The article has many points, but it seems that they can be grouped together around three themes:

1. very easy for MITM-type attacks: this is negated by using SSL

2. JavaScript is too "malleable" for crypto - this argument is not very clear; yes, JS is "malleable" - so what, if we can be reasonably sure it is not "infected", by using server-side tools like signatures and SSL? This is highly debatable...

3. server breaches easily propagate to users: this is a real issue, but it is a real issue with many products that auto-update themselves, such as OSes (with patches/updates), browsers, anti-viruses, etc. Thus although this is a valid concern, it is part of everyday life of most Internet users,and not something JS crypto is specifically bad at.

By "malleability", we mean that code loaded in the future can monkey patch away the random number generator or AES block cipher function. I'm pretty sure that isn't debatable.

You keep saying that you mitigate this problem by controlling your pages 100%. Congratulations, you have gone farther than many of the JS crypto apps I've looked at; many of those bug their pages with Google Analytics, or with Typekit.

But that doesn't mitigate the problem that your users can't police you. They are relying entirely on your promise not to deploy code that will surreptitiously defeat the security of AES (or whatever ciphers you're using). And because JS is malleable, it is untenably hard even for an expert to attempt to validate your code by hand.

In other words, "I don't understand #2, so let's assume it's not a problem and handwave it away." Alas, it is a problem, and a critical one. Pray tell, how do you check the VM, from inside the VM sandbox? Guess what: you have no way to do that, not in JavaScript. That's another chicken-and-egg problem which is insurmountable with client-side, in-page JS.

I cannot do that from inside the sandbox, but as I completely control the page, not just one script on it, I can be reasonably sure no rogue script is running on it (by using SSL).

I've read the Matasano article, don't assume I didn't. Most of the points in it are negated by controlling the page 100% and using SSL.

I'm confused. In way does your application protect users against you? You control the code that handles the users encryption secrets. Your users have no effective way to police you.

Why not just have the users send you their plaintext, and rely on SSL/TLS for the rest of your security? It seems like that provides effectively the same security.

This is no longer true. There exists the Stanford JavaScript Crypto Library authored by known experts, including Emily Stark, Mike Hamburg and Dan Boneh:

http://crypto.stanford.edu/sjcl/

I also suggest reading the paper that comes along with the library, addressing several of the common issues like randomness and entropy generation and integer calculations in JavaScript: http://crypto.stanford.edu/sjcl/acsac.pdf

Matasano refers to SJCL in his article, it does not invalidate many of his points. If you had read his article you would know that it cannot simply be 'no longer true'. The article shows fundamental problems with security on the web and in javascript.

The article assumes that the web service with JavaScript crypto is not using SSL. It explicitly says

"And if you have SSL, why do you need Javascript crypto? Just use the SSL."

aes.io uses SSL _and_ JS crypto on top of it to make sure server-side data is always encrypted, with keys unkown to the server side.

"aes.io uses SSL _and_ JS crypto on top of it to make sure server-side data is always encrypted, with keys unkown to the server side."

So, if I understood it correctly the keys are unknown to the server because they are encrypted locally by javascript code which is provided by the very same server. By doing that, aren't you implicitly trusting the server every time you download the JS crypto library from them and assuming they are actually not peeking?

In that scenario, you might as well upload the files without encryption and provide them with the keys (through SSL of course :) ), and still assume that they encrypt it in the server (without peeking) and delete your key plus temporary copy when done...

So how do I know you (aes.io) changed the JS to leak my password to you? I can never be sure without comparing the JS you send me to some JS I know to be secure.

disclaimer: I'm working on a client-side JS crypto web-app myself :P

That is true - if the server side is compromised, all bets are off. However, how this is different from, let's say, a compromised browser update?

And good luck with you app - client-side JS crypto needs more dev attention. :)

I'll tell you how it's different: because you, the server operator, can at any time compromise the user. But you could not have compromised the integrity of their browser.

Since the whole point of clientside encryption is to prevent the server from compromising data, the fact that the server retains the ability to do this almost defeats the purpose of encrypting.

There are two issues here, I think.

One is intentional leakage, or trusting the vendor to be "not evil". Here you are right - as you mentioned in another comment, there is no easy way for users to "police" the vendor of JS crypto. I do not see, however, how this is different from users trusting other vendors of auto-updating software.

