[Nix-dev] Authenticating binary substitutes

[Lluís Batlle i Rossell]

On Wed, May 22, 2013 at 05:12:20PM +0200, Ludovic Courtès wrote:
> Hello,
> 
> 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.
> 
> 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.
> 
> WDYT?  Could this be implemented in Hydra?

I add myself to the request.

The /nix-cache-info or /nix-signing-key files should be requested
only once and stored in the local system, unless the user deletes them. If they
are fetched at every run, we are doomed again.