diff --git a/crates/alknet-core/src/endpoint.rs b/crates/alknet-core/src/endpoint.rs
index eb7070e..4dfc013 100644
--- a/crates/alknet-core/src/endpoint.rs
+++ b/crates/alknet-core/src/endpoint.rs
@@ -1581,6 +1581,7 @@ mod tests {
         let static_config = StaticConfig {
             listen_addr: None,
             tls_identity: Some(TlsIdentity::RawKey(sk)),
+            #[cfg(feature = "iroh")]
             iroh_relay: None,
             drain_timeout: Duration::from_millis(10),
         };
diff --git a/crates/alknet-core/src/lib.rs b/crates/alknet-core/src/lib.rs
index 9a3d9fc..29e3f71 100644
--- a/crates/alknet-core/src/lib.rs
+++ b/crates/alknet-core/src/lib.rs
@@ -9,4 +9,7 @@
 pub mod auth;
 pub mod config;
 pub mod endpoint;
+pub mod store;
 pub mod types;
+
+pub use store::{CredentialStore, EncryptedData, InMemoryCredentialStore, StoreError};
diff --git a/crates/alknet-core/src/store.rs b/crates/alknet-core/src/store.rs
new file mode 100644
index 0000000..417881e
--- /dev/null
+++ b/crates/alknet-core/src/store.rs
@@ -0,0 +1,203 @@
+//! Credential store: `CredentialStore` repo trait, `InMemoryCredentialStore`
+//! default adapter, `EncryptedData` core mirror, and the shared `StoreError`.
+//!
+//! See `docs/architecture/crates/core/auth.md` and ADR-031 / ADR-035 for the
+//! full specification. The store persists `EncryptedData` blobs keyed by
+//! provider; it never decrypts (ADR-025 — the vault is the sole decryption
+//! boundary).
+
+use std::collections::HashMap;
+use std::sync::RwLock;
+
+use async_trait::async_trait;
+
+#[non_exhaustive]
+#[derive(Debug, thiserror::Error)]
+pub enum StoreError {
+    #[error("backend error: {message}")]
+    Backend { message: String },
+    #[error("not found: {entity}")]
+    NotFound { entity: String },
+    #[error("serialization error: {message}")]
+    Serialization { message: String },
+}
+
+#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
+pub struct EncryptedData {
+    pub key_version: u32,
+    pub salt: Vec<u8>,
+    pub iv: Vec<u8>,
+    pub data: Vec<u8>,
+}
+
+#[async_trait]
+pub trait CredentialStore: Send + Sync {
+    fn get(&self, provider: &str) -> Option<EncryptedData>;
+    async fn put(&self, provider: &str, data: &EncryptedData) -> Result<(), StoreError>;
+    async fn delete(&self, provider: &str) -> Result<(), StoreError>;
+}
+
+pub struct InMemoryCredentialStore {
+    entries: RwLock<HashMap<String, EncryptedData>>,
+}
+
+impl InMemoryCredentialStore {
+    pub fn new() -> Self {
+        Self {
+            entries: RwLock::new(HashMap::new()),
+        }
+    }
+
+    pub fn with_entries(entries: HashMap<String, EncryptedData>) -> Self {
+        Self {
+            entries: RwLock::new(entries),
+        }
+    }
+}
+
+impl Default for InMemoryCredentialStore {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[async_trait]
+impl CredentialStore for InMemoryCredentialStore {
+    fn get(&self, provider: &str) -> Option<EncryptedData> {
+        let entries = self.entries.read().unwrap_or_else(|e| e.into_inner());
+        entries.get(provider).cloned()
+    }
+
+    async fn put(&self, provider: &str, data: &EncryptedData) -> Result<(), StoreError> {
+        let mut entries = self.entries.write().unwrap_or_else(|e| e.into_inner());
+        entries.insert(provider.to_string(), data.clone());
+        Ok(())
+    }
+
+    async fn delete(&self, provider: &str) -> Result<(), StoreError> {
+        let mut entries = self.entries.write().unwrap_or_else(|e| e.into_inner());
+        entries.remove(provider);
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn sample_encrypted_data() -> EncryptedData {
+        EncryptedData {
+            key_version: 2,
+            salt: vec![],
+            iv: vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12],
