Re: [TLS] Call for consensus: Removing DHE-based 0-RTT
Wan-Teh Chang <wtc@google.com> Thu, 31 March 2016 01:42 UTC
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Date: Wed, 30 Mar 2016 18:41:58 -0700
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From: Wan-Teh Chang <wtc@google.com>
To: Eric Rescorla <ekr@rtfm.com>
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Subject: Re: [TLS] Call for consensus: Removing DHE-based 0-RTT
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Hi Eric, Thank you for the reply. On Tue, Mar 29, 2016 at 10:57 AM, Eric Rescorla <ekr@rtfm.com> wrote: > > On Tue, Mar 29, 2016 at 10:14 AM, Wan-Teh Chang <wtc@google.com> wrote: >> >> [...] I am curious to know how we concluded that 0-RTT PSK is simpler to >> implement. Did anyone implement both 0-RTT modes and can compare the >> difficulties? > > We have a prototype 0-RTT PSK implementation and have looked at but not yet > implemented 0-RTT DHE in NSS. Based on that, my sense is that the cost of > doing any 0-RTT is the bulk of the additional effort, but that if you have > PSK already, which you probably want for ordinary resumption, then the > incremental cost of 0-RTT with PSK is less than with DHE. By analyzing Sections 7.1 and 7.3 of draft-ietf-tls-tls13-12. I think I understand what you meant. For convenience I reproduce the table at the top of page 74: +-----------------+------------------------+------------------------+ | Key Exchange | Static Secret (SS) | Ephemeral Secret (ES) | +-----------------+------------------------+------------------------+ | (EC)DHE (full | Client ephemeral w/ | Client ephemeral w/ | | handshake) | server ephemeral | server ephemeral | | | | | | (EC)DHE (w/ | Client ephemeral w/ | Client ephemeral w/ | | 0-RTT) | server static | server ephemeral | | | | | | PSK | Pre-Shared Key | Pre-shared key | | | | | | PSK + (EC)DHE | Pre-Shared Key | Client ephemeral w/ | | | | server ephemeral | +-----------------+------------------------+------------------------+ In a PSK session resumption handshake, we always use the same (third) row, with or without 0-RTT. On the other hand, in a full handshake, without 0-RTT we use the first row, and with 0-RTT we use the second row. Is this what you meant? But if you already implemented the first row, which is a must, the incremental effort to implement the second row seems small -- you just need to use server static instead of server ephemeral for SS. Wan-Teh Chang
- [TLS] Call for consensus: Removing DHE-based 0-RTT Sean Turner
- Re: [TLS] Call for consensus: Removing DHE-based … Bill Cox
- Re: [TLS] Call for consensus: Removing DHE-based … Wan-Teh Chang
- Re: [TLS] Call for consensus: Removing DHE-based … Ryan Hamilton
- Re: [TLS] Call for consensus: Removing DHE-based … Eric Rescorla
- Re: [TLS] Call for consensus: Removing DHE-based … Ilari Liusvaara
- Re: [TLS] Call for consensus: Removing DHE-based … Wan-Teh Chang
- Re: [TLS] Call for consensus: Removing DHE-based … Martin Thomson
- Re: [TLS] Call for consensus: Removing DHE-based … Wan-Teh Chang
- Re: [TLS] Call for consensus: Removing DHE-based … Hannes Tschofenig
- Re: [TLS] Call for consensus: Removing DHE-based … Eric Rescorla
- Re: [TLS] Call for consensus: Removing DHE-based … Hannes Tschofenig
- Re: [TLS] Call for consensus: Removing DHE-based … Eric Rescorla
- Re: [TLS] Call for consensus: Removing DHE-based … Hannes Tschofenig
- Re: [TLS] Call for consensus: Removing DHE-based … Hugo Krawczyk
- Re: [TLS] Call for consensus: Removing DHE-based … Eric Rescorla
- Re: [TLS] Call for consensus: Removing DHE-based … Hugo Krawczyk
- Re: [TLS] Call for consensus: Removing DHE-based … Martin Thomson
- Re: [TLS] Call for consensus: Removing DHE-based … Joseph Salowey