This change is to simplify [Trustix](https://github.com/tweag/trustix) indexing and makes it possible to reconstruct this URL regardless of the compression used.
In particular this means that 7c2e9ca597/contrib/nix/nar/nar.go (L61-L71) can be removed and only the bits that are required to establish trust needs to be published in the Trustix build logs.
The name had become a misnomer since it's not only for substitution
from binary caches, but when adding/copying any
(non-content-addressed) path to a store.
Sodium's Ed25519 signatures are much shorter than OpenSSL's RSA
signatures. Public keys are also much shorter, so they're now
specified directly in the nix.conf option ‘binary-cache-public-keys’.
The new command ‘nix-store --generate-binary-cache-key’ generates and
prints a public and secret key.
NAR info files in binary caches can now have a cryptographic signature
that Nix will verify before using the corresponding NAR file.
To create a private/public key pair for signing and verifying a binary
cache, do:
$ openssl genrsa -out ./cache-key.sec 2048
$ openssl rsa -in ./cache-key.sec -pubout > ./cache-key.pub
You should also come up with a symbolic name for the key, such as
"cache.example.org-1". This will be used by clients to look up the
public key. (It's a good idea to number keys, in case you ever need
to revoke/replace one.)
To create a binary cache signed with the private key:
$ nix-push --dest /path/to/binary-cache --key ./cache-key.sec --key-name cache.example.org-1
The public key (cache-key.pub) should be distributed to the clients.
They should have a nix.conf should contain something like:
signed-binary-caches = *
binary-cache-public-key-cache.example.org-1 = /path/to/cache-key.pub
If all works well, then if Nix fetches something from the signed
binary cache, you will see a message like:
*** Downloading ‘http://cache.example.org/nar/7dppcj5sc1nda7l54rjc0g5l1hamj09j-subversion-1.7.11’ (signed by ‘cache.example.org-1’) to ‘/nix/store/7dppcj5sc1nda7l54rjc0g5l1hamj09j-subversion-1.7.11’...
On the other hand, if the signature is wrong, you get a message like
NAR info file `http://cache.example.org/7dppcj5sc1nda7l54rjc0g5l1hamj09j.narinfo' has an invalid signature; ignoring
Signatures are implemented as a single line appended to the NAR info
file, which looks like this:
Signature: 1;cache.example.org-1;HQ9Xzyanq9iV...muQ==
Thus the signature has 3 fields: a version (currently "1"), the ID of
key, and the base64-encoded signature of the SHA-256 hash of the
contents of the NAR info file up to but not including the Signature
line.
Issue #75.
adisbladis
Robert Hensing