in reply to cpan/cpanm integrity and authenticy checks concerns

You're right, but here's the problem: on the Internet, everyone is an Alice. It's not an Alice and Bob situation where they can engage in some trade-craft and exchange their public key fingerprints during a dinner date because they know each other.

If we drop the keyserver access requirement, what's to stop an evil mirror from creating a key pair in the name of the module developer and signing an evil module just for you?

  • Comment on Re: cpan/cpanm integrity and authenticy checks concerns

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Re^2: cpan/cpanm integrity and authenticy checks concerns
by hrcerq (Monk) on Jul 12, 2021 at 23:37 UTC

    Indeed, the keyserver has a very important role here (at least while OpenPGP is the chosen approach). I actually believe this part is all right as long as Internet access is avaiable.

    But my point is that security is not enforced in any way. Seems almost like it's an afterthought.

    And actually, I think there might be some workarounds (some with OpenPGP, some with other approaches):

    • With OpenPGP approach, maybe some keys from known developers could be shipped together with perl (or maybe in separate packages depending on the operating system). These keys take some time to expire, and could be used to check for new other keys, in a Web of Trust;
    • Outside of OpenPGP approach, however, there are options too. For instance, I like OpenBSD's approach, with signify . Every OpenBSD release contains the key necessary to verify the next release, so indirectly every new key is signed by its predecessor.

      Maybe this could be applied to every Perl distribution, in the sense that every distribution comes with the necessary key for the next version. That way, at least every update will be safe. It's worth noting these keys are relatively small (thanks to ED25519 algorithm), so shipping them is cheap.

      That way, only the first install would be unsafe, and a compromised key could be easily detected during updates.

    I know crypto solutions are not trivial, but I believe there are options. I completely agree with the idea of giving choice to the users, but I think security should be opt-out, not opt-in.

    return on_success() or die;

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      Thanks for the idea. Shipping a root key with Perl and signing (perhaps via a few intermediaries) the developers' keys with it to let them sign their distributions would solve part of the Alice problem by providing a way for the user to verify that the package has been signed with a key known to the owner of the key (CPAN) which was signed by the root (Perl) key. I agree that having this system is better than not having a way to validate a developer's key and that this should protect from the evil mirror problem if the existing Perl installation is clean (and that latter assumption we just have to trust, see "Reflections on trusting trust" by Ken Thompson).

      The current situation can be somewhat circumvented by only downloading packages from https://cpan.org/authors/id/... (effectively limiting oneself to a single mirror, which doesn't quite scale, and having to trust the HTTPS PKI, which is arguably not as good as a dedicated Perl PKI).

      It should also be noted that typical supply chain attacks on modules involve typosquatting and taking over unmaintained modules, which, aside the author's public key visibly changing, wouldn't raise any louder alerts: the attacker would look the same as any other CPAN citizen, but the signed code supplied by them would also be malicious. But that's a social problem, likely impossible to solve by purely technical means.

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        But then, how would you know that the "shipped root key" is authentic?
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