Re: [therightkey] [cabfpub] Thoughts on reducing SCT sizes (was Re: Updated Certificate Transparency + Extended Validation plan)
Ben Laurie <benl@google.com> Tue, 18 February 2014 15:30 UTC
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Date: Tue, 18 Feb 2014 15:29:52 +0000
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From: Ben Laurie <benl@google.com>
To: "certificate-transparency@googlegroups.com" <certificate-transparency@googlegroups.com>
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Cc: "therightkey@ietf.org" <therightkey@ietf.org>, Rob Stradling <rob.stradling@comodo.com>, CABFPub <public@cabforum.org>
Subject: Re: [therightkey] [cabfpub] Thoughts on reducing SCT sizes (was Re: Updated Certificate Transparency + Extended Validation plan)
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Sorry for long delay. On 5 February 2014 16:19, Jeremy Rowley <jeremy.rowley@digicert.com> wrote: > Table 1 of the plan document said both 3 SCTs and 4 SCTs for 27 months. > Until there is clarification on which is required, 3-4 is the best > representation of the requirement. I'm hoping Ben meant 15-27 months = 3 and > 27 = 4, but it's not clear from the document. Yes, that's exactly what I meant. > > Jeremy > > -----Original Message----- > From: public-bounces@cabforum.org [mailto:public-bounces@cabforum.org] On > Behalf Of Rob Stradling > Sent: Wednesday, February 05, 2014 5:37 AM > To: certificate-transparency@googlegroups.com > Cc: therightkey@ietf.org; CABFPub > Subject: [cabfpub] Thoughts on reducing SCT sizes (was Re: Updated > Certificate Transparency + Extended Validation plan) > > On Tue, Feb 4, 2014 at 12:33 PM, Jeremy Rowley wrote: >> Three or four proofs for a 27 month certificate is way too many. > <snip> >> Adding 400 bytes per certificate will make EV certificates unusable by > entities concerned with performance. > > The updated CT+EV plan requires three SCTs for a (maximum length) 27-month > EV certificate, not four. 400 bytes for three SCTs is about right though. > > Assuming RFC6962-compliant v1 SCTs that contain no SCT extensions and are > signed using ECDSA and a P-256 private key, then, including all of the ASN.1 > fluff for the SCT List certificate extension, I calculate that it'll be... > > 140 or 141 bytes to embed 1 SCT > > 261 to 263 bytes to embed 2 SCTs > > 380 to 383 bytes to embed 3 SCTs > > For (non-EV) validity periods between 27 and 39 months: > 499 to 503 bytes to embed 4 SCTs > > On 04/02/14 17:52, Adam Langley wrote: > <snip> >> We should make the SCTs as small as possible > > Agreed. Time for some back-of-an-envelope sums. For SCT v2, if we were to > pack in the data as tightly as possible I reckon we could cut it down to as > little as... > > 84 bytes to embed 1 SCT > > 159 bytes to embed 2 SCTs > > 231 bytes to embed 3 SCTs > > 303 bytes to embed 4 SCTs > > Here's how... > > 1. Use a shorter OID for the SCT List extension. Perhaps CABForum could > define 2.23.140.n (with n < 128). Save 6 bytes. > > 2. The first 2 bytes of the SignedCertificateTimestampList structure are its > total length. Since this can be calculated from the OCTET STRING length, > these 2 bytes could be omitted. Save 2 bytes. > > 3. Pack the SCT fields into as few bytes as possible for the common case, > whilst retaining options for future expansion. Save 37 bytes per SCT. > Replace... > (1 byte) Version sct_version; > (32 bytes) LogID id; > (8 bytes) uint64 timestamp; > (2+? bytes) CtExtensions extensions; > ...with... > (2 bits) sct_version (00=v1; 01=v2; 10,11=unassigned) > (2 bits) log_id_type (00=SHA-256(log_public_key); > 01=1-byte Registered Log ID; > 10=2-byte Registered Log ID; > 11=4-byte Registered Log ID) > (2 bits) timestamp_size (00=8-bytes; > 01=6-bytes; > 10=5-bytes; > 11=4-bytes) > (1 bit) extensions (0=CtExtensions is present; > 1=CtExtensions is absent) > (1 bit) signature_type (0=digitally-signed struct; > 1=raw Ed25519 signature) > For the common case: > (1 byte) Registered Log ID > (4 bytes) Timestamp (seconds, not milliseconds) > > 4. Use the Ed25519 signature scheme instead of ECDSA. ECDSA signatures > using a P-256 key seem to be 72 or 73 bytes, whereas Ed25519 signatures are > 64 bytes. Save 8 or 9 bytes per SCT. > Also, for Ed25519, omit the 2 bytes containing the hash algorithm and > signature algorithm from the "digitally-signed struct" header. Save 2 bytes > per SCT. > > -- > Rob Stradling > Senior Research & Development Scientist > COMODO - Creating Trust Online > _______________________________________________ > Public mailing list > Public@cabforum.org > https://cabforum.org/mailman/listinfo/public > > -- > You received this message because you are subscribed to the Google Groups "certificate-transparency" group. > To unsubscribe from this group and stop receiving emails from it, send an email to certificate-transparency+unsubscribe@googlegroups.com. > For more options, visit https://groups.google.com/groups/opt_out.
