[Nix-dev] Authenticating binary substitutes

[Eelco Dolstra]

Hi,

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

BTW, as a workaround, you can use https://nixos.org/binary-cache/.  But I'm not
sure if the binary cache substituter insists on a known SSL certificate...

> 
> 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.  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.

-- 
Eelco Dolstra | LogicBlox, Inc. | http://nixos.org/~eelco/