diff --git a/src/main/java/com/uid2/admin/model/CloudEncryptionKeySummary.java b/src/main/java/com/uid2/admin/model/CloudEncryptionKeySummary.java
index 89ef734d..a3c987b5 100644
--- a/src/main/java/com/uid2/admin/model/CloudEncryptionKeySummary.java
+++ b/src/main/java/com/uid2/admin/model/CloudEncryptionKeySummary.java
@@ -3,13 +3,24 @@
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.uid2.shared.model.CloudEncryptionKey;
 
+import java.time.Instant;
+
 public record CloudEncryptionKeySummary(
-    @JsonProperty int id,
-    @JsonProperty int siteId,
-    @JsonProperty long activates,
-    @JsonProperty long created
+        @JsonProperty int id,
+        @JsonProperty int siteId,
+        @JsonProperty String activates,
+        @JsonProperty String created
 ) {
     public static CloudEncryptionKeySummary fromFullKey(CloudEncryptionKey key) {
-        return new CloudEncryptionKeySummary(key.getId(), key.getSiteId(), key.getActivates(), key.getCreated());
+        return new CloudEncryptionKeySummary(
+                key.getId(),
+                key.getSiteId(),
+                toIsoTimestamp(key.getActivates()),
+                toIsoTimestamp(key.getCreated())
+        );
+    }
+
+    private static String toIsoTimestamp(Long epochSeconds) {
+        return Instant.ofEpochSecond(epochSeconds).toString();
     }
 }
diff --git a/src/test/java/com/uid2/admin/vertx/CloudEncryptionKeyServiceTest.java b/src/test/java/com/uid2/admin/vertx/CloudEncryptionKeyServiceTest.java
index 0adb109e..29ec58de 100644
--- a/src/test/java/com/uid2/admin/vertx/CloudEncryptionKeyServiceTest.java
+++ b/src/test/java/com/uid2/admin/vertx/CloudEncryptionKeyServiceTest.java
@@ -53,14 +53,19 @@ public void testList_noAccess(Vertx vertx, VertxTestContext testContext) {
     public void testList_withKeys(Vertx vertx, VertxTestContext testContext) {
         fakeAuth(Role.MAINTAINER);
 
-        CloudEncryptionKey key1 = new CloudEncryptionKey(1, 2, 100, 100, "secret 1");
-        CloudEncryptionKey key2 = new CloudEncryptionKey(2, 2, 200, 100, "secret 2");
+        var date1EpochSeconds = 100;
+        var date2EpochSeconds = 200;
+        var date1Iso = "1970-01-01T00:01:40Z";
+        var date2Iso = "1970-01-01T00:03:20Z";
+
+        CloudEncryptionKey key1 = new CloudEncryptionKey(1, 2, date1EpochSeconds, date1EpochSeconds, "secret 1");
+        CloudEncryptionKey key2 = new CloudEncryptionKey(2, 2, date2EpochSeconds, date1EpochSeconds, "secret 2");
 
         setCloudEncryptionKeys(key1, key2);
 
         var expected = new CloudEncryptionKeyListResponse(List.of(
-                new CloudEncryptionKeySummary(1, 2, 100, 100),
-                new CloudEncryptionKeySummary(2, 2, 200, 100)
+                new CloudEncryptionKeySummary(1, 2, date1Iso, date1Iso),
+                new CloudEncryptionKeySummary(2, 2, date2Iso, date1Iso)
         ));
 
         get(vertx, testContext, Endpoints.CLOUD_ENCRYPTION_KEY_LIST, response -> {