Re:SHA-1 'fully and practically broken' by new collision (2020)
by danachow on Tuesday October 12, 2021 @06:11PM
(#28845682)
No - after all, the most common use of digital signatures is to sign documents that can be easily tampered. All the security is in the signature, not the content being signed.
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Re:SHA-1 'fully and practically broken' by new collision (2020)
by lvh on Tuesday October 12, 2021 @06:20PM
(#28845775)
This makes no sense. Sure: you can generate an X.509 certificate that says whatever you want, but the point is that you can validate the signature and see that it's a forgery. In the case of a hash-addressed system like git, the problem is that the signature is over a collision, so it no longer certifies the thing its supposed to certify. Git uses the hash as a shorthand for a revision, including its entire history--so yes, it is using the hash that way.
By that logic, would MD5 be fine? MD4? CRC32?
Re:SHA-1 'fully and practically broken' by new collision (2020)
by wongarsu on Tuesday October 12, 2021 @06:24PM
(#28845820)
A digital signature usually signs (~encrypts) a hash of the content. So asking what exactly signing a commit or tag entails is a very valid question. I would expect that signing a tag is only as strong as SHA-1, since a tag is essentially a label for a commit hash. For signing commits I have no clue, but would be quite interested as well.