Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Passkeys will come at a cost

fy.blackhats.net.au

Post reply on HN
Print view View original

31–40 of 600 posts

Re: Passkeys will come at a cost

#31

Post by dcow »

I think the author is taking the argument too far and also not being precise in their language which is the exactly the "passkey hype" they fault Apple and "Fido" for doing. Maybe just cut the exposition out of the article I don't think it helps the argument and makes the author sound angsty rather than contribute to the well thought out considerations towards the end. Point being, I think there's a point but it was hard to get there.

Anyway:

1. Passkeys, to me, are the private key. It doesn't matter whether it's resident or not, or whether it's device bound (non-extractable) or not, whether a "genuine" authenticator made the signature or not, or whether user presence was verified or not. A Passkey is not the authenticator/library as the author claims, and it's not the protocol or some set of protocol features.

2. The world is better off if everyone uses WebAuthN instead of passwords irrespective of how the passkey is stored. Full stop. So let's start there. Additionally, where I diverge from the author, I don't think preserving the sanctity of decade old hardware keys which only conform to older versions of a TPM spec is of paramount concern, either. The author's fixation on that is a little strong, but it's understandable.

3. I don't think you need to discourage resident keys. But I also don't think RPs need to care about whether the key is resident or not. Let the library on the user's browser/device decide how to find the key. An RP wanting to verify user presence is one thing, but saying this key must be stored with the user IMO is a step too far. It's likely that RPs don't even care and are just avoiding wanting to store some extra bytes in their DB. Or their security team overly cares and is making up reasons why the RP needs to require resident keys (IMO bad security take all things considered) but I can see the tin-foil angle).

So I think the simple solution is probably to, for WebAuthN specifically, deprecate the ability for the RP to specify that it needs a resident key. Problem solved.

Oh and while we're at it, forbid hardware attestation. The web doesn't need that. If rk=required and hardware attestation need to exist for tightly controlled enterprise use cases then whatever, but relegate them there preferably in some non-required protocol extension.

Re: Passkeys will come at a cost

#32

Post by kccqzy »

goalieca wrote: post #25

A private key for curve p256 is 32-bytes. Let's say we have associated metadata (hostname, whatever) and round that up to 1KiB per key. A typical user has around 200 accounts but let's give room for 1000 since powerusers love hardware keys. That's 1000 x 1KiB = 1MiB. This is totally within our technical capabilities. It's not uncommon for small radio coprocessors to have more storage on die. Even old school SIM cards…

You aren't buying a USB mass storage device when buying a security key. Completely different product, different requirements.

Re: Passkeys will come at a cost

#33

Post by the_snooze »

Ajedi32 wrote: post #27

Is it even a good idea to use physical security keys as passkeys in the first place? Passkeys are meant to be a password _replacement_, and for that you probably want the 2-factor properties afforded by phones or desktops which usually require "something you know" or "something you are" to unlock in addition to the "something you have" afforded by physically possessing them. IMO physical security keys are better left…

When I use a Yubikey for passwordless authentication (FIDO2), it challenges me for a PIN before asking me to touch the device. If I give it too many incorrect PINs, the Yubikey locks up and requires a device reset, which invalidates all previous registrations to use that key for authentication. It doesn't seem like a big deal if someone steals my hardware token.

https://support.yubico.com/hc/en-us/articles/4402836718866-U...

Re: Passkeys will come at a cost

#34

Post by jabbany »

I wonder if there could be a middle-ground software solution here?

E.g. A piece of software (like a passkey manager or keychain service) that transparently simulates a resident key store by using an encrypted database that resolves services to credential IDs which are then forwarded and unlocked by a non-resident hardware key. One could then conceivably still sync the database around (using whatever services or method you want), and even if the encryption of the database were somehow broken, it wouldn't be the end of the world, as the actual signing is still done by the hardware key.

(Disclaimer: I don't know enough about the actual protocols to judge if the above is actually technically feasible, but would be curious if it is)

Re: Passkeys will come at a cost

#35

Post by 0cf8612b2e1e »

dathinab wrote: post #26
saulrh wrote: post #2

That's a rather uncharitable take on the situation. I'll propose an alternative: If you want to take advantage of the new auth standard that will eliminate weak passwords and password reuse (thereby preventing 99% of casual account break-ins), you'll have to spend $30 to upgrade off the legacy yubikey you've been coasting on since 2013.

I would go as far and say it's a too charitable take. Shared residual keys _should not exist_ (outside of short term temporary usage, e.g. not 2FA/FIDO). They are a liability, they are a security risk, they promote bad security practices. Best example TOTP (which from a security POV is quite flawed). You don't want to ever share the shared secret across devices (or back it up) but due to it being possible and flawed…

> You don't want to ever share the shared secret across devices (or back it up)

Hard disagree there. I do not feel comfortable unless I can backup a key. Phones get lost/broken/stolen all the time. Is it less theoretically secure? Sure, whatever, but I am not James Bond.

Re: Passkeys will come at a cost

#36

Post by ericjmorey »

taeric wrote: post #13
conradev wrote: post #7

Earlier quoted context omitted.

Password managers can store passkeys. I plan on storing passkeys in a password manager for most accounts, and then moving the few that matter to be resident keys. The theoretical advantage here is twofold: - Passwords are not guessable any longer - Password managers don't expose secret material in normal operation, because they sign requests with keys stored in TEEs (i.e. most modern devices have an embedded security…

If passkeys become defined as resident keys, is this still true? And if this is acceptable, honestly, do we need a new standard? Password managers exist today. Such that I already do what you are suggesting here with passwords. Does it really become much more secure by the move to passkeys?

Passkeys are for the people that don't even use password managers outside of what Apple or chrome provides by default if at all. Passkeys are trying to eliminate those ad hoc solutions by providing a different system. The transition will be slow and messy requiring most people to use passkeys and passwords (and maybe password managers) for a while.

Re: Passkeys will come at a cost

#38

Post by politelemon »

Ajedi32 wrote: post #27

Is it even a good idea to use physical security keys as passkeys in the first place? Passkeys are meant to be a password _replacement_, and for that you probably want the 2-factor properties afforded by phones or desktops which usually require "something you know" or "something you are" to unlock in addition to the "something you have" afforded by physically possessing them. IMO physical security keys are better left…

I don't see phones as being very different in terms of also being a physical security key.

Re: Passkeys will come at a cost

#39

Post by prophesi »

politelemon wrote: post #38
Ajedi32 wrote: post #27

Is it even a good idea to use physical security keys as passkeys in the first place? Passkeys are meant to be a password _replacement_, and for that you probably want the 2-factor properties afforded by phones or desktops which usually require "something you know" or "something you are" to unlock in addition to the "something you have" afforded by physically possessing them. IMO physical security keys are better left…

I don't see phones as being very different in terms of also being a physical security key.

I think the key (pun not intended) differences are that phones are something you'll always have on your person, Apple/Google will allow it to sync across devices, and phones require a pin/biometrics to authenticate with them.

Re: Passkeys will come at a cost

#40

Post by matthewaveryusa »

Is this really how resident keys work? I thought the common use of all secure enclaves is to save keys outside the enclave, but symmetrically encrypted with a master key in the enclave, bypassing the memory limits. I can see the downside for yubikeys/usb enclaves being the keys are then no longer accessible, but for embedded enclaves this should never be a problem.
Post reply on HN