x0, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00));
-                if (
-                    !(
-                        module instanceof WebAssembly.Module &&
-                        new WebAssembly.Instance(module) instanceof WebAssembly.Instance
-                    )
-                ) {
-                    return true;
-                }
-            } catch (e) {
-                return true;
-            }
-
-             // not checking for async/await, ES6, Promise or Uint8Array support,
-             // as most browsers introduced these earlier then webassembly and webcrypto:
              // https://github.com/PrivateBin/PrivateBin/pull/431#issuecomment-493129359
 
             return false;
@@ -4881,7 +4858,9 @@ jQuery.PrivateBin = (function($, RawDeflate) {
             }
 
             z = zlib.catch(function () {
+                if ($('body').data('compression') !== 'none') {
                     Alert.showWarning('Your browser doesn\'t support WebAssembly, used for zlib compression. You can create uncompressed documents, but can\'t read compressed ones.');
+                }
             });
             return true;
         }

js/test/CryptTool.js

@@ -8,9 +8,6 @@ describe('CryptTool', function () {
             await new Promise(resolve => setTimeout(resolve, 1900));
         });
 
-        // ensure zlib is getting loaded
-        $.PrivateBin.InitialCheck.init();
-
         this.timeout(30000);
         it('can en- and decrypt any message', function () {
             jsc.assert(jsc.forall(
@@ -21,6 +18,8 @@ describe('CryptTool', function () {
                     // pause to let async functions conclude
                     await new Promise(resolve => setTimeout(resolve, 300));
                     let clean = jsdom();
+                    // ensure zlib is getting loaded
+                    $.PrivateBin.InitialCheck.init();
                     window.crypto = new WebCrypto();
                     message = message.trim();
                     let cipherMessage = await $.PrivateBin.CryptTool.cipher(
@@ -182,6 +181,8 @@ describe('CryptTool', function () {
             let message = fs.readFileSync('test/compression-sample.txt', 'utf8'),
                 clean = jsdom();
             window.crypto = new WebCrypto();
+            // ensure zlib is getting loaded
+            $.PrivateBin.InitialCheck.init();
             let cipherMessage = await $.PrivateBin.CryptTool.cipher(
                     'foo', 'bar', message, []
                 ),
@@ -225,6 +226,8 @@ isWhile : interp (while expr sBody) (MemElem mem) =
 conseq_or_bottom inv (interp (nth_iterate sBody n) (MemElem mem))
 `;
                     let clean = jsdom();
+                    // ensure zlib is getting loaded
+                    $.PrivateBin.InitialCheck.init();
                     window.crypto = new WebCrypto();
                     let cipherMessage = await $.PrivateBin.CryptTool.cipher(
                             key, password, message, []

tpl/bootstrap.php

@@ -71,7 +71,7 @@ if ($MARKDOWN):
 endif;
 ?>
 		<script type="text/javascript" data-cfasync="false" src="js/purify-1.0.11.js" integrity="sha512-p7UyJuyBkhMcMgE4mDsgK0Lz70OvetLefua1oXs1OujWv9gOxh4xy8InFux7bZ4/DAZsTmO4rgVwZW9BHKaTaw==" crossorigin="anonymous"></script>
-		<script type="text/javascript" data-cfasync="false" src="js/privatebin.js?<?php echo rawurlencode($VERSION); ?>" integrity="sha512-dsFOXy6/2JHcWi9jwtIIBmAwkRc/2cHDON5YONEo9yFZ7Mt//UFszzk3/kKM77JRDvkHC9gvK/ucgsYT+gyUVw==" crossorigin="anonymous"></script>
+		<script type="text/javascript" data-cfasync="false" src="js/privatebin.js?<?php echo rawurlencode($VERSION); ?>" integrity="sha512-tTyV/T13WEwhn9bKY1N0PVu5UFctbDY1qosTTrslVq0R3vPTPjjxSMbUZ3FZBf01rXu39HPV/ibQiD2fOEjYcA==" crossorigin="anonymous"></script>
 		<!--[if IE]>
 		<style type="text/css">body {padding-left:60px;padding-right:60px;} #ienotice {display:block;}</style>
 		<![endif]-->

tpl/page.php

@@ -49,7 +49,7 @@ if ($MARKDOWN):
 endif;
 ?>
 		<script type="text/javascript" data-cfasync="false" src="js/purify-1.0.11.js" integrity="sha512-p7UyJuyBkhMcMgE4mDsgK0Lz70OvetLefua1oXs1OujWv9gOxh4xy8InFux7bZ4/DAZsTmO4rgVwZW9BHKaTaw==" crossorigin="anonymous"></script>
-		<script type="text/javascript" data-cfasync="false" src="js/privatebin.js?<?php echo rawurlencode($VERSION); ?>" integrity="sha512-dsFOXy6/2JHcWi9jwtIIBmAwkRc/2cHDON5YONEo9yFZ7Mt//UFszzk3/kKM77JRDvkHC9gvK/ucgsYT+gyUVw==" crossorigin="anonymous"></script>
+		<script type="text/javascript" data-cfasync="false" src="js/privatebin.js?<?php echo rawurlencode($VERSION); ?>" integrity="sha512-tTyV/T13WEwhn9bKY1N0PVu5UFctbDY1qosTTrslVq0R3vPTPjjxSMbUZ3FZBf01rXu39HPV/ibQiD2fOEjYcA==" crossorigin="anonymous"></script>
 		<!--[if IE]>
 		<style type="text/css">body {padding-left:60px;padding-right:60px;} #ienotice {display:block;}</style>
 		<![endif]-->