All over the net, a huge number of sites offer you the option of E-mailing you your password if you have forgotten it. While this seems to make sense, it is actually a dreadful security policy, and if you see it, you should complain and point them to this article or others to get them to stop. As an alternate, they should at most offer to E-mail you a new, randomly chosen temporary password, which you can use to log in and set a more memorable password.

If a site can mail you your password, it means they are keeping a copy of it. They should not be doing that. First of all, almost everybody re-uses passwords at different sites. That means if one site has a security breach — as Convio did this week for a wide variety of sites that are its clients — your password will be stolen, and it can then be used on all the other sites you use it at. (This is a good reason to always use more protected, less duplicated passwords on sites where actual damage can be done or money can be spent, like banks, eBay, paypal etc.)

Instead, they should keep a “hash” of your password. A hash is a one way function. Given the plain password, they can hash it, and store the result, but you can’t get the plain password back from the hash. So you can check to see if a password that was typed matches the password without storing what the password is. This is actually a very easy thing to do in most systems, and its main downside is the fact that they can no longer e-mail you your password. They can, however, set it to something random and mail you that. That’s a touch more work in the rare event of a lost password, but worth the trouble.

There is, oddly, one minor downside to hashed passwords. With hashed passwords, you must provide the site your real password, and they can then test it and forget it. You must trust them to forget it. The real password, however, is sent over the internet and if you don’t use an encrypted channel, like SSL/TLS/https, it could be intercepted by people tapping the line. Some password systems (included the less commonly used HTTP password system) have the browser hash the password (in a special way that is different every time) and send the hash to log in. In this case, the real password is not sent, and can’t be sniffed, but must be in storage at the remote site. However, if you use an encrypted channel (https), there is no worry about the password going over the internet, and so there’s no reason not to do it that way.

There is a better way to do all of this. With digital signature, you can prove that you’re you using a secret private key only you know. Nobody else ever gets this key, and nobody can figure it out by watching the communications you send. While this technology has been around for some time, and is in fact implemented in most browsers (though far from perfectly) it is not a common way to authenticate to web sites at all.

However, next time a site offers to E-mail your password, point them to the Convio data theft and to this page and ask them to get their act together.