diff --git a/ZB.MOM.WW.Secrets/Directory.Packages.props b/ZB.MOM.WW.Secrets/Directory.Packages.props
index dab26a3..0a39b60 100644
--- a/ZB.MOM.WW.Secrets/Directory.Packages.props
+++ b/ZB.MOM.WW.Secrets/Directory.Packages.props
@@ -30,6 +30,17 @@
     <PackageVersion Include="Akka.Remote" Version="1.5.62" />
     <PackageVersion Include="Akka.TestKit.Xunit2" Version="1.5.62" />
 
+    <!-- gRPC secrets hub (ZB.MOM.WW.Secrets.Replicator.Grpc).
+         2.76.0 / 3.34.1 is the version the whole family already resolves — ScadaBridge and
+         OtOpcUa pin exactly these, and the sibling ZB.MOM.WW.LocalDb libraries floor them there.
+         A consumer taking the hub alongside LocalDb replication must not be pushed into a
+         downgrade warning or an unplanned Grpc bump just to adopt secret replication. -->
+    <PackageVersion Include="Google.Protobuf" Version="3.34.1" />
+    <PackageVersion Include="Grpc.AspNetCore" Version="2.76.0" />
+    <PackageVersion Include="Grpc.Core.Api" Version="2.76.0" />
+    <PackageVersion Include="Grpc.Net.Client" Version="2.76.0" />
+    <PackageVersion Include="Grpc.Tools" Version="2.76.0" />
+
     <!-- Cryptography -->
     <!-- 9.0.4, not 9.0.0: Microsoft.Data.SqlClient 6.0.2 pulls System.Configuration.ConfigurationManager
          9.0.4, which requires ProtectedData >= 9.0.4. With transitive pinning on, the lower central
diff --git a/ZB.MOM.WW.Secrets/ZB.MOM.WW.Secrets.slnx b/ZB.MOM.WW.Secrets/ZB.MOM.WW.Secrets.slnx
index 5f821d9..891a006 100644
--- a/ZB.MOM.WW.Secrets/ZB.MOM.WW.Secrets.slnx
+++ b/ZB.MOM.WW.Secrets/ZB.MOM.WW.Secrets.slnx
@@ -4,6 +4,7 @@
     <Project Path="src/ZB.MOM.WW.Secrets/ZB.MOM.WW.Secrets.csproj" />
     <Project Path="src/ZB.MOM.WW.Secrets.Replicator.SqlServer/ZB.MOM.WW.Secrets.Replicator.SqlServer.csproj" />
     <Project Path="src/ZB.MOM.WW.Secrets.Replicator.AkkaDotNet/ZB.MOM.WW.Secrets.Replicator.AkkaDotNet.csproj" />
+    <Project Path="src/ZB.MOM.WW.Secrets.Replicator.Grpc/ZB.MOM.WW.Secrets.Replicator.Grpc.csproj" />
     <Project Path="src/ZB.MOM.WW.Secrets.Ui/ZB.MOM.WW.Secrets.Ui.csproj" />
     <Project Path="src/ZB.MOM.WW.Secrets.Cli/ZB.MOM.WW.Secrets.Cli.csproj" />
   </Folder>
diff --git a/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Replicator.Grpc/Protos/secrets_hub.proto b/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Replicator.Grpc/Protos/secrets_hub.proto
new file mode 100644
index 0000000..7d7f84b
--- /dev/null
+++ b/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Replicator.Grpc/Protos/secrets_hub.proto
@@ -0,0 +1,142 @@
+syntax = "proto3";
+
+package zb.mom.ww.secrets.hub.v1;
+
+option csharp_namespace = "ZB.MOM.WW.Secrets.Replicator.Grpc.V1";
+
+// The central-hosted secrets hub, as seen by a site node.
+//
+// PULL-ONLY BY CONSTRUCTION. This service mirrors exactly the read half of
+// ISecretReplicationHub — GetManifestAsync and GetManyAsync. Its third method,
+// ApplyReplicatedAsync, is deliberately NOT mirrored: in this topology every update
+// originates at central, and a site node is a strict follower. The narrow contract IS the
+// enforcement — with no write RPC on the wire, a mis-wired or compromised site node has no
+// way to push a row into the hub, regardless of what its authorization happens to allow.
+// Adding a third RPC to this service would silently retire that guarantee, so do not.
