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crypto/elliptic: carry bug in x86-64 P-256 #20040

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agl opened this issue Apr 19, 2017 · 12 comments
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crypto/elliptic: carry bug in x86-64 P-256 #20040

agl opened this issue Apr 19, 2017 · 12 comments
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FrozenDueToAge Security
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Go1.8.2

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@agl
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agl commented Apr 19, 2017

Cloudflare reported a carry bug in the P-256 implementation that they submitted for x86-64 in 7bacfc6. I can reproduce this via random testing against BoringSSL and, after applying the patch that they provided, can no longer do so, even after ~231 iterations.

This issue is not obviously exploitable, although we cannot rule out the possibility of someone managing to squeeze something through this hole. (It would be a cool paper.) Thus this should be treated as something to fix, but not something on fire, based on what we currently know.

Fix will be coming in just a second.
@agl agl self-assigned this Apr 19, 2017
@ianlancetaylor ianlancetaylor added this to the Go1.8.2 milestone Apr 19, 2017
@ianlancetaylor
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@agl This sounds like something we should fix in 1.8.2 and 1.9, but it is not necessary to release a new version of 1.6 or 1.7 with a fix. Does that sound right to you?

@agl
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agl commented Apr 19, 2017

I'm not very familiar with the convention for what gets backported and how far, but I agree that this is suitable for 1.8.2, certainly should be in 1.9 and it seems reasonable that it's not so important to warrant a respin for older versions, yes.

@ianlancetaylor
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Reopening for backport.

@gopherbot
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CL https://golang.org/cl/41070 mentions this issue.

@bradfitz bradfitz mentioned this issue May 18, 2017
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@gopherbot
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CL https://golang.org/cl/43770 mentions this issue.

@gopherbot
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CL https://golang.org/cl/43773 mentions this issue.

gopherbot pushed a commit that referenced this issue May 23, 2017
@agl @broady
[release-branch.go1.7] crypto/elliptic: fix carry bug in x86-64 P-256…
9a9b015 
… implementation.

Patch from Vlad Krasnov and confirmed to be under CLA.

Fixes #20040.

Change-Id: Ieb8436c4dcb6669a1620f1e0d257efd047b1b87c
Reviewed-on: https://go-review.googlesource.com/41070
Run-TryBot: Adam Langley <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>
(cherry picked from commit 9294fa2)
Reviewed-on: https://go-review.googlesource.com/43773
Run-TryBot: Brad Fitzpatrick <[email protected]>
Reviewed-by: Chris Broadfoot <[email protected]>
gopherbot pushed a commit that referenced this issue May 23, 2017
@agl @broady
[release-branch.go1.8] crypto/elliptic: fix carry bug in x86-64 P-256…
38d35f4 
… implementation.

Patch from Vlad Krasnov and confirmed to be under CLA.

Fixes #20040.

Change-Id: Ieb8436c4dcb6669a1620f1e0d257efd047b1b87c
Reviewed-on: https://go-review.googlesource.com/41070
Run-TryBot: Adam Langley <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>
(cherry picked from commit 9294fa2)
Reviewed-on: https://go-review.googlesource.com/43770
Run-TryBot: Brad Fitzpatrick <[email protected]>
Reviewed-by: Chris Broadfoot <[email protected]>
@agl
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agl commented May 23, 2017

(This issue is CVE-2017-8932.)

@pierrre
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pierrre commented May 23, 2017

I have a suggestion about the release note.
Maybe we should include a notice that strongly encourage to upgrade especially if net/http (or other package that require crypto/elliptic) is imported.

As an app developer, I don't use crypto/elliptic in my code.
However it's a package imported by package I use.

@FiloSottile
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FiloSottile commented May 23, 2017 via email

@broady
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broady commented May 24, 2017 •
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Announcement was sent before I read your comment, @FiloSottile, but yes... for those following along, agl's statement in the first post is still true for TLS (as used by net/http).

If you're using the elliptic package directly, such as working with JWTs, then you probably want to update. If you're not, then wait for Go 1.8.3, which should be released tomorrow.

@broady broady closed this as completed May 24, 2017
@cryptohazard
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Can someone please summarize what the issue actually means?
What are the odds of the problem appearing on an unpatched version?
How come it slipped through the tests?

This was referenced May 24, 2017
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@cblecker cblecker mentioned this issue May 24, 2017
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@dghubble dghubble mentioned this issue May 25, 2017
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@ixdy ixdy mentioned this issue Jun 13, 2017
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@jgehrcke jgehrcke mentioned this issue Jun 19, 2017
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@nielsole
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Backlinking for reference: https://events.ccc.de/congress/2017/Fahrplan/events/9021.html

@golang golang locked and limited conversation to collaborators Dec 28, 2018
@rsc rsc unassigned agl Jun 23, 2022
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