Sign Sparkle appcasts in Python

Scripts/sparkle/sign-appcast-kms.py

@@ -3,7 +3,7 @@
 
 Google Cloud KMS Ed25519 signing can only sign small payloads directly. Sparkle
 requires a standard EdDSA signature over the full update archive, so normal
-release artifacts use Sparkle's signing tool with the decrypted release key.
+release artifacts sign directly from the decrypted release seed.
 """
 
 from __future__ import annotations
@@ -58,32 +58,39 @@ def kms_sign(args: argparse.Namespace, payload: Path) -> str:
         return base64.b64encode(signature_path.read_bytes()).decode("ascii")
 
 
-def sign_update(args: argparse.Namespace, payload: Path) -> str:
+def read_sparkle_seed(key_path: Path) -> bytes:
+    key_data = key_path.read_bytes().strip()
+    if len(key_data) == 32:
+        return key_data
+    try:
+        decoded = base64.b64decode(key_data, validate=True)
+    except ValueError as exc:
+        raise ValueError(f"Sparkle key is not raw or base64 Ed25519 seed data: {key_path}") from exc
+    if len(decoded) != 32:
+        raise ValueError(f"Sparkle key must decode to a 32-byte Ed25519 seed: {key_path}")
+    return decoded
+
+
+def sign_with_release_seed(args: argparse.Namespace, payload: Path) -> str:
     key_path = Path(args.ed_key_path) if args.ed_key_path else None
     if key_path is None or not key_path.is_file():
         raise FileNotFoundError(
             "Sparkle artifact is too large for direct Google KMS Ed25519 signing "
             "and SPARKLE_EDDSA_KEY_PATH does not point to a key file"
         )
-    result = run([
+    from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey
-        args.sign_update,
+
-        "--ed-key-file",
+    seed = read_sparkle_seed(key_path)
-        str(key_path),
+    signature = Ed25519PrivateKey.from_private_bytes(seed).sign(payload.read_bytes())
-        "-p",
+    return base64.b64encode(signature).decode("ascii")
-        str(payload),
-    ])
-    signature = result.stdout.strip().splitlines()[-1].strip()
-    if not signature:
-        raise ValueError(f"Sparkle sign_update produced no signature for {payload}")
-    return signature
 
 
 def sparkle_signature(args: argparse.Namespace, payload: Path) -> str:
     if args.ed_key_path:
-        return sign_update(args, payload)
+        return sign_with_release_seed(args, payload)
     if payload.stat().st_size <= args.kms_max_input_bytes:
         return kms_sign(args, payload)
-    return sign_update(args, payload)
+    return sign_with_release_seed(args, payload)
 
 
 def enclosure_path(enclosure: ET.Element, artifact_dir: Path) -> Path:
@@ -130,7 +137,6 @@ def parse_args(argv: list[str]) -> argparse.Namespace:
     parser.add_argument("--kms-max-input-bytes", type=int, default=DEFAULT_KMS_MAX_INPUT_BYTES)
     parser.add_argument("--gcloud", default=os.environ.get("GCLOUD", "gcloud"))
     parser.add_argument("--ed-key-path", default=os.environ.get("SPARKLE_EDDSA_KEY_PATH"))
-    parser.add_argument("--sign-update", default=os.environ.get("SPARKLE_SIGN_UPDATE", "sign_update"))
     return parser.parse_args(argv)
 
 

docs/DISTRIBUTION.md

@@ -33,8 +33,8 @@ a different distribution certificate.
 Sparkle appcast signing keeps the `sparkle-ed25519` Google KMS key available
 for payloads small enough for direct KMS Ed25519 signing, but normal macOS
 release archives are larger than Google KMS accepts for direct Ed25519
-messages. Those archives are signed with Sparkle's `sign_update` using the
+messages. Those archives are signed directly from the decrypted release
-decrypted release `SPARKLE_EDDSA_KEY_PATH` so Sparkle receives the standard
+`SPARKLE_EDDSA_KEY_PATH` seed so Sparkle receives the standard
 full-archive EdDSA signature it verifies at update time. macOS release builds
 embed public EdDSA key
 `uugZuJeqvvKd91NZ6F1Fv2cQenUbIG/ZW3L9MuaEz30=` and point Sparkle metadata at

evolution/proposals/BEP-0009-release-infrastructure-and-store-upload-pipeline.md

@@ -145,10 +145,10 @@ The same change also makes the forge itself the release authority: release tags
   and future signing-service work. It uses `EC_SIGN_ED25519` with software
   protection level because Google KMS rejects Ed25519 for HSM protection. Google
   KMS also rejects normal macOS release archives as direct Ed25519 messages, so
-  the tester pipeline signs full-size Sparkle archives with Sparkle's
+  the tester pipeline signs full-size Sparkle archives directly from the
-  `sign_update` and the decrypted `SPARKLE_EDDSA_KEY_PATH` release secret until
+  decrypted `SPARKLE_EDDSA_KEY_PATH` release seed until a compatible KMS-backed
-  a compatible KMS-backed Sparkle signing service is introduced. macOS builds
+  Sparkle signing service is introduced. macOS builds embed public EdDSA key
-  embed public EdDSA key `uugZuJeqvvKd91NZ6F1Fv2cQenUbIG/ZW3L9MuaEz30=`.
+  `uugZuJeqvvKd91NZ6F1Fv2cQenUbIG/ZW3L9MuaEz30=`.
 - Use Namespace labels for platform lanes:
   - `namespace-profile-linux-medium`
   - `namespace-profile-macos-large`

flake.nix

@@ -61,6 +61,9 @@
             pkgs.nodejs
           else
             pkgs.nodejs_20;
+        python3WithCrypto = pkgs.python3.withPackages (pythonPackages: [
+          pythonPackages.cryptography
+        ]);
         optionalPackage = name: lib.optional (lib.hasAttr name pkgs) (lib.getAttr name pkgs);
         googleKmsPkcs11Package =
           if pkgs.stdenv.hostPlatform.isx86_64 && pkgs.stdenv.isLinux then
@@ -137,7 +140,7 @@ EOF
           curl
           jq
           nodejsPkg
-          python3
+          python3WithCrypto
           openssl
           rsync
           zip

infra/identity/README.md

@@ -85,9 +85,9 @@ Sparkle appcasts keep `sparkle-ed25519`, a Google KMS key with algorithm
 `EC_SIGN_ED25519` and software protection level, for small signing probes and
 future signing-service work. Google KMS rejects Ed25519 at HSM protection level
 and also rejects full-size macOS release archives as direct Ed25519 messages.
-The tester pipeline therefore signs normal Sparkle archives with Sparkle's
+The tester pipeline therefore signs normal Sparkle archives directly from the
-`sign_update` and the decrypted `SPARKLE_EDDSA_KEY_PATH` release secret so the
+decrypted `SPARKLE_EDDSA_KEY_PATH` release seed so the appcast contains the
-appcast contains the standard full-archive EdDSA signature Sparkle verifies.
+standard full-archive EdDSA signature Sparkle verifies.
 
 The public EdDSA key embedded in macOS release builds is: