store URI: introduce multiple signatures support

src/libstore/binary-cache-store.cc

@@ -29,8 +29,17 @@ BinaryCacheStore::BinaryCacheStore(const Params & params)
     , Store(params)
 {
     if (secretKeyFile != "")
-        signer = std::make_unique<LocalSigner>(
-            SecretKey { readFile(secretKeyFile) });
+        signers.push_back(std::make_unique<LocalSigner>(
+            SecretKey { readFile(secretKeyFile) }));
+
+    if (secretKeyFiles != "") {
+        std::stringstream ss(secretKeyFiles);
+        Path keyPath;
+        while (std::getline(ss, keyPath, ',')) {
+            signers.push_back(std::make_unique<LocalSigner>(
+                SecretKey { readFile(keyPath) }));
+        }
+    }
 
     StringSink sink;
     sink << narVersionMagic1;
@@ -270,9 +279,9 @@ ref<const ValidPathInfo> BinaryCacheStore::addToStoreCommon(
     stats.narWriteCompressedBytes += fileSize;
     stats.narWriteCompressionTimeMs += duration;
 
-    /* Atomically write the NAR info file.*/
-    if (signer) narInfo->sign(*this, *signer);
+    narInfo->sign(*this, signers);
 
+    /* Atomically write the NAR info file.*/
     writeNarInfo(narInfo);
 
     stats.narInfoWrite++;

src/libstore/include/nix/store/binary-cache-store.hh

@@ -32,6 +32,9 @@ struct BinaryCacheStoreConfig : virtual StoreConfig
     const Setting<Path> secretKeyFile{this, "", "secret-key",
         "Path to the secret key used to sign the binary cache."};
 
+    const Setting<std::string> secretKeyFiles{this, "", "secret-keys",
+        "List of comma-separated paths to the secret keys used to sign the binary cache."};
+
     const Setting<Path> localNarCache{this, "", "local-nar-cache",
         "Path to a local cache of NARs fetched from this binary cache, used by commands such as `nix store cat`."};
 
@@ -57,7 +60,7 @@ class BinaryCacheStore : public virtual BinaryCacheStoreConfig,
 {
 
 private:
-    std::unique_ptr<Signer> signer;
+    std::vector<std::unique_ptr<Signer>> signers;
 
 protected:
 

src/libstore/include/nix/store/path-info.hh

@@ -144,6 +144,7 @@ struct ValidPathInfo : UnkeyedValidPathInfo {
     std::string fingerprint(const Store & store) const;
 
     void sign(const Store & store, const Signer & signer);
+    void sign(const Store & store, const std::vector<std::unique_ptr<Signer>> & signers);
 
     /**
      * @return The `ContentAddressWithReferences` that determines the

src/libstore/path-info.cc

@@ -40,6 +40,14 @@ void ValidPathInfo::sign(const Store & store, const Signer & signer)
     sigs.insert(signer.signDetached(fingerprint(store)));
 }
 
+void ValidPathInfo::sign(const Store & store, const std::vector<std::unique_ptr<Signer>> & signers)
+{
+    auto fingerprint = this->fingerprint(store);
+    for (auto & signer: signers) {
+        sigs.insert(signer->signDetached(fingerprint));
+    }
+}
+
 std::optional<ContentAddressWithReferences> ValidPathInfo::contentAddressWithReferences() const
 {
     if (! ca)

tests/functional/signing.sh

@@ -110,3 +110,13 @@ nix store verify --store "$TEST_ROOT"/store0 -r "$outPath2" --trusted-public-key
 
 # Content-addressed stuff can be copied without signatures.
 nix copy --to "$TEST_ROOT"/store0 "$outPathCA"
+
+# Test multiple signing keys
+nix copy --to "file://$TEST_ROOT/storemultisig?secret-keys=$TEST_ROOT/sk1,$TEST_ROOT/sk2" "$outPath"
+for file in "$TEST_ROOT/storemultisig/"*.narinfo; do
+    if [[ "$(grep -cE  '^Sig: cache[1,2]\.example.org' "$file")" -ne 2 ]]; then
+        echo "ERROR: Cannot find cache1.example.org and cache2.example.org signatures in ${file}"
+        cat "${file}"
+        exit 1
+    fi
+done