diff --git a/services/identity/src/database.rs b/services/identity/src/database.rs
--- a/services/identity/src/database.rs
+++ b/services/identity/src/database.rs
@@ -441,6 +441,30 @@
       .await
       .map_err(|e| Error::AwsSdk(e.into()))
   }
+
+  pub async fn get_users(&self) -> Result<Vec<String>, Error> {
+    let scan_output = self
+      .client
+      .scan()
+      .table_name(USERS_TABLE)
+      .projection_expression(USERS_TABLE_PARTITION_KEY)
+      .send()
+      .await
+      .map_err(|e| Error::AwsSdk(e.into()))?;
+
+    let mut result = Vec::new();
+    if let Some(attributes) = scan_output.items {
+      for mut attribute in attributes {
+        let id = parse_string_attribute(
+          USERS_TABLE_PARTITION_KEY,
+          attribute.remove(USERS_TABLE_PARTITION_KEY),
+        )
+        .map_err(Error::Attribute)?;
+        result.push(id);
+      }
+    }
+    Ok(result)
+  }
 }
 
 #[derive(
diff --git a/services/identity/src/service.rs b/services/identity/src/service.rs
--- a/services/identity/src/service.rs
+++ b/services/identity/src/service.rs
@@ -13,6 +13,7 @@
 use rand::rngs::OsRng;
 use rand::{CryptoRng, Rng};
 use siwe::Message;
+use std::collections::HashSet;
 use std::pin::Pin;
 use tokio::sync::mpsc;
 use tokio_stream::{wrappers::ReceiverStream, StreamExt};
@@ -40,10 +41,11 @@
   registration_request::Data::PakeRegistrationRequestAndUserId,
   registration_request::Data::PakeRegistrationUploadAndCredentialRequest,
   registration_response::Data::PakeLoginResponse as PakeRegistrationLoginResponse,
-  registration_response::Data::PakeRegistrationResponse, DeleteUserRequest,
-  DeleteUserResponse, GetUserIdRequest, GetUserIdResponse,
-  GetUserPublicKeyRequest, GetUserPublicKeyResponse, LoginRequest,
-  LoginResponse, PakeLoginRequest as PakeLoginRequestStruct,
+  registration_response::Data::PakeRegistrationResponse, CompareUsersRequest,
+  CompareUsersResponse, DeleteUserRequest, DeleteUserResponse,
+  GetUserIdRequest, GetUserIdResponse, GetUserPublicKeyRequest,
+  GetUserPublicKeyResponse, LoginRequest, LoginResponse,
+  PakeLoginRequest as PakeLoginRequestStruct,
   PakeLoginResponse as PakeLoginResponseStruct, RegistrationRequest,
   RegistrationResponse, VerifyUserTokenRequest, VerifyUserTokenResponse,
   WalletLoginRequest as WalletLoginRequestStruct,
@@ -244,6 +246,29 @@
       Err(e) => Err(handle_db_error(e)),
     }
   }
+
+  #[instrument(skip(self))]
+  async fn compare_users(
+    &self,
+    request: Request<CompareUsersRequest>,
+  ) -> Result<Response<CompareUsersResponse>, Status> {
+    let message = request.into_inner();
+    let mut mysql_users_vec = message.users;
+    let mut ddb_users_vec = match self.client.get_users().await {
+      Ok(user_list) => user_list,
+      Err(e) => return Err(handle_db_error(e)),
+    };
+    // We use HashSets here for faster lookups
+    let mysql_users_set = HashSet::<String>::from_iter(mysql_users_vec.clone());
+    let ddb_users_set = HashSet::<String>::from_iter(ddb_users_vec.clone());
+
+    ddb_users_vec.retain(|user| !mysql_users_set.contains(user));
+    mysql_users_vec.retain(|user| !ddb_users_set.contains(user));
+    Ok(Response::new(CompareUsersResponse {
+      users_missing_from_keyserver: ddb_users_vec,
+      users_missing_from_identity: mysql_users_vec,
+    }))
+  }
 }
 
 async fn put_token_helper(
diff --git a/shared/protos/identity.proto b/shared/protos/identity.proto
--- a/shared/protos/identity.proto
+++ b/shared/protos/identity.proto
@@ -20,6 +20,10 @@
     (GetUserPublicKeyResponse) {}
 
   rpc DeleteUser(DeleteUserRequest) returns (DeleteUserResponse) {}
+  // Called by Ashoat's keyserver with a list of user IDs in MySQL and returns:
+  // 1. a list of user IDs that are in DynamoDB but not in the supplied list
+  // 2. a list of user IDs that are in the supplied list but not in DynamoDB
+  rpc CompareUsers(CompareUsersRequest) returns (CompareUsersResponse) {}
 }
 
 // Helper types
@@ -165,3 +169,14 @@
 // Need to respond with a message to show success, an
 // empty reponse should work just fine
 message DeleteUserResponse {}
+
+// CompareUsers
+
+message CompareUsersRequest {
+  repeated string users = 1;
+}
+
+message CompareUsersResponse {
+  repeated string usersMissingFromKeyserver = 1;
+  repeated string usersMissingFromIdentity = 2;
+}