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

-Peff