Archives For July 2011

I have uploaded the latest DOMCrypt addon, which is version 0.4. It is not reviewed by the Addons team yet.
https://addons.mozilla.org/en-US/firefox/addon/domcrypt/versions/?page=1#version-0.4
I have updated it here as well:
http://mozilla.ddahl.com/domcrypt/extension/built/domcrypt.xpi

(note: The DOMCrypt extension, which is the bleeding edge code still uses ‘window.mozCipher’ as the window property name. The Firefox patch uses ‘window.mozCrypto’, the plan is to eventually merge this API into window.crypto )

I tried to make this API as simple as possible:

Encryption:

window.mozCipher.sym.encrypt(plainText, function callback(aCryptoObject){})

The resulting ‘CryptoObject’ has the following properties:

{
  cipherText: "...ENCRYPTED TEXT...",
  wrappedKey: "...A WRAPPED SYMMETRIC KEY...",
  iv:         "...KEY INITIALIZATION VECTOR...",
  pubKey:     "...A PUBLIC KEY..." // By default this pubKey
                                   // is the current user's public key,
                                   // which is used to wrap the symmetric key
                                   // so the actual key is never exposed to content.
}

Decryption:

window.mozCipher.sym.decrypt(aCryptoObject);

You can also pass in a public key to each method to wrap the key with another user’s key

Internally, a symmetric key is generated each time you run encrypt, it is wrapped with a public key to keep it safe and that cryptoObject is returned.

This is a first pass on an implementation – I tried to make it as simple as possible, with key safety the top priority.

A common use case for this API is localStorage encryption:

// web-based password manager app:)

var myWebPasswords = {gmail: "password", facebook: "password", twitter: "password"};

var jsonPasswords = JSON.stringify(myWebPasswords);

window.mozCipher.sym.encrypt(jsonPasswords, function callback(aCryptoObject){
  var jsonCryptPasswords = JSON.stringify(aCryptoObject);
  localStorage.setItem("jsonCryptPasswords", );
  delete myWebPasswords
});

// decrypt

var myWebPasswords;

var cryptoObj = JSON.parse(localStorage.getItem("jsonCryptPasswords"));

window.mozCipher.sym.decrypt(cryptoObj, function callback (aPlainText){
  myWebPasswords = JSON.parse(aPlainText);
});

This API is simple to use, and gives you a more secure way of using localStorage – or IndexDB, etc.