Cryptico.js - strong encryption system utilizing RSA and AES for javascript

http://cryptico.wwwtyro.net/

by genieyclo • 15 years ago

77 61 15 years ago

cryptico.wwwtyro.net

pwpwp• 15 years ago

I'm collecting JS cryptography tools here:

http://www.delicious.com/manuel/javascript+crypto

nbpoole2• 15 years ago

I managed to dig up a recent comment thread by tptacek that explains why JS crypto is a bad idea:

http://news.ycombinator.com/item?id=2855556

dan_manges2• 15 years ago

Here's an in depth blog post from Nate Lawson explaining why JS crypto is a bad idea:

http://rdist.root.org/2010/11/29/final-post-on-javascript-cr...

thinner7• 15 years ago

A comment from that post:

"actually, i think an honest look at the security/privacy mechanisms provided by today’s tools precisely describes a case where ‘a little better than awful’ would be preferred. my mother emailed me some bank account information just last week. there isn’t any exploit required there. security software experts have failed horribly to provide tools that actual living breathing human beings might use and this is why most of them have just given up and use hotmail.

i personally find it astounding that the kind of people who will deny this probably have an actual brand new credit card sitting in their unlocked mailbox and feel perfectly comfortable with this fact.

your information’s security is only as strong as it’s weakest link. this includes the locks on your home, your mailbox, and the granularity you shred your trash with."

quadhome• 15 years ago

I'll wait for the cryptographers to weigh in; but, it's in Javascript.. already a language that's going to be hard to Do It Right in. (The first third of the code is a BigInteger implementation)

Then, I looked to see if the standard constant-time comparisons were in there to resist timing attacks. No dice there.

So... cool. He put a nice wrapper on JSAES[1], jsSHA2[2] by way of webtoolkit.info[3], RSA and ECC in Javascript by Tom Wu[4], and seedrandom.js by David Bau[5].

But then then says it's "New BSD license"[6] when it should be GPL[7].

I didn't start this comment sound negative. But, I think a few things are important:

* Credit authors.

* Respect their licenses.

* Put a big fucking notice on top of your slick webpage: "FOR DEMONSTRATION PURPOSES ONLY-- NOT REAL CRYPTO"

[1] http://point-at-infinity.org/jsaes/ [2] http://anmar.eu.org/projects/jssha2/ [3] http://www.webtoolkit.info/javascript-sha256.html [4] http://www-cs-students.stanford.edu/~tjw/jsbn/ [5] http://davidbau.com/archives/2010/01/30/random_seeds_coded_h... [6] http://code.google.com/p/cryptico/ [7] http://code.google.com/p/cryptico/source/browse/trunk/aes.js

etrain• 15 years ago

He credits the authors in his doc, but agreed on the warning - I am not a cryptographer, but my knowledge of side-channel attacks has me pretty worried that the RSA implementation is not safe.

thinner7• 15 years ago

Does anything qualify as 'real crypto'? Every implementation will always and forever have weaknesses. I don't have a problem with someone putting together a package that makes it easy to do crypto stronger than rot13 - isn't that a step forward? We'd all like GPG/PGP easy in the browser with native code, but until then, what's wrong with an intermediate step that appears to be at least pretty good and fairly easy to use? Maybe it's not enough for organizing a coup, but for keeping your fantasy football strategies a secret - why not?

dan_manges2• 15 years ago

Code that has been written and/or audited by cryptographers would qualify as 'real crypto.' I don't think anybody has a problem with someone putting together this package; the only problem is with the lack of a proper notice that the code hasn't been audited.

mkup2• 15 years ago

This thing won't replace https anyway, because if transferred over http, Javascript code could be intercepted and modified by adversary before it reaches client browser and before it is actually executed.

And if this JS code is transferred over https, what's the point of it? Don't we already have crypto in this case?

macmac2• 15 years ago

Couldn't the client verify the integrity of the code against a published hash?

mkup2• 15 years ago

yes, but hash comparison operator will be executed on client side only if it wasn't stripped away along the path

tptacek16• 15 years ago

No! Very common misconception!

You cannot verify the integrity of a browser Javascript cryptosystem by checking a SHA2 hash of the Javascript file containing the crypto.

That's because any other piece of content, from Ajax requests and whatnot to, in many browsers, the CSS files, some of them cached and some of them loaded on the spot... any other piece of content that contributed to the page that hosts the crypto code can alter the runtime to trivially intercept secrets or fix keys.

Until browsers provide a primitive to verify the whole runtime, cryptographic hashes won't do anything to ensure integrity for Javascript.

ams6110• 15 years ago

Unless you are an expert cryptographer and write your own code from scratch, including the compiler and if you are really paranoid building your own hardware, you are always relying on third parties as your source for crypto code and the devices upon which it executes, and you have to trust they they have not inserted backdoors.

eli• 15 years ago

This is not an abstract, advanced threat like "someone backdoored your processor."

Javascript sent over the Internet in cleartext is trivial to intercept and alter.

Astrohacker• 15 years ago

Not all uses of cryptography are for encrypting information sent over a channel. Consider bitcoin, which uses public/private keys and hashing functions to create a digital currency. No encryption is even involved.

sneak2• 15 years ago

From the source:

    // For best results, put code like
    // <body onClick='rng_seed_time();' onKeyPress='rng_seed_time();'>
    // in your main HTML document.

