diff --git a/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Abstractions/IMasterKeyProvider.cs b/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Abstractions/IMasterKeyProvider.cs
new file mode 100644
index 0000000..dd2eb5c
--- /dev/null
+++ b/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Abstractions/IMasterKeyProvider.cs
@@ -0,0 +1,24 @@
+namespace ZB.MOM.WW.Secrets.Abstractions;
+
+/// <summary>
+/// Supplies the AES-256 master key (KEK) used to wrap and unwrap per-secret data-encryption
+/// keys. Implementations resolve the key material from a configured source (environment,
+/// file, external KMS) and expose a stable, non-secret identifier for the active key so
+/// rotation can be recorded per row and reasoned about later.
+/// </summary>
+public interface IMasterKeyProvider
+{
+    /// <summary>
+    /// Returns the 32-byte AES-256 master key material.
+    /// </summary>
+    /// <returns>The 32-byte master key.</returns>
+    /// <exception cref="MasterKeyUnavailableException">The master key cannot be resolved.</exception>
+    ReadOnlyMemory<byte> GetMasterKey();
+
+    /// <summary>
+    /// The stable, non-secret identifier of the active key-encryption key (KEK). This value
+    /// is recorded on each stored row so that key rotation is legible and rows can be matched
+    /// to the KEK that wrapped their DEK.
+    /// </summary>
+    string KekId { get; }
+}
diff --git a/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Abstractions/ISecretCipher.cs b/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Abstractions/ISecretCipher.cs
new file mode 100644
index 0000000..6fe9876
--- /dev/null
+++ b/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Abstractions/ISecretCipher.cs
@@ -0,0 +1,35 @@
+namespace ZB.MOM.WW.Secrets.Abstractions;
+
+/// <summary>
+/// Envelope-encrypts and decrypts secret material. Each secret is sealed under a per-secret
+/// data-encryption key (DEK) that is itself wrapped by the master key (KEK) from an
+/// <see cref="IMasterKeyProvider"/>. The secret name is bound as additional authenticated
+/// data (AAD) so ciphertext cannot be silently relocated to a different name.
+/// </summary>
+public interface ISecretCipher
+{
+    /// <summary>
+    /// Envelope-encrypts <paramref name="plaintext"/>, binding it to <paramref name="name"/>
+    /// as additional authenticated data.
+    /// </summary>
+    /// <param name="name">The secret name, bound as AAD.</param>
+    /// <param name="plaintext">The secret plaintext to seal.</param>
+    /// <param name="contentType">How the plaintext should be interpreted by consumers.</param>
+    /// <returns>
+    /// A <see cref="StoredSecret"/> carrying the ciphertext, nonce, tag, and wrapped DEK, with
+    /// <see cref="StoredSecret.Revision"/> 0 and default timestamps — the store stamps the
+    /// revision and timestamps on persist.
+    /// </returns>
+    StoredSecret Encrypt(SecretName name, string plaintext, SecretContentType contentType);
+
+    /// <summary>
+    /// Decrypts the value carried by a stored row, verifying its authentication tag and the
+    /// name it was bound to.
+    /// </summary>
+    /// <param name="secret">The stored row to decrypt.</param>
+    /// <returns>The decrypted plaintext.</returns>
+    /// <exception cref="SecretDecryptionException">
+    /// The authentication tag fails to verify, or the row references an unknown or unavailable KEK.
+    /// </exception>
+    string Decrypt(StoredSecret secret);
+}
diff --git a/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Abstractions/ISecretReplicator.cs b/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Abstractions/ISecretReplicator.cs
new file mode 100644
index 0000000..a11dce8
--- /dev/null
+++ b/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Abstractions/ISecretReplicator.cs
@@ -0,0 +1,17 @@
+namespace ZB.MOM.WW.Secrets.Abstractions;
+
+/// <summary>
+/// Publishes an encrypted row to cluster peers. Core registers a no-op implementation;
+/// <c>ZB.MOM.WW.Secrets.Akka</c> (deferred) provides the real cluster implementation.
+/// </summary>
+public interface ISecretReplicator
+{
+    /// <summary>
+    /// Broadcasts the already-encrypted <paramref name="row"/> to peer nodes. This is a no-op
+    /// in single-node deployments.
+    /// </summary>
+    /// <param name="row">The encrypted row to replicate.</param>
+    /// <param name="ct">A token to cancel the operation.</param>
+    /// <returns>A task that completes when the row has been published.</returns>
+    Task PublishAsync(StoredSecret row, CancellationToken ct);
+}
diff --git a/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Abstractions/ISecretResolver.cs b/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Abstractions/ISecretResolver.cs
new file mode 100644
index 0000000..2335f37
--- /dev/null
+++ b/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Abstractions/ISecretResolver.cs
@@ -0,0 +1,19 @@
+namespace ZB.MOM.WW.Secrets.Abstractions;
+
+/// <summary>
+/// The consumer-facing read seam: resolves the current plaintext of a secret by name. This is
+/// the surface application code depends on to fetch secrets at runtime; every resolution is
+/// audited (the access, never the value).
