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[liberationtech] pgp message encryption and decrypion using just a browser

Anders Sundman sundman.anders at gmail.com
Thu Feb 10 01:17:18 PST 2011


Great project! I hope you get a lot of useful feedback from people on
this list and elsewhere.

Since your threat model seems to be based around a remote attacker,
this might not be entirely relevant; but extending the threat model to
an attacker with access to the computer that the browser is running on
seems like a logical next step.

In that case you will have to struggle with a common problem with any
type of crypto application. How to store the passphrase / priv.key in
a way that makes it as hard as possible for an attacker with access to
the computer to recover that data.

In the function:

function decrypt()
{
  var cryptoObj = {
    privKey: window.crypt.privKey,
    passphrase: document.getElementById("passphrase").value,
    aSalt: window.crypt.salt,
    aIV: window.crypt.iv
  };
  var decrypted =
    window.crypt.decrypt(document.currentMessage,
window.crypt.pubKey,cryptoObj);
  document.getElementById("decrypted").innerHTML = decrypted;
}

you call: decrypt: function DAPI_decrypt(aMsg, aPubKey, aCryptoObj) { [...]

This will off course put the privkey + passphrase in memory (there's
really no way around that). I'm no JavaScript expert so I might be
dead wrong here, but since JS is garbage collected, the cryptoObj
won't be destroyed right away (and the sensitive data will linger in
RAM longer that necessary). Setting the privKey/passphrase = 0 after
the decrypt call won't solve the problem entirely, but at least
tighten the vulnerable time frame. This will also make the risk of the
data getting paged to disc smaller (but won't eliminate it). I'm not
sure how Firefox handles the decrypted document once it's displayed,
but you would probably want to look in to stuff like caching, etc..
The torbutton design doc might com in handy:
https://www.torproject.org/torbutton/en/design/#id2934378

All the best,
Anders


On Wed, Feb 9, 2011 at 12:48 AM, David Dahl <david at ddahl.com> wrote:
> I have been wanting to follow up on this thread, which means writing
> some code.:)
>
> I have distilled the 3 methods needed to construct any kind of
> PGP-like web application. My new extension, DOMCrypt, attaches a
> 'crypt' property to each web page giving Javascript developers
> crypt.generateKeyPair(), crypt.encrypt() and crypt.decrypt().
>
> All of the underlying crypto code is handled by NSS - the same library
> used for the SSL/HTTPS. This is not a 'native JS' solution. It is fast
> C code under the hood.
>
> See http://mozilla.ddahl.com/domcrypt/demo.html for a demo, the code
> is here: https://github.com/daviddahl/domcrypt
>
> Regards,
>
> David
>
> On Sun, Sep 26, 2010 at 6:21 AM, David Dahl <david at ddahl.com> wrote:
>> I have been experimenting with the JavaScript API for PKI that is
>> provided by Firefox Sync. The underlying bits are implemented in C++
>> (NSS), so it is pretty fast. I am slowly building up a toolkit for
>> messaging in a pseudo-anonymous fashion called "Droplettr" and am
>> looking for contributors. The entire thing is open source and is
>> designed to be  used like a protocol instead of a walled garden.
>>
>> Repo: http://bitbucket.org/daviddahl/droplettr/
>>
>> Site: https://droplettr.com/
>>
>> Things are in a state of brokenness at the moment, as this is a side
>> research project of mine.
>>
>> Regards,
>>
>> David
>>
>> On Sat, Sep 25, 2010 at 12:00 AM, Danny O'Brien <DObrien at cpj.org> wrote:
>>> This really isn't what you want Frank (at all!), but its bizarreness plus tangential connection to your question was too good to miss:
>>>
>>> http://www.links.org/?p=993
>>>
>>> It's TLS (including client-side certificates), re-implemented in in-browser Javascript. Ben's point is that such an implementation allows greater experimentation with security UI, which I think everyone agrees is the current Hard Problem.
>>>
>>> d.
>>>
>>> On Sep 23, 2010, at 11:08 PM, Frank Corrigan wrote:
>>>
>>>> For some time I have been investigating the availability of web pages
>>>> that provide easy to use password creation and message encryption
>>>> functions, which only depend upon web browsers inbuilt javascript
>>>> capabilities and can therefore be downloaded and used off line. And
>>>> works across all common OSs and browsers.
>>>>
>>>> Examples are
>>>> https://www.pwdhash.com
>>>> as one of many options for password creation
>>>>
>>>> and http://www.hanewin.net/encrypt/PGcrypt.htm
>>>> to encrypt messages using a recipients pgp Public key.
>>>>
>>>> The help I am requesting is whether anyone knows of an online resource,
>>>> that meets the above criteria, that can not only encrypt text using a
>>>> pgp Public key but also has a facility to decrypt a pgp message with the
>>>> recipients Private key?
>>>>
>>>> I am aware of FireGPG:
>>>> http://getfiregpg.org/s/home
>>>>
>>>> which is excellent, though sadly now discontinued, but it is tied to
>>>> Fire Fox through an add-on and it's functions are dependent upon a local
>>>> install of GPG.
>>>>
>>>> Thanks
>>>> Frank
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