PwdHash from Stanford – Generate Passwords by Hashing the URL

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The Common Password Problem.

Users tend to use a single password at many different web sites. By now there are several reported cases where attackers breaks into a low security site to retrieve thousands of username/password pairs and directly try them one by one at a high security e-commerce site such as eBay. As expected, this attack is remarkably effective.

A Simple Solution.

PwdHash is an browser extension that transparently converts a user’s password into a domain-specific password. The user can activate this hashing by choosing passwords that start with a special prefix (@@) or by pressing a special password key (F2). PwdHash automatically replaces the contents of these password fields with a one-way hash of the pair (password, domain-name).

As a result, the site only sees a domain-specific hash of the password, as opposed to the password itself. A break-in at a low security site exposes password hashes rather than an actual password. We emphasize that the hash function we use is public and can be computed on any machine which enables users to login to their web accounts from any machine in the world. Hashing is done using a Pseudo Random Function (PRF).

Phishing protection.

A major benefit of PwdHash is that it provides a defense against password phishing scams. In a phishing scam, users are directed to a spoof web site where they are asked to enter their username and password. SpoofGuard is a browser extension that alerts the user when a phishing page is encountered.

PwdHash complements SpoofGuard in defending users from phishng scams: using PwdHash the phisher only sees a hash of the password specific to the domain hosting the spoof page. This hash is useless at the site that the phisher intended to spoof.

You can find the PwdHash extension for Firefox here:

More info is available on the Stanford PwdHash site here:

Stanford PwdHash

Posted in: Countermeasures, Password Cracking, Security Software

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3 Responses to PwdHash from Stanford – Generate Passwords by Hashing the URL

  1. Stefan March 14, 2007 at 8:42 am #

    I’ve only had a quick glance at the project, but this sounds pretty similar to the password hasher Firefox extension. I didn’t dig into the cryptographic details (yet), so I can’t say which extensions is more secure (if there is any difference at all); what I like about “password hasher” is the possibility to create the site-specific hash via JavaScript only: PwdHash seems to submit the data entered to the PwdHash server for computation. Password Hasher offers a page (which you can put a a trusted copy on your homepage, for example) which does the hashing solely in JavaScript – so you don’t have to trust some web service.

  2. Stefan March 14, 2007 at 1:08 pm #

    Ok, an update – I wondered why the PwdHash tried to submit data to the server… my fault, or better to say: NoScript‘s fault ;) So both extensions offer the same functionality, they merely differ in the user interface. PwdHash uses MD5, Password Hasher SHA1 as hash function for the keyed hash.
    The extensions differ in the user interface; the passwords generated by PwdHash have a length depending on the length of the master secret, while Password Hasher allows to select a fixed length (beside some options for special chars, etc.). The PwdHash team published a paper, discussing several attack vectors.

  3. Darknet March 14, 2007 at 6:19 pm #

    Thanks for the info and update Stefan, we appreciate that.

    I’ll post something about Password Hasher as well so people have the option to choose which is better for them.