diff --git a/crates/runner-opentitan/src/board/crypto.rs b/crates/runner-opentitan/src/board/crypto.rs
index d8bd3dc75..83229edab 100644
--- a/crates/runner-opentitan/src/board/crypto.rs
+++ b/crates/runner-opentitan/src/board/crypto.rs
@@ -16,7 +16,7 @@ use wasefire_board_api::crypto;
 use wasefire_error::{Code, Error};
 
 mod aes;
-mod ecdh;
+pub mod ecdh;
 mod ecdsa;
 #[cfg(feature = "ed25519")]
 mod ed25519;
diff --git a/crates/runner-opentitan/src/board/crypto/ecdh.rs b/crates/runner-opentitan/src/board/crypto/ecdh.rs
index 24be089f7..09eadcd13 100644
--- a/crates/runner-opentitan/src/board/crypto/ecdh.rs
+++ b/crates/runner-opentitan/src/board/crypto/ecdh.rs
@@ -90,7 +90,7 @@ impl Api<32> for Impl {
         key[.. 32].copy_from_slice(y);
         key[32 ..].copy_from_slice(x);
         key.reverse();
-        public.checksum = 0;
+        public.checksum = unsafe { public.borrow()? }.checksum();
         Ok(())
     }
 
@@ -107,6 +107,24 @@ impl Api<32> for Impl {
     }
 }
 
+#[cfg(feature = "test-vendor")]
+pub fn syscall(
+    memory: impl wasefire_board_api::applet::Memory, x: u32, y: u32, z: u32,
+) -> Result<u32, wasefire_board_api::Failure> {
+    match (x, y, z) {
+        // Update checksum of private key.
+        (1, ptr, 0) => {
+            let key = memory.get_mut(ptr, core::mem::size_of::<Private>() as u32)?;
+            let key = try_from_bytes_mut::<Private>(key)?;
+            key.checksum = unsafe { key.borrow()? }.checksum();
+            let key = &mut key.public;
+            key.checksum = unsafe { key.borrow()? }.checksum();
+            Ok(0)
+        }
+        _ => Err(wasefire_board_api::Failure::TRAP),
+    }
+}
+
 #[derive(Clone, Copy, bytemuck::Pod, bytemuck::Zeroable)]
 #[repr(C)]
 struct Public {
diff --git a/crates/runner-opentitan/src/board/crypto/ecdsa.rs b/crates/runner-opentitan/src/board/crypto/ecdsa.rs
index 36a183bc2..4e32160ce 100644
--- a/crates/runner-opentitan/src/board/crypto/ecdsa.rs
+++ b/crates/runner-opentitan/src/board/crypto/ecdsa.rs
@@ -114,7 +114,7 @@ impl Api<32> for Impl {
         key[.. 32].copy_from_slice(y);
         key[32 ..].copy_from_slice(x);
         key.reverse();
-        public.checksum = 0;
+        public.checksum = unsafe { public.borrow()? }.checksum();
         Ok(())
     }
 }
diff --git a/crates/runner-opentitan/src/board/vendor.rs b/crates/runner-opentitan/src/board/vendor.rs
index 652328efc..62cde96a0 100644
--- a/crates/runner-opentitan/src/board/vendor.rs
+++ b/crates/runner-opentitan/src/board/vendor.rs
@@ -39,6 +39,7 @@ impl Api for Impl {
                 let push = |event| state.events.push(Event(event).into());
                 syscall_test::syscall(memory, handlers, push, x2, x3, x4)
             }),
+            (0x80000001, x, y, z) => crate::board::crypto::ecdh::syscall(memory, x, y, z),
             _ => Err(Failure::TRAP),
         }
     }
diff --git a/crates/runner-opentitan/src/crypto/common.rs b/crates/runner-opentitan/src/crypto/common.rs
index fc4fd80ed..1bf6a88eb 100644
--- a/crates/runner-opentitan/src/crypto/common.rs
+++ b/crates/runner-opentitan/src/crypto/common.rs
@@ -284,6 +284,10 @@ impl UnblindedKey {
         unsafe { core::slice::from_raw_parts(self.key, self.key_length / 4) }
     }
 
+    pub fn checksum(&self) -> u32 {
+        unsafe { integrity_unblinded_checksum(self) }
+    }
+
     fn layout(key_length: usize) -> Result<Layout, Error> {
         Layout::from_size_align(key_length, 4).map_err(|_| Error::user(Code::InvalidArgument))
     }
@@ -337,6 +341,11 @@ impl BlindedKey {
         unsafe { core::slice::from_raw_parts(self.keyblob, self.keyblob_length / 4) }
     }
 
+    #[cfg(feature = "test-vendor")]
+    pub fn checksum(&self) -> u32 {
+        unsafe { integrity_blinded_checksum(self) }
+    }
+
     fn layout(keyblob_length: usize) -> Result<Layout, Error> {
         Layout::from_size_align(keyblob_length, 4).map_err(|_| Error::user(Code::InvalidArgument))
     }
@@ -377,4 +386,7 @@ unsafe extern "C" {
     fn otcrypto_import_blinded_key(
         share0: ConstWord32Buf, share1: ConstWord32Buf, key: *mut BlindedKey,
     ) -> i32;
+    fn integrity_unblinded_checksum(key: *const UnblindedKey) -> u32;
+    #[cfg(feature = "test-vendor")]
+    fn integrity_blinded_checksum(key: *const BlindedKey) -> u32;
 }
diff --git a/crates/runner-opentitan/src/error.rs b/crates/runner-opentitan/src/error.rs
index bff996e0b..08457bc84 100644
--- a/crates/runner-opentitan/src/error.rs
+++ b/crates/runner-opentitan/src/error.rs
@@ -42,5 +42,5 @@ pub fn unwrap_status(mut x: i32) -> Result<i32, Error> {
 #[cfg(false)]
 #[unsafe(no_mangle)]
 extern "C" fn wasefire_debug_mark(mark: i32) {
-    wasefire_logger::error!("DEBUG MARK {}", mark);
+    wasefire_logger::error!("DEBUG MARK {:08x} {}", mark, mark);
 }
diff --git a/examples/rust/ecdh_test/src/lib.rs b/examples/rust/ecdh_test/src/lib.rs
index b5fd4683f..d1739b31b 100644
--- a/examples/rust/ecdh_test/src/lib.rs
+++ b/examples/rust/ecdh_test/src/lib.rs
@@ -17,6 +17,7 @@
 #![no_std]
 wasefire::applet!();
 
+use alloc::borrow::Cow;
 use alloc::vec;
 
 use ecdh_vectors::{P256_VECTORS, P384_VECTORS, Vector};
@@ -61,11 +62,15 @@ fn test<C: Curve>(name: &str, vectors: &[Vector]) {
     }
     for &Vector { tc_id, private, otprivate, public_x, public_y, shared } in vectors {
         debug!("- {tc_id}");
-        let private = match () {
-            () if cfg!(feature = "runner-opentitan") => otprivate,
-            _ => private,
+        let private: Cow<[u8]> = match () {
+            () if cfg!(feature = "runner-opentitan") => {
+                let mut private = otprivate.to_vec();
+                unsafe { vendor::syscall(0x80000001, 1, private.as_mut_ptr().addr(), 0) }.unwrap();
+                private.into()
+            }
+            _ => private.into(),
         };
-        let private = Private::<C>::import_testonly(private).unwrap();
+        let private = Private::<C>::import_testonly(&private).unwrap();
         let public = Public::<C>::import(public_x, public_y).unwrap();
         let shared_ = Shared::<C>::new(&private, &public).unwrap();
         let mut actual = vec![0; C::SIZE];