feat: bind each node to the binary it runs at its first handshake; refuse changes that are not in a CI-signed manifest [CI]

backend/src/MoShiro.Backend.Application/Updates/ReleaseSignature.cs

@@ -0,0 +1,25 @@
+using System.Security.Cryptography;
+using System.Text;
+
+namespace MoShiro.Backend.Application;
+
+/// <summary>
+/// 发布清单的签名校验：用 Backend 内嵌的 CI 发布公钥（<c>packaging/update/release-key.pub.pem</c>）验 ECDSA P-256 / SHA-256（DER）签名，签名对象是清单的原始字节。
+/// 登记清单因此不需要任何令牌：能被登记的只有 CI 签过的清单，节点的更新器之后还会用本机的公钥再验一遍。
+/// </summary>
+public static class ReleaseSignature
+{
+    public static bool Verify(string publicKeyPem, string manifest, string signatureBase64)
+    {
+        try
+        {
+            using var key = ECDsa.Create();
+            key.ImportFromPem(publicKeyPem);
+            return key.VerifyData(Encoding.UTF8.GetBytes(manifest), Convert.FromBase64String(signatureBase64), HashAlgorithmName.SHA256, DSASignatureFormat.Rfc3279DerSequence);
+        }
+        catch (Exception ex) when (ex is FormatException or CryptographicException or ArgumentException)
+        {
+            return false;
+        }
+    }
+}