[rkp] Build MACed public key from boringssl EC_KEY

The secret will be added in a subsequent after we get the DICE
chain info of the RKP VM.

Bug: 300068317
Test: atest rialto_test
Change-Id: Ia373930fc8f1c6d38349208ca62b9b71b98d126f
diff --git a/rialto/tests/test.rs b/rialto/tests/test.rs
index b8ced95..e975bbf 100644
--- a/rialto/tests/test.rs
+++ b/rialto/tests/test.rs
@@ -75,11 +75,18 @@
     info!("Received response: {response:?}.");
 
     match response {
-        Response::GenerateEcdsaP256KeyPair(EcdsaP256KeyPair { .. }) => Ok(()),
+        Response::GenerateEcdsaP256KeyPair(EcdsaP256KeyPair { maced_public_key, .. }) => {
+            assert_array_has_nonzero(&maced_public_key[..]);
+            Ok(())
+        }
         _ => bail!("Incorrect response type"),
     }
 }
 
+fn assert_array_has_nonzero(v: &[u8]) {
+    assert!(v.iter().any(|&x| x != 0))
+}
+
 fn check_processing_generating_certificate_request(vm: &mut ServiceVm) -> Result<()> {
     let params = GenerateCertificateRequestParams { keys_to_sign: vec![], challenge: vec![] };
     let request = Request::GenerateCertificateRequest(params);