Mozilla Persona for the non-web | Hacker News Reader

Mozilla Persona for the non-web

hacks.mozilla.org

64 pointsrnyman16 comments

I recently investigated using Persona for a web service and mobile app that I am building. I think I will be using it. However there is one aspect that bugs me. I'm not very knowledgeable about crypto stuff so maybe someone else here can enlighten me.

The part that bugs me is that it seems to rely on clients keeping a private key secret and I'm not sure we can trust clients that are often programs downloaded off the internet to do so. What stops a maliciously coded BrowserID client from sending the user generated private key to a web service (the RP) along with the identity assertion?

Wouldn't this allow this malicious RP to login to other services that support Persona on the user's behalf and read and write info from his other accounts at least for the duration of the certificate?

This certainly wouldn't happen in the Mozilla implementation of the browserID client and I'm not sure it's a huge concern. Since the certificates are of short duration it's certainly not as bad as people using the same password across different services. And of course all single signin systems have risks when malicious services are involved such as the impersonation of the login page to get users to reveal their passwords but still, can someone put my mind at ease about this particular case?

Services should reject any "identity assertion" that claims to be for the wrong service, so having a malicious client log in to my LivingBook won't allow you to compromise my Twindr account. You can read more if you like: https://developer.mozilla.org/en-US/docs/Persona/Protocol_Ov...

Edit: Before I talked about some stuff that you obviously already knew :)

What I'm talking about here is a malicious service (Relying Party) that provides his own malicious BrowserID client to the user. Web services or mobile apps often provide their own clients. If the user's private key is leaked to a malicious RP when the user logs in this RP, can't it generate fake identity assertions (using the leaked key) to use along with the user certificate to login to any other Persona account? The faked identity assertion can claim to be for any service.

Ah, yes, a valid user certificate and the corresponding private key would allow you to impersonate the user for other RPs for the duration of the cert. That is troublesome.

Edited more: If you ship the user a malicious client and the user runs it, you can just keep his email password. This probably grants you access to all of his accounts for longer than the cert would last anyway. If the user uses 2-factor auth, the private key + cert combo is more useful than the password though.

Having a browser native client will help.

Persona, in some ways, seems to be filling the PKI gap.

It's a simple method for any email supplier to supply a key asserting that a particular email address is owned by a particular person, that that person can then use to authenticate elsewhere.

I'm actually somewhat baffled that it's taken this long for someone to come up with it!

Likewise. We want to extend it to non-web protocols where other attempts such as SPKM and PKU2U have either failed or not got much traction beyond a particular vendor implementation (respectively).

It's nice to know that this is being worked on. As a web app there are several ways to punt on managing user accounts (though some of them will earn you a lot of HN comments saying "I can't use it due to facebook auth"). It would be great to be able to do this for native apps as well.

Article author here. Many native apps of course will use HTTPS and will be able to use ordinary Persona. The protocol described in the article is for native applications that need replay detection, key exchange, mutual authentication, etc (particularly those that already use SASL and/or cannot use TLS).

The title sounded very promising. The "proof of identity" system we use in the "non-web" is very crude: Handwritten signatures are about the cheapest and most easily forged type of authentication you can think of, and yet they are (combined with your full name), usually legally valid and binding. A picture of someone holding up a purse with his driver's licence, back of a debit card, passport or identity card is all it takes.

But it turns out they mean "non-web" as in "ssh, imap, etc."

I keep waiting for someone to come up with something better than handwritten signatures; a (H)MAC of some sorts seems the way to go. It just doesn't come... And yes, I've also tried to devise my own system to cryptographically sign documents, but it's not practical yet. Basically you're converting the document to a digital format before generating a 128-bit signature (that you can then put on the paper as 16 Unicode characters), which is not really ideal.

I'm pretty sure that in most places, your signature is only legally binding when you are the one that signed it. It doesn't particularly provide authentication, but in cases of fraud it provides some evidence of intent.

Of course, but the signature is the proof that you are the one that signed it.

Im not sure how a signature could prove who signed it. Handwriting analysis can tell some things, but how many people still sign enough of a name to actually analyze. Look at the [Jack Lew signature](http://www.google.com/imgres?imgurl=http://images.politico.c...), assume that doesn't tell anyone much about _who_ signed it.

I don't think it is used that way very often.

Besides on every exam I've attended (school and for driver's license), and pretty much everywhere else where I had to prove my identity.

So for how many of your school exams do you think someone actually authenticated your signature? If it is never checked, it is reasonable to argue that it isn't being used to verify anything. Also, on things like exams, it is being used to encourage the test takers to take the honesty pledge seriously (and again, if someone signs a wrong name, it shows deceitful intent).

Identity is much more slippery than you are making it out to be. A signature doesn't prove it. An authentic government document doesn't prove it (it just verifies that you went through that particular identity verfication process).

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