On 20/02/15 10:22 AM, Florian Pelz wrote: > On 02/20/2015 03:59 PM, Daniel Micay wrote: >> The vast majority of users make use of the binary packages and the >> checksums do absolutely nothing to secure the main attack vector >> which is a compromise of the sources downloaded by the packager. It >> is only relevant to the tiny minority of people building a package >> with ABS. >> >> The more meaningful compromise needs to happen to the actual >> package in the repositories. A compromise of the server hosting the >> sources is the most likely way for this to happen. HTTPS can't do >> anything to defend against it. HTTPS can only defend against a MITM >> attack on a specific downstream packager. >> > > The difference is that if certain government organizations infiltrate > the Arch servers or upstream, they break everyone's security. They may > be less likely to do that compared to breaking just yours. Compromising the Arch servers doesn't provide the ability to produce valid signed packages, and compromising the upstream servers doesn't provide the ability to produce valid signed sources. You would need to compromise the machine used by the developer and gain access to their private key and whatever else you're after. There's little that can be done once that is accomplished... >> There is support for validating sources with GPG signatures, which >> is a complete solution to this issue. If you care, then file issues >> for any packages that aren't using the upstream signatures yet, and >> complain to upstream if they aren't signing the releases. >> > > This certainly is the right way to go, but I don't think enough > upstream projects care to make it a viable option for personal > computers today. PKGBUILD checksums provide less security, but they do > provide some. Lots of our packages already use them, and that's only a fraction of the ones that could be using them. Just look at how long the rebuild list for pacman 4.2's improved signing was or look at the Arch package source tree yourself. PKGBUILD checksums provide *zero*, yes *zero* security for the case that matters most, which is the build done by the packager. It does provide the ability for other people to verify that a MITM attack was not used to target a specific packager... but that is far, far less likely than a compromise of the sources on the upstream server and it can't do anything about that. Providing an audit trail is distinct from providing security, and there is more than one way to do that. Signed source tarballs would tackle the same thing while avoiding the problem of upstream clobbering the sources or the sources simply becoming unavailable. Many upstreams don't continue hosting sources for older versions... Clobbering the sources is common enough that a validation failure is only a bit suspicious and likely isn't even going to be investigated. That is the reality of the hashes - they are near useless. >> On 20/02/15 09:41 AM, Florian Pelz wrote: >>> I'm not sure if downloads over the git:// protocol are actually >>> verified, because the transfer is definitely not secure. I do >>> hope so. >> >> Git's read-only protocol is not authenticated. It supports SSH and >> HTTPS which do have two different forms of authentication, both of >> which are very flawed. Signed tags make a lot more sense, and you >> shouldn't be using code from development branches if you care a lot >> about robustness and security, since >> > > It is not authenticated, but I care about checksums. (Authentication > would be even better because it ensures others don't know what > software I am running -- but that is too much to ask.) I don't see why > SSH and HTTPS are flawed, other than a distrust in certificate > authorities. It can also only protect against a MITM attack against upstream and downstream, which as I already pointed out is not as likely as compromising the sources on the upstream server - and it can't do anything about that. Trust in certificate authorities is trust in many corporations and governments around the world. It's trust in tends of thousands of individuals with the ability to sign whatever they want. An attacker with the ability to perform a targeted MITM attack on a specific Arch developer likely has the ability to sign whatever they want. Compromising the upstream sources in a subtle way when they upload the next release will be nearly impossible to detect - only the upstream developer who uploaded the source tarball Git's SSH protocol implies having SSH access to at least a Git shell on the server and isn't ever used for read access in practice. SSH has a simple, sane whitelist-based model based on a public key / IP pair. It will warn whenever the server IP changes which is not at all uncommon and means that nearly every developer has learned to ignore it. > I still hope that git:// downloads use checksums. I'm not sure. They can do it if they're fetching a specific version...
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