Re: Authenticating binary substitutes

[Ludovic Courtès]

(Re-adding address@hidden)

Eelco Dolstra <address@hidden> skribis:

> On 22/05/13 11:12, Ludovic Courtès wrote:
>
>> Currently the “binary cache” substituter relies on DNS to authenticate
>> downloaded binaries: anything coming from, say, hydra.nixos.org is
>> considered authentic, because hydra.nixos.org is listed in the
>> ‘trusted-binary-cache’ list.
>> 
>> This is obviously subject to person-in-the-middle attacks: one could
>> connect over Wifi to somebody else’s network, which happens to redirect
>> hydra.nixos.org to evil.example.com, and end up downloading evil binaries.
>
> There is an issue about this:
>
> https://github.com/NixOS/nix/issues/75

Ah, good.

>> I was thinking of a simple extension to solve that:
>> 
>>   1a. The /nix-cache-info file would contain an (optional)
>>      ‘OpenPGPFingerprint’ field, to announce the fingerprint of the
>>      OpenPGP key used to sign Nars.
>> 
>>   1b. In addition to, or alternatively, a /nix-signing-key file would be
>>       served, containing the OpenPGP key used to sign Nars.
>> 
>>   2.  In addition to serving, say,
>>       /nar/zwpx7d0sv36fi4xpwqx2dak0axx5nji8-gmp-5.1.1, the server would
>>       also serve /nar/zwpx7d0sv36fi4xpwqx2dak0axx5nji8-gmp-5.1.1.sig, an
>>       OpenPGP binary signature of the uncompressed Nar.
>
> How about: rather than relying on nix-cache-info, nix.conf should specify a 
> list
> of fingerprints of trusted OpenPGP signing keys.

Yes (I was focusing on the protocol, to start with.)

> Then when we fetch a .narinfo, we check whether it is signed by a
> trusted key.  This way you don't have the problem Lluís described.

I think it’s enough to sign nars.  What do you think it would add to
sign narinfos as well?

Thanks,
Ludo’.