And if one doesn't...

tptacek16• 15 years ago

I like the phrasing "for best results". "Cryptography. For best results, use random numbers."

(Ping me [see profile] if you want a sticker for finding that issue. They're neat!)

ctz• 15 years ago

An entertaining and original way of removing PKCS#1 signature padding:

  var hDigestInfo = biDecryptedSig.toString(16).replace(/^1f+00/, '');

(Just a pity the signature verification function is broken by it.)

moxie2• 15 years ago

There's an interesting problem that is still unsolved in this space. Most people want JS crypto so that webapps can provide "end to end" encryption, relieving participants from having to trust the webapp service with their plaintext. The problem is that trusting you get the correct JS from the webapp for every message you'd like to send is reducible to trusting the webapp with your plaintext.

I think there are probably some novel solutions to this problem, but it would require work to be done by the browsers.

tptacek16• 15 years ago

We seem to be on a track now such that in 5 years, all the mainstream browsers will support a set of crypto primitives built into the browser, implemented in C, and exposed via Javascript bindings. And that's fine.

But it means that we're not going to have end-to-end crypto in web applications for another ten years, because these schemes don't degrade gracefully; the majority of users will have to upgrade before they become useful.

moxie2• 15 years ago

And I'm not sure that this would be enough, either. Crypto primitives are nice, but you still have to trust the webapp to deliver JS which calls those primitives every time you visit the webapp. I believe that this is again reducible to trusting the webapp with your plaintext, since the webapp could selectively intercept any message it chooses.

peterbraden2• 15 years ago

5 years is eternity on the web. Unless browser crypto is pushed through faster, we're gonna see a lot more of these.

yuhong• 15 years ago

Yea, I know, IE in particular is quite infamous, and people has been saying that IE8 is the new IE6 for a while now.

tptacek16• 15 years ago

Even if this wasn't browser Javascript and thus totally boned, it think it would still be pretty boned. I'll send a neat looking laptop decal to anyone here who spots any of the flaws in this cryptosystem.

But it is written as browser Javascript and is thus totally boned. Here's my attempt to be exhaustive about why:

http://www.matasano.com/articles/javascript-cryptography/

nbpoole2• 15 years ago

OK, I'm having a lot of fun reading this.

One little nitpick:

> What systems programming functionality does Javascript lack?

Here's a starting point: a secure random number generator.

Chrome has actually implemented one (http://blog.chromium.org/2011/06/new-chromium-security-featu...). It's a part of WebKit (http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2011-Feb...).

Firefox has an unimplemented (as of Firefox 6) secure RNG API (https://developer.mozilla.org/en/JavaScript_crypto, https://bugzilla.mozilla.org/show_bug.cgi?id=440046).

JoshTriplett• 15 years ago

Off the top of my head, reasons why this appears broken even if it didn't use Javascript:

The passphrase almost certainly doesn't have 1024 bits of entropy in it, and since they describe it as "used to repeatably generate this RSA key", they can't have introduced any additional entropy. And indeed, they just use the SHA256 of the passphrase to seed a PRNG.

They claim that a PublicKeyID "can be used to uniquely identify Sam's public key". Fingerprints help identify keys more easily, but certainly not "uniquely" since they don't have as many bits as the key; pigeonhole principle.

Worse, the PublicKeyID uses MD5.

They use a public exponent of 3, rather than the usual 65537 or larger. It looks like they might protect against small-exponent attacks, but I don't have enough expertise to know that for certain, and in any case this seems like a bad idea.

Neither cryptico nor the rsa-sign library they use mentions anything about HMACs; I haven't dug into the code to figure out if they actually use one or just use a hash directly.

Probably piles more, but I stopped there. :)

tptacek16• 15 years ago

I don't think this code protects against even the e=3 broadcast attack, because it doesn't verify the padding (as someone downthread noticed; I owe him a sticker now too).

Of course, not verifying the padding also means the signatures are straightforward to forge.

(Ping me with a shipping address and I'll send you swag).

cipherpunk4• 15 years ago

Are they suggesting to use the same RSA key for encryption and signing?

tptacek16• 15 years ago

It doesn't look like it; maybe you spotted something I missed.

Raphael• 15 years ago

What about Web Workers? It seems that would isolate JS from several security holes.

tptacek16• 15 years ago

In what sense does "Web Workers" insulate cryptography from the hostility of the JS runtime?

peterbraden2• 15 years ago

Some thoughts:

- Writing crypto systems in dynamic languages is hard/impossible

- There is a need for browser based crypto

- The browser manufacturers are moving too slowly in this regard

tptacek16• 15 years ago

Writing crypto in dynamic languages is hard but not impossible. Writing crypto in dynamic languages with content-controlled code is probably impossible.

papaf• 15 years ago

There is a need for browser based crypto

I would love to see reasonably secure browser based crypto. You could submit things to a website without the website being able to see what they are.

Imagine a social network that was opaque to the people hosting the social network.

Cryptico.js - strong encryption system utilizing RSA and AES for javascript

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