Subject: Re: [Uta] What are the actual best practices in the TLS BCP

From: Peter Gutmann <[email-masked]>
Date: Fri, 20 Jun 2014 23:16:15 +0000

Trevor Freeman <[email-masked]> writes:

>Use of 3DES today for instance by no stretch of the imagination can be
>classed as a "best" practice.

Why not?  Or at least, we need to figure out what the requirements are for
"best practice", I think we can agree on some things that aren't (e.g. using
MD5, RC4, etc) but is using an unbroken algorithm with a 35+ year track record
really a bad thing?  Sure, its pretty slow, but as a cryptographer recently
commented to me, "you're unlikely to be surprised" when (or long after) you
deploy it.

>Can I suggest a taxonomy of identifying practices in the BCP which are either
>best, acceptable or minimal in the document.
>
>E.g.

That's not really a classification mechanism (although it may be a taxonomy),
it's more of a shopping list.  For example:

>*         if I negotiate TLS 1.2, with EC, PFS, AES GCM, then that would be a
>best practice

Why not DH+RSA and AES with EtM?  I can make a good argument for those (the
DLP-based cryptosystems are extremely vulnerable to implementation issues that
tend to make them leak their private key, ECDSA doesn't have RSA's nice
asymmetric properties that make it amenable to use on low-power clients, and
everything does RSA but not everything does ECDH/ECDSA).

Peter.

---

From: Watson Ladd <[email-masked]>
Date: Sat, 21 Jun 2014 07:42:10 -0300

> everything does RSA but not everything does ECDH/ECDSA).

Performance matters: many servers don't support DH+RSA for performance
reasons, requiring ECDH instead. If clients don't support it, the
fallback is to non-PFS suites.

Clients don't validate DH parameters, and there is no list to check
against, which needs to be fixed before we can recommend them.

Sincerely,
Watson Ladd
>
> Peter.
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