+//
+// Everything crossing this boundary is ciphertext or metadata about ciphertext. The
+// key-encryption key (KEK) never travels: SecretRow carries the KEK's *identifier* and the
+// DEK *wrapped* by it, and every node in a replicating deployment is configured with the
+// same KEK out of band.
+service SecretsHub {
+  // Returns the hub's full manifest — the compact per-secret state (name, revision,
+  // timestamp, tombstone flag) a follower needs to work out which rows it is missing or
+  // behind on, without transferring any ciphertext.
+  rpc GetManifest(GetManifestRequest) returns (GetManifestResponse);
+
+  // Fetches the named encrypted rows in bulk. Names absent from the hub are omitted from
+  // the response rather than reported as errors — the caller's manifest may be a moment
+  // stale, and a row deleted between the two calls is not a fault.
+  rpc GetSecrets(GetSecretsRequest) returns (GetSecretsResponse);
+}
+
+// Request for the hub's full manifest. Empty today; a message rather than
+// google.protobuf.Empty so filters (a name prefix, a revision floor) can be added later
+// without a breaking signature change.
+message GetManifestRequest {
+}
+
+message GetManifestResponse {
+  repeated ManifestEntry entries = 1;
+}
+
+message GetSecretsRequest {
+  // Normalized secret names to fetch. Each is re-validated as a SecretName on the far
+  // side; the wire type is a plain string because SecretName is a validated wrapper, not
+  // a distinct serialized shape.
+  repeated string names = 1;
+}
+
+message GetSecretsResponse {
+  repeated SecretRow secrets = 1;
+}
+
+// The wire form of ZB.MOM.WW.Secrets.Abstractions.SecretManifestEntry.
+message ManifestEntry {
+  // SecretManifestEntry.Name (SecretName.Value).
+  string name = 1;
+
+  // SecretManifestEntry.Revision.
+  int64 revision = 2;
+
+  // SecretManifestEntry.UpdatedUtc, as a round-trip ISO-8601 ("O") string.
+  string updated_utc = 3;
+
+  // SecretManifestEntry.IsDeleted.
+  bool is_deleted = 4;
+}
+
+// The wire form of ZB.MOM.WW.Secrets.Abstractions.StoredSecret — every field, nothing more.
+//
+// This is a hand-written mirror rather than a serialization of the domain type, for the
+// same reason the Akka replicator's SecretRowDto is: it makes the trust boundary
+// structural. The whole payload is visible as a flat set of primitives that a reader can
+// check against "ciphertext only, never the KEK" at a glance, and a field added to
+// StoredSecret in future cannot start crossing the network merely by existing.
+//
+// TIMESTAMPS are ISO-8601 round-trip ("O") strings, not google.protobuf.Timestamp. Two
+// reasons. (1) Losslessness: DateTimeOffset carries an offset and 100 ns ticks;
+// Timestamp is a UTC instant, so a non-UTC DateTimeOffset does not round-trip through it
+// unchanged. (2) Consistency: the Akka replicator's DTO already made this choice, and the
+// stores persist the same "O" form — one representation family-wide means a row relayed
+// hub -> site is byte-identical to the row central holds, which the live gates assert.
+//
+// NULLABLE .NET fields use proto3 explicit presence (`optional`) so that null and empty
+// string stay distinguishable end to end; a plain proto3 string would collapse both to "".
+message SecretRow {
+  // StoredSecret.Name (SecretName.Value).
+  string name = 1;
+
+  // StoredSecret.Description (nullable).
+  optional string description = 2;
+
+  // StoredSecret.ContentType, as the SecretContentType enum MEMBER NAME. A proto enum was
+  // rejected: proto3 decodes an unknown enum number to the zero value, which here would
+  // silently retype a secret as Text. A name is parsed strictly on the far side, so an
+  // unrecognized content type is rejected at the boundary instead of persisted.
+  string content_type = 3;
+
+  // StoredSecret.Ciphertext — AES-256-GCM ciphertext of the plaintext.
+  bytes ciphertext = 4;
+
+  // StoredSecret.Nonce — nonce sealing `ciphertext`.
+  bytes nonce = 5;
+
+  // StoredSecret.Tag — authentication tag for `ciphertext`.
+  bytes tag = 6;
+
+  // StoredSecret.WrappedDek — the per-secret data key, wrapped by the KEK. The KEK itself
+  // never travels.