+/// </summary>
+public interface ISecretResolver
+{
+    /// <summary>
+    /// Resolves and decrypts the current plaintext for <paramref name="name"/>.
+    /// </summary>
+    /// <param name="name">The secret to resolve.</param>
+    /// <param name="ct">A token to cancel the operation.</param>
+    /// <returns>
+    /// The decrypted plaintext, or <c>null</c> if the secret is absent or tombstoned.
+    /// </returns>
+    Task<string?> GetAsync(SecretName name, CancellationToken ct);
+}
diff --git a/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Abstractions/ISecretStore.cs b/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Abstractions/ISecretStore.cs
new file mode 100644
index 0000000..2662f3a
--- /dev/null
+++ b/ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Abstractions/ISecretStore.cs
@@ -0,0 +1,66 @@
+namespace ZB.MOM.WW.Secrets.Abstractions;
+
+/// <summary>
+/// Persists encrypted secret rows and exposes the read, list, and replication operations the
+/// core services build on. The store only ever handles the encrypted <see cref="StoredSecret"/>
+/// representation and its safe <see cref="SecretMetadata"/> projection — it never sees plaintext.
+/// Deletes are soft (tombstones) so removals can propagate across a cluster.
+/// </summary>
+public interface ISecretStore
+{
+    /// <summary>
+    /// Returns the row for <paramref name="name"/>, including a tombstoned row, or <c>null</c>
+    /// if no row exists.
+    /// </summary>
+    /// <param name="name">The secret to fetch.</param>
+    /// <param name="ct">A token to cancel the operation.</param>
+    /// <returns>The stored row, or <c>null</c> if absent.</returns>
+    Task<StoredSecret?> GetAsync(SecretName name, CancellationToken ct);
+
+    /// <summary>
+    /// Inserts the row, or overwrites an existing row in place, bumping its revision and
+    /// updated timestamp.
+    /// </summary>
+    /// <param name="row">The encrypted row to persist.</param>
+    /// <param name="ct">A token to cancel the operation.</param>
+    /// <returns>A task that completes when the row is persisted.</returns>
+    Task UpsertAsync(StoredSecret row, CancellationToken ct);
+
+    /// <summary>
+    /// Soft-deletes (tombstones) the row for <paramref name="name"/> so the deletion can
+    /// propagate to peers.
+    /// </summary>
+    /// <param name="name">The secret to tombstone.</param>
+    /// <param name="actor">The principal to record as <c>updated_by</c>, if known.</param>
+    /// <param name="ct">A token to cancel the operation.</param>
+    /// <returns><c>true</c> if a row was tombstoned; <c>false</c> if the row was absent.</returns>
+    Task<bool> DeleteAsync(SecretName name, string? actor, CancellationToken ct);
+
+    /// <summary>
+    /// Lists the safe metadata projection for all secrets — never ciphertext.
+    /// </summary>
+    /// <param name="includeDeleted">
+    /// When <c>true</c>, tombstoned rows are included; otherwise they are omitted.
+    /// </param>
+    /// <param name="ct">A token to cancel the operation.</param>
+    /// <returns>The metadata for the matching secrets.</returns>
+    Task<IReadOnlyList<SecretMetadata>> ListAsync(bool includeDeleted, CancellationToken ct);
+
+    /// <summary>
+    /// Returns a compact manifest — name, revision, updated timestamp, and tombstone flag per
+    /// secret — used for cluster anti-entropy reconciliation without exchanging ciphertext.
+    /// </summary>
+    /// <param name="ct">A token to cancel the operation.</param>
+    /// <returns>The manifest entries for all secrets.</returns>
+    Task<IReadOnlyList<SecretManifestEntry>> GetManifestAsync(CancellationToken ct);
+
+    /// <summary>
+    /// Applies a row received from a peer using last-writer-wins on
+    /// (<see cref="StoredSecret.UpdatedUtc"/>, <see cref="StoredSecret.Revision"/>). A row that
+    /// is not newer than the local row is ignored.
+    /// </summary>
+    /// <param name="row">The replicated encrypted row to apply.</param>
+    /// <param name="ct">A token to cancel the operation.</param>
+    /// <returns>A task that completes when the row has been applied or ignored.</returns>
+    Task ApplyReplicatedAsync(StoredSecret row, CancellationToken ct);
+}