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Comment by theCricketer | Hacker News Reader

For people that know more about web security than I: Is there a reason it isn't good practice to hash the password client side so that the backends only ever see the hashed password and there is no chance for such mistakes?

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Realize the point of hashing the password is to make sure the thing users send to you is different than the thing you store. You'll still have to hash the hashes again on your end, otherwise anyone who gets accessed to your stored passwords could use them to login.

But at least, with salt, it wouldn't be applicable to other sites, just one. Better to just never reuse a password though. Honestly sites should just standardize on a password changing protocol, that will go a long way towards making passwords actually disposable.

I don't think a password changing protocol would help make passwords disposable. Making people change passwords often will result in people reusing more passwords.

No the point is for password manager. The password manager would regularly reset all the password.... until someone accesses your password manager and locks you out of everything!

If by protocol you mean a standard, consistent API that can be used by password managers to update passwords automatically, then I completely agree.

In particular, the point is to make it so that the thing you store can't actually be used to authenticate -- only to verify. So if you're doing it right, the client can't just send the hash, because that wouldn't actually authenticate them.

Ultimately, what the client sends to the server to get a successful authentication _is_ effectively the password (whether that's reflected in the UI or not). So if you hash the password on the client side but not on the server, it's almost as bad as saving clear text passwords on the server.

You could hash it twice (once on the server once on the client) I suppose, but I'm not entirely sure what the benefit of that would be.

A benefit would be that under the sort of circumstance in the OP, assuming sites salted the input passwords, the hashes would need reversing in order to acquire the password and so reuse issues could be obviated. But I don't think that's really worth it when password managers are around.

I'm imagining we have a system where a client signs, and timestamps, a hash that's sent meaning old hashes wouldn't be accepted and reducing hash "replay" possibilities ... but now I'm amateurishly trying to design a crypto scheme ... never a good idea.

> meaning old hashes wouldn't be accepted and reducing hash "replay" possibilities

How would the server even verify the hash, then?

Verify the signature, check the time, use the hash as if it were the password to re-hash and compare with DB?

I think there is value in that. I would still be sure to hash it a second time on the server.

My guess is that this isn't popular because of the added client side complexity.

I'm also curious if anyone has considered or implemented this idea.

Ah answered elsewhere, if the client sends the hash and you log the hash then you still have a problem. The user should change passwords.

Although I think this still improves the situation if the password is reused. I.E. I can't use the logged hashed password on other sites.

Assuming that you are referring to browsers as client here. One simple reason is that the client side data can always be manipulated so it does not really makes any difference. It might just give a false sense of safety but does not changes much.

In case we are talking about multi-tier applications where probably LDAP or AD is used to store the credentials then the back end is the one responsible for doing the hashing.

I can't think of a good reason not to hash on the client side (in addition to doing a further hash on the server side -- you don't want the hash stored on the server to be able to be used to log in, in case the database of hashed passwords is leaked). The only thing a bit trickier is configuring the work factor so that it can be done in a reasonable amount of time on all devices that the user is likely to use.

Ideally all users would change their passwords to something completely different in the event of a leak. But realistically this just doesn't happen -- some users refuse to change their passwords, and others just change one character. If only the client-side hash is leaked rather than the raw password, you can greatly mitigate the damage by just changing the salt at the next login.

If you don’t have control on the client, it’s a bad idea: Your suggestion means the password would be the hash itself, and it wouldn’t be necessary for an attacker to know the password.

For one, you expose your hashing strategy. Not that security by obscurity is the goal; but there's no real benefit. Not logging the password is the better mitigation strategy.

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