[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Cryptography] Possible reason why password usage rules are such a mess

On 11/19/20 2:46 AM, Phillip Hallam-Baker wrote:
Sure, nobody leaves the front door open on the password file any more. But breaches occur regularly and the password files leak...

You are optimizing for a very specific case:

(1) A site uses password hashes,
(2) for passwords that are allowed to be long,
(3) and are honored in their entire length*,
(4) is broken into and they don't tell me,
(5) the breakin doesn't include general admin powers but just supplies that one file,
(6) the attacker bothers to crack the hash for my password, and
(7) it does any good for the attacker to have that password.

* Even Linux is willing to let you use long passwords where anything past 8-characters are quietly ignored—if you set things up wrong. I've twice discovered this where I didn't set it up that way, a system installation script did.

If I don't recycle passwords, getting all the way to #7 lets the attacker impersonate me only on this one iffy site, which the attacker already has some backdoor access to. By insisting on unmanageably long passwords for everything, you do avoid this one narrow circumstance.

But there are a lot of ways for people to get security wrong, by the time they let their password data leak you need to assume things are very broken.

What makes you think there is any hashing going on at random site?

I have a large collection of plain-text passwords that have publicly leaked, where did I get those? That doesn't smell like hashing to me. Why do so many sites have password length and severe password content restrictions? That doesn't smell like hashing to me.

As long as my password even approaches a couple dozen-ish bits of real entropy, if I haven't given away copies (by recycling), my password is not going to be the weak link.

Do you have an ATM card? Well, if someone finds a way into your bank's computers that isn't via your PIN, then it didn't happen because your PIN was too short. And if you have to change your PIN as part of the cleanup, your new one doesn't have to be any longer than was your old one. The PIN wasn't the problem.

By telling people that every password has to be unmanageably long, you are effectively discouraging people from using difficult passphrases when it really does matter: for encryption.


The cryptography mailing list
cryptography AT metzdowd.com