On Thu, 2020-01-23 at 02:25 +0100, Artur Juraszek wrote: > Hi all, > > While poking through Arch's package system, I noticed that despite its > bad reputation, MD5 remains a default, and even some kind of a > "recommendation", due > to its presence in the example PKBUILDs, hashing algorithm for file integrity > verification. > > Is there a reason to not have it changed to a more future-proof one? I mean, > at least for now, > it seems good enough to protect before a so-called "2nd preimage attack", > which is the primary > concern in the classic file verification scenario, BUT: > > a) given the huge size of AUR and its rather chaotic nature, it is not that > hard to imagine > _a_ malicious upstream which could try to sneak some nasty changes in its own > files, > with AUR maintainer not noticing anything - leveraging flaws which do exist > and are quite > well-explored even today. > > b) it's already shown its weaknesses and it is not going to be any better - > the only research direction > is to found more (practical) attacks against MD5, so faster the change, fewer > the people possibly > affected in the future > > Attaching a patch which, I think, replaces MD5 with SHA256 as a default > completely - it's my first > change in ABS-related code, though, so please do not hesitate to criticize if > something's wrong ;] > > -- > Artur Juraszek
I think we should change it to sha512 instead. sha256 and sha512 are pretty similar but sha512 is faster on 64-bit machine. Since 64-bit is the new standard for high-power computing, and the only architecture we support, it would be more beneficial to chose sha512. A quick benchmark on my machine confirms this: $ dd if=/dev/zero of=example.img bs=4096 count=512000 512000+0 records in 512000+0 records out 2097152000 bytes (2.1 GB, 2.0 GiB) copied, 2.77283 s, 756 MB/s $ time sha256sum example.img 274fbb979251bcaceab594dd89d5adfec310e8851e320b5b5f90fd5f18d76149 examp le.img real 4.79 user 4.47 sys 0.30 $ time sha512sum example.img 241497cb61e24fcdaf33a13f5635951ff7c21cb27904e6f3de7b221031b0216800cbce1 a667a66aafbdb7ffbfe2a39564b4cb48efea1d3721093fa7663e7a8c9 example.img real 3.33 user 3.09 sys 0.21 sha512 is ~1.5s than sha256 when calculating the checksum of a 2GiB zero-ed file. Thank you, Filipe Laíns
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