+  bytes wrapped_dek = 7;
+
+  // StoredSecret.WrapNonce — nonce used to wrap `wrapped_dek`.
+  bytes wrap_nonce = 8;
+
+  // StoredSecret.WrapTag — authentication tag for `wrapped_dek`.
+  bytes wrap_tag = 9;
+
+  // StoredSecret.KekId — an identifier for the wrapping key, not key material.
+  string kek_id = 10;
+
+  // StoredSecret.Revision — monotonic; the last-writer-wins tie-break.
+  int64 revision = 11;
+
+  // StoredSecret.IsDeleted — tombstone flag.
+  bool is_deleted = 12;
+
+  // StoredSecret.DeletedUtc (nullable), as a round-trip ISO-8601 ("O") string.
+  optional string deleted_utc = 13;
+
+  // StoredSecret.CreatedUtc, as a round-trip ISO-8601 ("O") string.
+  string created_utc = 14;
+
+  // StoredSecret.UpdatedUtc, as a round-trip ISO-8601 ("O") string — the primary
+  // last-writer-wins ordering key, so its representation has to be exact.
+  string updated_utc = 15;
+
+  // StoredSecret.CreatedBy (nullable).
+  optional string created_by = 16;
+
+  // StoredSecret.UpdatedBy (nullable).
+  optional string updated_by = 17;
+}
diff --git a/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Replicator.Grpc/ZB.MOM.WW.Secrets.Replicator.Grpc.csproj b/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Replicator.Grpc/ZB.MOM.WW.Secrets.Replicator.Grpc.csproj
new file mode 100644
index 0000000..404e484
--- /dev/null
+++ b/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Replicator.Grpc/ZB.MOM.WW.Secrets.Replicator.Grpc.csproj
@@ -0,0 +1,57 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+    <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    <RootNamespace>ZB.MOM.WW.Secrets.Replicator.Grpc</RootNamespace>
+  </PropertyGroup>
+
+  <PropertyGroup>
+    <IsPackable>true</IsPackable>
+    <PackageId>ZB.MOM.WW.Secrets.Replicator.Grpc</PackageId>
+    <Authors>ZB.MOM.WW</Authors>
+    <Description>Central-hosted gRPC secrets hub (pull-only) for the ZB.MOM.WW SCADA family — site nodes follow central, ciphertext-only.</Description>
+    <PackageProjectUrl>https://gitea.dohertylan.com/dohertj2/zb-mom-ww-secrets</PackageProjectUrl>
+    <RepositoryUrl>https://gitea.dohertylan.com/dohertj2/zb-mom-ww-secrets</RepositoryUrl>
+  </PropertyGroup>
+
+  <!-- One package carries BOTH halves of the contract: the hub service base class hosted at
+       central and the follower client dialled from a site node. GrpcServices="Both" is what
+       makes that possible from a single .proto compile. -->
+  <ItemGroup>
+    <Protobuf Include="Protos/secrets_hub.proto" GrpcServices="Both" ProtoRoot="Protos" />
+  </ItemGroup>
+
+  <!-- Grpc.AspNetCore brings the server-side hosting surface (MapGrpcService), which needs the
+       ASP.NET Core shared framework. That framework reference also supplies the whole
+       Microsoft.Extensions.* surface the siblings reference explicitly (DI, Options,
+       Configuration, Hosting, Logging), so this project deliberately carries no PackageReference
+       for them — NuGet reports each as prunable (NU1510), which is an error here. -->
+  <ItemGroup>
+    <FrameworkReference Include="Microsoft.AspNetCore.App" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\ZB.MOM.WW.Secrets\ZB.MOM.WW.Secrets.csproj" />
+    <ProjectReference Include="..\ZB.MOM.WW.Secrets.Abstractions\ZB.MOM.WW.Secrets.Abstractions.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Google.Protobuf" />
+    <PackageReference Include="Grpc.AspNetCore" />
+    <PackageReference Include="Grpc.Net.Client" />
+    <PackageReference Include="Grpc.Core.Api" />
+    <PackageReference Include="Grpc.Tools">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+  </ItemGroup>
+
+  <ItemGroup>
+    <InternalsVisibleTo Include="ZB.MOM.WW.Secrets.Replicator.Grpc.Tests" />
+  </ItemGroup>
+
+</Project>