Support cryptographically signed binary caches

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.

1 files changed, 17 insertions, 1 deletions

diff --git a/scripts/nix-push.in b/scripts/nix-push.in
index 2c392c415..bdd128a6f 100755
--- a/scripts/nix-push.in
+++ b/scripts/nix-push.in
@@ -10,6 +10,7 @@ use Nix::Config;
 use Nix::Store;
 use Nix::Manifest;
 use Nix::Utils;
+use Nix::Crypto;
 
 my $tmpDir = tempdir("nix-push.XXXXXX", CLEANUP => 1, TMPDIR => 1)
     or die "cannot create a temporary directory";
@@ -25,6 +26,8 @@ my $writeManifest = 0;
 my $manifestPath;
 my $archivesURL;
 my $link = 0;
+my $privateKeyFile;
+my $keyName;
 my @roots;
 
 for (my $n = 0; $n < scalar @ARGV; $n++) {
@@ -57,6 +60,14 @@ for (my $n = 0; $n < scalar @ARGV; $n++) {
         $archivesURL = $ARGV[$n];
     } elsif ($arg eq "--link") {
         $link = 1;
+    } elsif ($arg eq "--key") {
+        $n++;
+        die "$0: `$arg' requires an argument\n" unless $n < scalar @ARGV;
+        $privateKeyFile = $ARGV[$n];
+    } elsif ($arg eq "--key-name") {
+        $n++;
+        die "$0: `$arg' requires an argument\n" unless $n < scalar @ARGV;
+        $keyName = $ARGV[$n];
     } elsif (substr($arg, 0, 1) eq "-") {
         die "$0: unknown flag `$arg'\n";
     } else {
@@ -99,7 +110,7 @@ foreach my $storePath (@storePaths) {
     my $pathHash = substr(basename($storePath), 0, 32);
     my $narInfoFile = "$destDir/$pathHash.narinfo";
     if (-e $narInfoFile) {
-        my $narInfo = parseNARInfo($storePath, readFile($narInfoFile));
+        my $narInfo = parseNARInfo($storePath, readFile($narInfoFile), 0, $narInfoFile) or die "cannot read `$narInfoFile'\n";
         my $narFile = "$destDir/$narInfo->{url}";
         if (-e $narFile) {
             print STDERR "skipping existing $storePath\n";
@@ -245,6 +256,11 @@ for (my $n = 0; $n < scalar @storePaths2; $n++) {
         }
     }
 
+    if (defined $privateKeyFile && defined $keyName) {
+        my $sig = signString($privateKeyFile, $info);
+        $info .= "Signature: 1;$keyName;$sig\n";
+    }
+
     my $pathHash = substr(basename($storePath), 0, 32);
 
     $dst = "$destDir/$pathHash.narinfo";