Re: [TLS] TLS 1.3 Recommended ECC curve for 192-bit security

[John Mattsson <[e-mail]>]

From: Michał Staruch <[e-mail]<mailto:[e-mail]>>
Date: Monday 12 October 2015 11:34
To: John Mattsson2 <[e-mail]<mailto:[e-mail]>>
Cc: "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>
Subject: Re: [TLS] TLS 1.3 Recommended ECC curve for 192-bit security

>We already have "SHOULD support key exchange with X25519" in this section,

Yes, but X25519 is also only providing 128-bit security (or 127.5).

>so people implementing it should have no problems with adopting X448<https://tools.ietf.org/html/draft-irtf-cfrg-curves-10#section-6.2> to achieve ~224 bit security where it's needed (and >better performance than P-384).

People will probably not have any problems adopting X448, P-384, or brainpoolP384r1. The problem is that different libraries may support different curves and start diverging. Stating SHOULD support for TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 without specifying a matching ECC curve is just half of what is needed for interoperability.

The sentence "These cipher suites SHOULD support both digital signatures and key exchange with X448.” would be equally good.

On Mon, Oct 12, 2015 at 11:01 AM, John Mattsson <[e-mail]<mailto:[e-mail]>> wrote:
I think the selection of MTI Cipher Suites (Section 8.1 of draft-ietf-tls-tls13-09) is excellent, but I am missing a recommended ECC curve for the “SHOULD” cipher suites. Little benefit of using AES-256 with P-256 or curve25519. Shouldn’t there be a SHOULD implement ECC curve giving at least 192-bit security? E.g.

"These cipher suites SHOULD support both digital signatures and key exchange with secp384r1 (NIST P-384)."

Cheers,
John


JOHN MATTSSON
MSc Engineering Physics, MSc Business Administration and Economics
Ericsson IETF Security Coordinator
Senior Researcher, Security

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