diff --git a/apub-privatekey/Cargo.toml b/apub-privatekey/Cargo.toml
new file mode 100644
index 0000000..5fa2d58
--- /dev/null
+++ b/apub-privatekey/Cargo.toml
@@ -0,0 +1,11 @@
+[package]
+name = "apub-privatekey"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+async-trait = "0.1.51"
+serde = { version = "1", features = ["derive"] }
+url = { version = "2", features = ["serde"] }
diff --git a/apub-privatekey/src/lib.rs b/apub-privatekey/src/lib.rs
new file mode 100644
index 0000000..a2c7007
--- /dev/null
+++ b/apub-privatekey/src/lib.rs
@@ -0,0 +1,184 @@
+use std::{
+    ops::{Deref, DerefMut},
+    rc::Rc,
+    str::FromStr,
+    sync::Arc,
+};
+use url::Url;
+
+#[async_trait::async_trait(?Send)]
+pub trait PrivateKeyRepo {
+    type Error;
+
+    async fn store(
+        &self,
+        actor_id: Url,
+        key_id: KeyId,
+        private_key_pem: String,
+    ) -> Result<(), Self::Error>;
+
+    async fn fetch(&self, actor_id: &Url) -> Result<(KeyId, String), Self::Error>;
+}
+
+pub trait PrivateKeyRepoFactory {
+    type PrivateKeyRepo: PrivateKeyRepo;
+
+    fn build_private_key_repo(&self) -> Self::PrivateKeyRepo;
+}
+
+#[derive(
+    Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash, serde::Deserialize, serde::Serialize,
+)]
+#[serde(transparent)]
+pub struct KeyId(Url);
+
+impl KeyId {
+    pub fn into_inner(this: Self) -> Url {
+        this.0
+    }
+}
+
+impl FromStr for KeyId {
+    type Err = <Url as FromStr>::Err;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        Ok(KeyId(Url::from_str(s)?))
+    }
+}
+
+impl Deref for KeyId {
+    type Target = Url;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl DerefMut for KeyId {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+impl AsRef<Url> for KeyId {
+    fn as_ref(&self) -> &Url {
+        &self.0
+    }
+}
+
+impl AsMut<Url> for KeyId {
+    fn as_mut(&mut self) -> &mut Url {
+        &mut self.0
+    }
+}
+
+impl From<Url> for KeyId {
+    fn from(url: Url) -> Self {
+        KeyId(url)
+    }
+}
+
+#[async_trait::async_trait(?Send)]
+impl<'a, T> PrivateKeyRepo for &'a T
+where
+    T: PrivateKeyRepo,
+{
+    type Error = T::Error;
+
+    async fn store(
+        &self,
+        actor_id: Url,
+        key_id: KeyId,
+        private_key_pem: String,
+    ) -> Result<(), Self::Error> {
+        T::store(self, actor_id, key_id, private_key_pem).await
+    }
+
+    async fn fetch(&self, actor_id: &Url) -> Result<(KeyId, String), Self::Error> {
+        T::fetch(self, actor_id).await
+    }
+}
+
+#[async_trait::async_trait(?Send)]
+impl<'a, T> PrivateKeyRepo for &'a mut T
+where
+    T: PrivateKeyRepo,
+{
+    type Error = T::Error;
+
+    async fn store(
+        &self,
+        actor_id: Url,
+        key_id: KeyId,
+        private_key_pem: String,
+    ) -> Result<(), Self::Error> {
+        T::store(self, actor_id, key_id, private_key_pem).await
+    }
+
+    async fn fetch(&self, actor_id: &Url) -> Result<(KeyId, String), Self::Error> {
+        T::fetch(self, actor_id).await
+    }
+}
+
+#[async_trait::async_trait(?Send)]
+impl<T> PrivateKeyRepo for Box<T>
+where
+    T: PrivateKeyRepo,
+{
+    type Error = T::Error;
+
+    async fn store(
+        &self,
+        actor_id: Url,
+        key_id: KeyId,
+        private_key_pem: String,
+    ) -> Result<(), Self::Error> {
+        T::store(self, actor_id, key_id, private_key_pem).await
+    }
+
+    async fn fetch(&self, actor_id: &Url) -> Result<(KeyId, String), Self::Error> {
+        T::fetch(self, actor_id).await
+    }
+}
+
+#[async_trait::async_trait(?Send)]
+impl<T> PrivateKeyRepo for Rc<T>
+where
+    T: PrivateKeyRepo,
+{
+    type Error = T::Error;
+
+    async fn store(
+        &self,
+        actor_id: Url,
+        key_id: KeyId,
+        private_key_pem: String,
+    ) -> Result<(), Self::Error> {
+        T::store(self, actor_id, key_id, private_key_pem).await
+    }
+
+    async fn fetch(&self, actor_id: &Url) -> Result<(KeyId, String), Self::Error> {
+        T::fetch(self, actor_id).await
+    }
+}
+
+#[async_trait::async_trait(?Send)]
+impl<T> PrivateKeyRepo for Arc<T>
+where
+    T: PrivateKeyRepo,
+{
+    type Error = T::Error;
+
+    async fn store(
+        &self,
+        actor_id: Url,
+        key_id: KeyId,
+        private_key_pem: String,
+    ) -> Result<(), Self::Error> {
+        T::store(self, actor_id, key_id, private_key_pem).await
+    }
+
+    async fn fetch(&self, actor_id: &Url) -> Result<(KeyId, String), Self::Error> {
+        T::fetch(self, actor_id).await
+    }
+}