diff --git a/common/src/types.rs b/common/src/types.rs
index ad091d2..a57cc3a 100644
--- a/common/src/types.rs
+++ b/common/src/types.rs
@@ -1,20 +1,47 @@
 use serde::{Deserialize, Serialize};
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[derive(
+    Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, zvariant::Type,
+)]
 #[serde(rename_all = "lowercase")]
+#[zvariant(signature = "s")]
 pub enum Mode {
     Disabled,
     Optional,
     Required,
 }
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[derive(
+    Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize, zvariant::Type,
+)]
 #[serde(rename_all = "lowercase")]
+#[zvariant(signature = "s")]
 pub enum Method {
     Fido2,
     Totp,
 }
 
+#[derive(
+    Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize, zvariant::Type,
+)]
+#[serde(rename_all = "lowercase")]
+#[zvariant(signature = "s")]
+pub enum Transport {
+    Usb,
+    Nfc,
+    Internal,
+    Unknown,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, zvariant::Type)]
+pub struct Credential {
+    pub id: String,
+    pub nickname: String,
+    pub method: Method,
+    pub transport: Transport,
+    pub created_unix: u64,
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -32,4 +59,18 @@ mod tests {
         let s = serde_json::to_string(&m).unwrap();
         assert_eq!(s, "\"fido2\"");
     }
+
+    #[test]
+    fn credential_roundtrips_via_serde() {
+        let c = Credential {
+            id: "abc123".to_string(),
+            nickname: "Yellow Yubikey".to_string(),
+            method: Method::Fido2,
+            transport: Transport::Usb,
+            created_unix: 1_700_000_000,
+        };
+        let json = serde_json::to_string(&c).unwrap();
+        let back: Credential = serde_json::from_str(&json).unwrap();
+        assert_eq!(c, back);
+    }
 }