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Comment by IgorPartola | Hacker News Reader

The issue I have with LastPass is that they claim to never see your master password. This is not true in any sense. Open their website, log in using your master pass. You just submitted it to them. As a secondary thing, pick a random password from the list and say "Show me the password"; it will ask you for your master password. The extension you install has nothing to do with this: you are entering the password directly into their web page and interacting with their JavaScript and their server-side code. At this point they have your master password.

I understand why they do this: it's convenient and lets you share/give passwords to others. But this feature is 100% incompatible with the claim that they never see your master password.

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You are not submitting your master password to them. It's been a while since I completely understood the login process, but this should be mostly right:

1. The encryption key is a local hash of your email address and master password. This never leaves your computer.

2. Ignoring PBKDF2, Your encryption key and your master password are again hashed locally. That is sent with your login email to LastPass.

3. LastPass hashes Step 2 with a salt and that result is then used to authenticate you. After any additional two factor auth verification, LastPass will send your password file, which is decrypted using the result in Step 1, that has never left your computer.

You're more than welcome to inspect the JavaScript code yourself. They have a simple encryption, decryption page so you can see exactly what LastPass does.

https://lastpass.com/js/enc.php

My understanding is that even with their web login process your password isn't sent to their servers in plaintext. From the comments on their heartbleed blog post: "We only use one-way salted hashes (after going through PBKDF2 rounds) to send to the server for authentication."

So their servers get a hashed version of your password, but not the password itself. Their servers likely also store a hashed version of your password so that they can authenticate you. This style of auth is also used when you use the "show me the password" feature.

This cannot be. Your passwords (the ones you are trying to protect) must be encrypted using your master password. LastPass needs to decrypt them somewhere using your master password. What you are describing is how their browser extension seems to work. However, their website does not require the extension to work. So either they implement security in JavaScript that's running within the page (cannot by definition be done securely), or they store all your passwords in a way that they can decrypt them (invalidates the use case for LastPass).

We implement everything in JavaScript on that page if you're trying to login from the website -- which is as secure as that page load -- LastPass recommends people utilize the extensions to mitigate this risk.

Our choice could be to not allow people to utilize the website but it seems like educating people of the risks and letting them decide is the best policy.

Very happy to get a reply from someone from LastPass!

So then what would prevent someone from using the Heartbleed attack to obtain your private key that use used to secure the HTTPS connection from me to your servers, then inject malicious JavaScript into the page where I enter my password? This is the attack I am worried about outside of Heartbleed as well, since any CA can issue a valid certificate for lastpass.com and I would not know that I am being MITM'ed.

From a strict security point of view, disabling website access seems like the best policy. From a usability standpoint, I understand the tradeoff you made. Perhaps an option at the account level that disabled website access might be a good idea.

Also, how are the share/give functions handled? I know what "share" is not really keeping my password from being seen by the other person (there are a variety of techniques they can use to get at it), but how is the encryption handled on your end?

Lastly, how do I know that the browser extension I download from you is secure? Is there a way for me to verify it somehow?

Having said all that, I absolutely love your product and recommend it to everyone I know. It's a huge net win in terms of security.

The passwords are decrypted locally on your machine using javascript not on the lastpass servers.

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