Re: [PATCH 0/2] Re-integrate sha1dc
- Date: Thu, 16 Mar 2017 18:04:56 -0400
- From: Jeff King <peff@xxxxxxxx>
- Subject: Re: [PATCH 0/2] Re-integrate sha1dc
On Thu, Mar 16, 2017 at 01:24:02PM -0700, Linus Torvalds wrote:
> I suspect the first patch will not make it to the list since it's over
> 100kB in size, but oh well.. Junio and Jeff will see it.
Yep, it didn't make it, but I got it.
> It "WorksForMe(tm)" and the integration patches are now fairly trivial,
> since upstream already did the dieting and some of the semantic changes to
> gits more traditional C code.
There are a few things I think are worth changing. The die() message
should mention the sha1 we computed. That will be a big help if an old
version of git tries to unknowingly push a colliding object to a newer
version. The user will see "collision on sha1 1234.." which gives them a
starting point to figure out where they got the bad object from.
And to make that work, we have to disable the safe_hash feature (which
intentionally corrupts a colliding sha1). We _could_ rip it out
entirely, but since it only kicks in when we see a collision, I doubt
it's impacting anything.
I also updated the timings in my commit message, and added a basic test.
> I did leave the C++ wrapper lines that the sha1dc header files have grown
> in the meantime, I debated removing them but felt that "closer to
> upstream" was worth it.
Yeah, I independently made the same decision.
So here's my version. It's on top of the hash.h tweak, as well.
[1/5]: add collision-detecting sha1 implementation
[2/5]: sha1dc: adjust header includes for git
[3/5]: sha1dc: disable safe_hash feature
[4/5]: Makefile: add USE_SHA1DC knob
[5/5]: t0013: add a basic sha1 collision detection test
Makefile | 11 +
hash.h | 2 +
sha1dc/LICENSE.txt | 30 +
sha1dc/sha1.c | 1808 +++++++++++++++++++++++++++++++++++++++++++++++
sha1dc/sha1.h | 122 ++++
sha1dc/ubc_check.c | 363 ++++++++++
sha1dc/ubc_check.h | 44 ++
t/t0013-sha1dc.sh | 19 +
t/t0013/shattered-1.pdf | Bin 0 -> 422435 bytes
9 files changed, 2399 insertions(+)
create mode 100644 sha1dc/LICENSE.txt
create mode 100644 sha1dc/sha1.c
create mode 100644 sha1dc/sha1.h
create mode 100644 sha1dc/ubc_check.c
create mode 100644 sha1dc/ubc_check.h
create mode 100755 t/t0013-sha1dc.sh
create mode 100644 t/t0013/shattered-1.pdf