- [therightkey] Updated Certificate Transparency + … Ben Laurie
- Re: [therightkey] [cabfpub] Updated Certificate T… Jeremy Rowley
- Re: [therightkey] [cabfpub] Updated Certificate T… Adam Langley
- Re: [therightkey] [cabfpub] Updated Certificate T… Ryan Sleevi
- Re: [therightkey] [cabfpub] Updated Certificate T… Jeremy Rowley
- Re: [therightkey] [cabfpub] Updated Certificate T… Adam Langley
- Re: [therightkey] [cabfpub] Updated Certificate T… Jeremy Rowley
- Re: [therightkey] [cabfpub] Updated Certificate T… Jeremy Rowley
- Re: [therightkey] [cabfpub] Updated Certificate T… Ryan Sleevi
- Re: [therightkey] [cabfpub] Updated Certificate T… Adam Langley
- Re: [therightkey] [cabfpub] Updated Certificate T… Adam Langley
- Re: [therightkey] [cabfpub] Updated Certificate T… Jeremy Rowley
- Re: [therightkey] [cabfpub] Updated Certificate T… Adam Langley
- Re: [therightkey] [cabfpub] Updated Certificate T… Jeremy Rowley
- Re: [therightkey] [cabfpub] Updated Certificate T… Adam Langley
- Re: [therightkey] [cabfpub] Updated Certificate T… Jeremy Rowley
- Re: [therightkey] [cabfpub] Updated Certificate T… Adam Langley
- Re: [therightkey] [cabfpub] Updated Certificate T… Ben Laurie
- Re: [therightkey] [cabfpub] Updated Certificate T… Ryan Sleevi
- Re: [therightkey] Updated Certificate Transparenc… Wayne Thayer
- Re: [therightkey] [cabfpub] Updated Certificate T… Ryan Sleevi
- Re: [therightkey] [cabfpub] Updated Certificate T… Wayne Thayer
- Re: [therightkey] [cabfpub] Updated Certificate T… Jeremy Rowley
- Re: [therightkey] [cabfpub] Updated Certificate T… Ryan Sleevi
- Re: [therightkey] [cabfpub] Updated Certificate T… Wayne Thayer
- Re: [therightkey] [cabfpub] Updated Certificate T… Ryan Sleevi
- Re: [therightkey] [cabfpub] Updated Certificate T… Wayne Thayer
- Re: [therightkey] [cabfpub] Updated Certificate T… Ryan Sleevi
- [therightkey] Thoughts on reducing SCT sizes (was… Rob Stradling
- Re: [therightkey] Updated Certificate Transparenc… Ben Laurie
- Re: [therightkey] [cabfpub] Updated Certificate T… Rob Stradling
- Re: [therightkey] EXTERNAL: Re: [cabfpub] Updated… Mehner, Carl
- Re: [therightkey] Updated Certificate Transparenc… Rob Stradling
- Re: [therightkey] Updated Certificate Transparenc… Adam Langley
- Re: [therightkey] [cabfpub] Thoughts on reducing … Jeremy Rowley
- Re: [therightkey] [cabfpub] Updated Certificate T… Jeremy Rowley
- Re: [therightkey] [cabfpub] Updated Certificate T… Jeremy Rowley
- Re: [therightkey] [cabfpub] Updated Certificate T… Jeremy Rowley
- Re: [therightkey] [cabfpub] Updated Certificate T… Carl Wallace
- Re: [therightkey] Updated Certificate Transparenc… Paul Hoffman
- Re: [therightkey] Updated Certificate Transparenc… Adam Langley
- Re: [therightkey] [cabfpub] Updated Certificate T… Rob Stradling
- Re: [therightkey] Updated Certificate Transparenc… Paul Hoffman
- Re: [therightkey] Updated Certificate Transparenc… Rob Stradling
- Re: [therightkey] [cabfpub] Updated Certificate T… Rob Stradling
- Re: [therightkey] Updated Certificate Transparenc… Rick Andrews
- Re: [therightkey] Updated Certificate Transparenc… Adam Langley
- Re: [therightkey] [cabfpub] Updated Certificate T… Ryan Sleevi
- Re: [therightkey] [cabfpub] Updated Certificate T… michal.proszkiewicz
- Re: [therightkey] Updated Certificate Transparenc… Ben Laurie
- Re: [therightkey] [cabfpub] Updated Certificate T… Ben Laurie
- Re: [therightkey] [cabfpub] Updated Certificate T… Ben Laurie
- Re: [therightkey] Updated Certificate Transparenc… Ben Laurie
- Re: [therightkey] [cabfpub] Updated Certificate T… Rob Stradling
- Re: [therightkey] [cabfpub] Updated Certificate T… Ben Laurie
- Re: [therightkey] [cabfpub] Updated Certificate T… Rob Stradling
- Re: [therightkey] Updated Certificate Transparenc… Rick Andrews
- Re: [therightkey] [cabfpub] Updated Certificate T… Chema López González
- Re: [therightkey] Updated Certificate Transparenc… Ben Laurie
- Re: [therightkey] [cabfpub] Updated Certificate T… kirk_hall@trendmicro.com
- Re: [therightkey] [cabfpub] Thoughts on reducing … Ben Laurie
- Re: [therightkey] [cabfpub] Thoughts on reducing … Tim Moses
- Re: [therightkey] [cabfpub] Thoughts on reducing … Ben Laurie
- Re: [therightkey] [cabfpub] Thoughts on reducing … Daniel Kahn Gillmor
- Re: [therightkey] [cabfpub] Thoughts on reducing … Ben Laurie
- Re: [therightkey] [cabfpub] Thoughts on reducing … Daniel Kahn Gillmor
- Re: [therightkey] [cabfpub] Updated Certificate T… Rob Stradling
- Re: [therightkey] [cabfpub] Updated Certificate T… i-barreira
- Re: [therightkey] [cabfpub] Updated Certificate T… Rob Stradling
- Re: [therightkey] [cabfpub] Updated Certificate T… Mat Caughron
- Re: [therightkey] [cabfpub] Updated Certificate T… Mat Caughron