Re: [PATCH v2 10/13] Add a base implementation of SHA-256 support
- From
brian m. carlson <sandals@crustytoothpaste.net>
- Date
- Oct 15, 2018, 23:30 UTC
- Message-ID
- <20181015233035.GB432229@genre.crustytoothpaste.net>
- In-Reply-To
- <CACsJy8AOu-SdLu+MQKOzVLEy0SM0r45TjwZYkD_S5W756hWRpw@mail.gmail.com>
On Mon, Oct 15, 2018 at 04:59:12PM +0200, Duy Nguyen wrote:
Show 24 quoted lines
> On Mon, Oct 15, 2018 at 4:23 AM brian m. carlson > <sandals@crustytoothpaste.net> wrote: > > > > SHA-1 is weak and we need to transition to a new hash function. For > > some time, we have referred to this new function as NewHash. Recently, > > we decided to pick SHA-256 as NewHash. > > > > Add a basic implementation of SHA-256 based off libtomcrypt, which is in > > the public domain. Optimize it and restructure it to meet our coding > > standards. Place it in a directory called "sha256" where it and any > > future implementations can live so as to avoid a proliferation of > > implementation directories. > > > > Wire up SHA-256 in the list of hash algorithms, and add a test that the > > algorithm works correctly. > > > > Note that with this patch, it is still not possible to switch to using > > SHA-256 in Git. Additional patches are needed to prepare the code to > > handle a larger hash algorithm and further test fixes are needed. > > At some point I assume SHA-256 will become functional and be part of a > git release without all file formats updated to support multiple > hashes. Should we somehow discourage the user from using it because it > will break when all file formats are finally updated?
In order to activate SHA-256 in the codebase, currently you need a patch to force it on. Otherwise, the code is simply inert and does nothing (other than in the test-tool). I've included the patch below so you can see what it does (or if you want to play around with it).
Without this patch, Git remains fully SHA-1 and can't access any of the SHA-256 code. I have some very preliminary patches that do wire up extensions.objectFormat (branch object-id-part15 [sic]) but I haven't picked them up in a while. (I need to finish test fixes first.)
Making the codebase run in SHA-256 mode with a Git that supports both algorithms but defaults to SHA-1 is currently seriously broken, even with the object-id-part15 branch. When those patches go in, they will be behind a developer flag to prevent wholesale chaos and segfaults.
So in summary, no, I don't think a developer flag is necessary at this point.
-- >% -- From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: "brian m. carlson" <sandals@crustytoothpaste.net> Date: Wed, 25 Jul 2018 23:48:30 +0000 Subject: [PATCH] Switch default hash algorithm to SHA-256 for testing
Set the default hash algorithm to SHA-256 for testing purposes.
This is a test commit and should not be used in production.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net> --- repository.c | 2 +- setup.c | 2 +- t/test-lib-functions.sh | 4 +--- t/test-lib.sh | 13 ++++++++----- 4 files changed, 11 insertions(+), 10 deletions(-)
diff --git a/repository.c b/repository.c index 5dd1486718..4ce50ea670 100644 --- a/repository.c +++ b/repository.c @@ -17,7 +17,7 @@ void initialize_the_repository(void) the_repo.objects = raw_object_store_new(); the_repo.parsed_objects = parsed_object_pool_new(); - repo_set_hash_algo(&the_repo, GIT_HASH_SHA1); + repo_set_hash_algo(&the_repo, GIT_HASH_SHA256); } static void expand_base_dir(char **out, const char *in, diff --git a/setup.c b/setup.c index b24c811c1c..2b4cc4e5a4 100644 --- a/setup.c +++ b/setup.c @@ -490,7 +490,7 @@ int read_repository_format(struct repository_format *format, const char *path) memset(format, 0, sizeof(*format)); format->version = -1; format->is_bare = -1; - format->hash_algo = GIT_HASH_SHA1; + format->hash_algo = GIT_HASH_SHA256; string_list_init(&format->unknown_extensions, 1); git_config_from_file(check_repo_format, path, format); return format->version; diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh index dfa1bebb46..91cf2b9d40 100644 --- a/t/test-lib-functions.sh +++ b/t/test-lib-functions.sh @@ -1165,9 +1165,7 @@ test_set_hash () { # Detect the hash algorithm in use. test_detect_hash () { - # Currently we only support SHA-1, but in the future this function will - # actually detect the algorithm in use. - test_hash_algo='sha1' + test_hash_algo='sha256' } # Load common hash metadata and common placeholder object IDs for use with diff --git a/t/test-lib.sh b/t/test-lib.sh index 3f95bfda60..bb507f2d4f 100644 --- a/t/test-lib.sh +++ b/t/test-lib.sh @@ -176,18 +176,21 @@ esac # Convenience # -# A regexp to match 5, 35 and 40 hexdigits +# A regexp to match 4, 5, 35, 40, and 64 hexdigits +_x04='[0-9a-f][0-9a-f][0-9a-f][0-9a-f]' _x05='[0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f]' _x35="$_x05$_x05$_x05$_x05$_x05$_x05$_x05" _x40="$_x35$_x05" +_x64="$_x40$_x05$_x05$_x05$_x05$_x04" # Zero SHA-1 _z40=0000000000000000000000000000000000000000 +_z64=0000000000000000000000000000000000000000000000000000000000000000 -OID_REGEX="$_x40" -ZERO_OID=$_z40 -EMPTY_TREE=4b825dc642cb6eb9a060e54bf8d69288fbee4904 -EMPTY_BLOB=e69de29bb2d1d6434b8b29ae775ad8c2e48c5391 +OID_REGEX="$_x64" +ZERO_OID=$_z64 +EMPTY_TREE=6ef19b41225c5369f1c104d45d8d85efa9b057b53b14b4b9b939dd74decc5321 +EMPTY_BLOB=473a0f4c3be8a93681a267e3b1e9a7dcda1185436fe141f7749120a303721813 # Line feed LF=' -- >% --
-- brian m. carlson: Houston, Texas, US OpenPGP: https://keybase.io/bk2204