kernel/git - git - PowerEL Git System

Tree: 49d166081b

Author	SHA1	Message	Date
Jonathan Nieder	0ed8d8da37	doc hash-function-transition: pick SHA-256 as NewHash From a security perspective, it seems that SHA-256, BLAKE2, SHA3-256, K12, and so on are all believed to have similar security properties. All are good options from a security point of view. SHA-256 has a number of advantages: * It has been around for a while, is widely used, and is supported by just about every single crypto library (OpenSSL, mbedTLS, CryptoNG, SecureTransport, etc). * When you compare against SHA1DC, most vectorized SHA-256 implementations are indeed faster, even without acceleration. * If we're doing signatures with OpenPGP (or even, I suppose, CMS), we're going to be using SHA-2, so it doesn't make sense to have our security depend on two separate algorithms when either one of them alone could break the security when we could just depend on one. So SHA-256 it is. Update the hash-function-transition design doc to say so. After this patch, there are no remaining instances of the string "NewHash", except for an unrelated use from 2008 as a variable name in t/t9700/test.pl. Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Acked-by: brian m. carlson <sandals@crustytoothpaste.net> Acked-by: Johannes Schindelin <Johannes.Schindelin@gmx.de> Acked-by: Dan Shumow <danshu@microsoft.com> Signed-off-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>	7 years ago
Ævar Arnfjörð Bjarmason	13f5e09821	doc hash-function-transition: note the lack of a changelog The changelog embedded in the document pre-dates the addition of the document to git.git (it used to be a Google Doc), so it only goes up to `752414ae43` ("technical doc: add a design doc for hash function transition", 2017-09-27). Since then I made some small edits to it, which would have been worthy of including in this changelog (but weren't). Instead of amending it to include these, just note that future changes will be noted in the log. Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>	7 years ago
Ævar Arnfjörð Bjarmason	5988eb631a	doc hash-function-transition: clarify what SHAttered means Attempt to clarify what the SHAttered attack means in practice for Git. The previous version of the text made no mention whatsoever of Git already having a mitigation for this specific attack, which the SHAttered researchers claim will detect cryptanalytic collision attacks. I may have gotten some of the nuances wrong, but as far as I know this new text accurately summarizes the current situation with SHA-1 in git. I.e. git doesn't really use SHA-1 anymore, it uses Hardened-SHA-1 (they just so happen to produce the same outputs 99.99999999999...% of the time). Thus the previous text was incorrect in asserting that: [...]As a result [of SHAttered], SHA-1 cannot be considered cryptographically secure any more[...] That's not the case. We have a mitigation against SHAttered, however we consider it prudent to move to work towards a NewHash should future vulnerabilities in either SHA-1 or Hardened-SHA-1 emerge. Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>	7 years ago
Ævar Arnfjörð Bjarmason	45fa195ff0	doc hash-function-transition: clarify how older gits die on NewHash Change the "Repository format extension" to accurately describe what happens with different versions of Git when they encounter NewHash repositories, instead of only saying what happens with versions v2.7.0 and later. See `ab9cb76f66` ("Repository format version check.", 2005-11-25) and `00a09d57eb` ("introduce "extensions" form of core.repositoryformatversion", 2015-06-23) for the relevant changes to the setup code where these variables are checked. Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>	7 years ago
Jonathan Nieder	752414ae43	technical doc: add a design doc for hash function transition This document describes what a transition to a new hash function for Git would look like. Add it to Documentation/technical/ as the plan of record so that future changes can be recorded as patches. Also-by: Brandon Williams <bmwill@google.com> Also-by: Jonathan Tan <jonathantanmy@google.com> Also-by: Stefan Beller <sbeller@google.com> Signed-off-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>	7 years ago