+            data: vec![0xde, 0xad, 0xbe, 0xef],
+        }
+    }
+
+    #[tokio::test]
+    async fn in_memory_get_put_delete_round_trip() {
+        let store = InMemoryCredentialStore::new();
+        let data = sample_encrypted_data();
+
+        assert!(store.get("openai").is_none());
+
+        store.put("openai", &data).await.unwrap();
+        let retrieved = store.get("openai").expect("provider should be present");
+        assert_eq!(retrieved.key_version, data.key_version);
+        assert_eq!(retrieved.salt, data.salt);
+        assert_eq!(retrieved.iv, data.iv);
+        assert_eq!(retrieved.data, data.data);
+
+        store.delete("openai").await.unwrap();
+        assert!(store.get("openai").is_none());
+    }
+
+    #[tokio::test]
+    async fn in_memory_get_returns_none_for_missing_provider() {
+        let store = InMemoryCredentialStore::new();
+        assert!(store.get("never-configured").is_none());
+    }
+
+    #[tokio::test]
+    async fn in_memory_delete_missing_provider_is_ok() {
+        let store = InMemoryCredentialStore::new();
+        store.delete("absent").await.unwrap();
+    }
+
+    #[tokio::test]
+    async fn in_memory_put_replaces_existing() {
+        let store = InMemoryCredentialStore::new();
+        let first = sample_encrypted_data();
+        let mut second = sample_encrypted_data();
+        second.data = vec![0xc0, 0xff, 0xee];
+
+        store.put("anthropic", &first).await.unwrap();
+        store.put("anthropic", &second).await.unwrap();
+
+        let retrieved = store.get("anthropic").expect("provider should be present");
+        assert_eq!(retrieved.data, second.data);
+    }
+
+    #[tokio::test]
+    async fn in_memory_with_entries_seeds_store() {
+        let mut entries = HashMap::new();
+        entries.insert("github".to_string(), sample_encrypted_data());
+        let store = InMemoryCredentialStore::with_entries(entries);
+
+        assert!(store.get("github").is_some());
+        assert!(store.get("openai").is_none());
+    }
+
+    #[test]
+    fn encrypted_data_serializes_and_deserializes_round_trip() {
+        let data = sample_encrypted_data();
+        let json = serde_json::to_string(&data).expect("serialize");
+        let decoded: EncryptedData = serde_json::from_str(&json).expect("deserialize");
+        assert_eq!(decoded.key_version, data.key_version);
+        assert_eq!(decoded.salt, data.salt);
+        assert_eq!(decoded.iv, data.iv);
+        assert_eq!(decoded.data, data.data);
+    }
+
+    #[test]
+    fn encrypted_data_round_trips_non_empty_salt() {
+        let data = EncryptedData {
+            key_version: 1,
+            salt: vec![0xab, 0xcd, 0xef],
+            iv: vec![0; 12],
+            data: vec![0x01, 0x02, 0x03],
+        };
+        let json = serde_json::to_string(&data).expect("serialize");
+        let decoded: EncryptedData = serde_json::from_str(&json).expect("deserialize");
+        assert_eq!(decoded.salt, data.salt);
+    }
+
+    #[test]
+    fn store_error_display_formatting() {
+        let backend = StoreError::Backend {
+            message: "disk full".to_string(),
+        };
+        assert_eq!(backend.to_string(), "backend error: disk full");
+
+        let not_found = StoreError::NotFound {
+            entity: "openai".to_string(),
+        };
+        assert_eq!(not_found.to_string(), "not found: openai");
+
+        let serialization = StoreError::Serialization {
+            message: "invalid utf8".to_string(),
+        };
+        assert_eq!(
+            serialization.to_string(),
+            "serialization error: invalid utf8"
+        );
+    }
+
+    #[test]
+    fn store_error_is_non_exhaustive() {
+        let err = StoreError::Backend {
+            message: "x".to_string(),
+        };
+        let _ = err.to_string();
+    }
+}