Re: [lamps] draft-ietf-lamps-lightweight-cmp-profile-05 concern

"Brockhaus, Hendrik" <hendrik.brockhaus@siemens.com> Tue, 16 March 2021 17:43 UTC

From: "Brockhaus, Hendrik" <hendrik.brockhaus@siemens.com>
To: Nick Lamb <njl@tlrmx.org>
CC: "spasm@ietf.org" <spasm@ietf.org>, "steffen.fries@siemens.com" <steffen.fries@siemens.com>
Thread-Topic: draft-ietf-lamps-lightweight-cmp-profile-05 concern
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Archived-At: <https://mailarchive.ietf.org/arch/msg/spasm/ay6PFnzk0xLRrH_SmPVwhgmwB3g>
Subject: Re: [lamps] draft-ietf-lamps-lightweight-cmp-profile-05 concern
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Nick

Many thanks for your feedback. 

> Von: Nick Lamb <njl@tlrmx.org>
>
> I noted with concern that the presenter suggests TLS 1.3's PSK modes are
> suitable for use with a password.
> 
> This is _explicitly_ not the case. To quote RFC 8446:
> 
> "Deriving a shared secret from a password or other low-entropy sources is not
> secure.  A low-entropy secret, or password, is subject to dictionary attacks
> based on the PSK binder.  The specified PSK authentication is not a strong
> password-based authenticated key exchange even when used with Diffie-
> Hellman key establishment."

I am aware that passwords with low entropy will only result in shared keys with low entropy.

> If CMP or LAMPS generally needs a way to use passwords to authenticate TLS
> it's worth reaching out to the TLS WG to ask them what you should do here, or
> contrariwise if this profile for CMP is to use PSKs it should likewise make explicit
> that you must not use passwords and similar human memorable low-entropy
> secrets.

Finally using shared secret information, e.g., OTPs or passwords is definitely not the main line for protection of CMP messages.
Also, TLS is not the only protection, but an additional layer for CMP, as CMP offers object level security.
When using shared secret information for protecting CMP message integrity we move from the old password-based MAC mechanism specified in RFC 4210 and RFC 4211 to PBMAC1 to improve the security here. Russ submitted the draft for updating RFC 4211 in this regard (draft-ietf-lamps-crmf-update-algs) and I did the same for RFC 4210  (draft-ietf-lamps-cmp-updates, draft-ietf-lamps-cmp-algorithms).

I struggled to provide some guidance on which cypher suites to use with shared secret information together with TLS in the Lightweight CMP Profile as presented during IETF 110.
One option is also to drop these recommendation, if there is no adequate cypher suite to be used with shared secret information and TLS 1.3, as TLS is not required for protecting CMP messages.

Any recommendations are welcome.

Hendrik

Re: [lamps] draft-ietf-lamps-lightweight-cmp-prof… Brockhaus, Hendrik