You can probably argue that OSS pieces such as Linux and FF have this "policing" enabled through source code availability. But there are many closed-source vendors (Microsoft, Google, anti-virus vendors) that many users trust. If you don't trust the companies mentioned above, then yes, you should not trust aes.io and other JS-crypto based vendors. But if a user has Microsoft/Apple updates enabled, and browsers (other than FF) auto-updating on their systems, etc., then this becomes a question of vendor being "not evil", not weaknesses of JS crypto, and as such somewhat out of scope of scrictly "JS crypto - yes or no" discussion.

The second issue here are unintentional leaks and breaches. Read-only breaches, for example, become more or less non-issue with JS crypto, because stealing properly encrypted data is not that useful. And there are probably orders of magnitude more read-only breaches than read-write, simply because inside companies more people have read-only access to production data than read-write access. Thus JS crypto seems to help substantially reduce the risk of unintentional compromises.

The second issue needs more attention and discussion from the technical point of view, I agree, and I am open to it. The first issue, however, becomes "I trust this vendor but I don't trust that vendor", and this is not a discussion that I believe can be productive here and now.

You've moved the goalposts.

You ask people to use your service because it is more trustworthy than others because it uses (presumably) AES encryption.

Then, when it's pointed out that your service is no more secure than any other service, in that all these services rely entirely on a promise by their operators not to breach privacy, you say "well that's no worse than any other service".

Now, I think there are a bunch of ways in which services like this are worse than other services. But I don't think I need to make that case, because, more importantly, they're not any better.

Bzzzt, strawman argument! You have addressed one point out of approximately 10 in the article and you are apparently assuming that it renders the remaining issues invalid. It doesn't.

Did you actually read the SJCL page before you wrote this comment? Because it rebuts you.

Even though client-side JS has some fundamentally insecure properties it does not mean it can't be used for establishing reasonably secure communication. HTTPS suffers from some of those properties too and we rely on https for almost everything we do that requires some sort of security.

If your site is entirely self-contained and transported in full over https with a trustable ssl certificate and your users are using reasonably secure passwords and run browsers with addons that respect the confidentiality of https communication then client-side js encryption might be a nice extra layer of data protection.

It won't protect against the government probing, and it won't protect against a passionate lulz hacker.

The government can always subpoena the host website, and force it to fetch the password from the user, thereby comprimising their data. The government also has access to ssl certificates so it could even do this without notifying the host website. You may assume that lulz hackers have similar capabilities.

If you think about it straight, the only way this can be truly secure is with a browser extension that digitally signs and versions _all_ javascript on a website, and the signing is done by a fully trusted third party (which arguably don't exist).

There is one thing client side js does protect you against very well and that is simple sql-injection style vulnerabilities.

Any database exposure vulnerability that does not compromise the host is fully mitigated by client side encryption. This is a very large class of vulnerabilities in the real world, so this is actually a very good case in favor of client side encryption.

Uh, what?

Losing the database is game over. The odds are very high that by losing the database loses command execution on the server.

Well that depends entirely on wether you've configured your environment securely. If your sql server runs as an unprivileged user preferably on a different machine this should not be an issue.

Even if someone were impressively thoughtful about that, they'd still cough up arbitrary code execution on the web tier for most Rails / Django applications, by writing an appropriately serialized external command into the queuing system. That external command would be loading metasploit into /tmp and then gaining root with a local privilege escalation.

Thomas is right, though: if you lose the DB, you're forked.

Uh huh.

So you obviously don't agree, care to elaborate? You seem to be the expert here..

(btw I don't mean that command execution is not a problem, I mean that if you configure your sql server well it should not allow command execution, there's not _that_ many ways to escape the database..)

This is one of those discussion where when I point out mistakes that (a) everyone makes and (b) you haven't thought of before and (c) are exploitable whether or not you encrypt, you're going to say "oh, well, you just shouldn't make those mistakes", and so I'm not interested in pursuing this and am content to rest my case.

>There is one thing client side js does protect you against very well and that is simple sql-injection style vulnerabilities.

Um, I don't think so. Client side JS is very good at doing SQLi. How on earth does client-side encryption mitigate against SQLi?