diff --git a/src/lib.rs b/src/lib.rs
index 0cd7f3a..40cfd72 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -31,5 +31,91 @@ mod manager;
 mod runloop;
 pub mod u2fprotocol;
 
+use std::ptr;
+
 pub use u2fprotocol::*;
 pub use manager::U2FManager as U2FManager;
+
+#[no_mangle]
+pub extern "C" fn rust_u2f_mgr_new() -> *mut U2FManager {
+    let manager = U2FManager::new();
+    Box::into_raw(Box::new(manager))
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn rust_u2f_mgr_free(ptr: *mut U2FManager) {
+    if !ptr.is_null() {
+        Box::from_raw(ptr);
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn rust_u2f_mgr_register(ptr: *mut U2FManager,
+                                               timeout: u64,
+                                               challenge_ptr: *const u8,
+                                               challenge_len: usize,
+                                               application_ptr: *const u8,
+                                               application_len: usize,
+                                               registration_ptr: *mut u8,
+                                               registration_len: *mut usize,
+                                               max_registration_len: usize) {
+    if ptr.is_null() {
+        return; // TODO error
+    }
+
+    let mut mgr = Box::from_raw(ptr);
+    let challenge = std::slice::from_raw_parts(challenge_ptr, challenge_len);
+    let application = std::slice::from_raw_parts(application_ptr, application_len);
+
+    let res = mgr.register(timeout, challenge.to_vec(), application.to_vec());
+    let _ = Box::into_raw(mgr);
+
+    let res = match res {
+        Ok(rv) => rv,
+        _ => return // TODO error
+    };
+
+    if res.len() > max_registration_len {
+      return; // TODO error
+    }
+
+    *registration_len = res.len();
+    ptr::copy_nonoverlapping(res.as_ptr(), registration_ptr, res.len());
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn rust_u2f_mgr_sign(ptr: *mut U2FManager,
+                                           timeout: u64,
+                                           challenge_ptr: *const u8,
+                                           challenge_len: usize,
+                                           application_ptr: *const u8,
+                                           application_len: usize,
+                                           key_handle_ptr: *const u8,
+                                           key_handle_len: usize,
+                                           signature_ptr: *mut u8,
+                                           signature_len: *mut usize,
+                                           max_signature_len: usize) {
+    if ptr.is_null() {
+        return; // TODO error
+    }
+
+    let mut mgr = Box::from_raw(ptr);
+    let challenge = std::slice::from_raw_parts(challenge_ptr, challenge_len);
+    let application = std::slice::from_raw_parts(application_ptr, application_len);
+    let key_handle = std::slice::from_raw_parts(key_handle_ptr, key_handle_len);
+
+    let sig = mgr.sign(timeout, challenge.to_vec(), application.to_vec(), key_handle.to_vec());
+    let _ = Box::into_raw(mgr);
+
+    let sig = match sig {
+        Ok(rv) => rv,
+        _ => return // TODO error
+    };
+
+    if sig.len() > max_signature_len {
+      return; // TODO error
+    }
+
+    *signature_len = sig.len();
+    ptr::copy_nonoverlapping(sig.as_ptr(), signature_ptr, sig.len());
+}
diff --git a/src/u2fhid-capi.h b/src/u2fhid-capi.h
new file mode 100644
index 0000000..e22594c
--- /dev/null
+++ b/src/u2fhid-capi.h
@@ -0,0 +1,35 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef __U2FHID_CAPI
+#define __U2FHID_CAPI
+#include <stdlib.h>
+#include "nsString.h"
+
+extern "C" {
+
+// NOTE: Preconditions
+// * All rust_u2f_mgr* pointers must refer to pointers which are returned
+//   by rust_u2f_mgr_new, and must be freed with rust_u2f_mgr_free.
+
+// The `rust_u2f_mgr` opaque type is equivalent to the rust type `::manager::U2FManager`
+struct rust_u2f_mgr;
+
+rust_u2f_mgr* rust_u2f_mgr_new();
+/* unsafe */ void rust_u2f_mgr_free(rust_u2f_mgr* mgr);
+
+void rust_u2f_mgr_register(rust_u2f_mgr* mgr, uint64_t timeout,
+                           const uint8_t* challenge_ptr, size_t challenge_len,
+                           const uint8_t* application_ptr, size_t application_len,
+                           uint8_t* registration_ptr, size_t* registration_len, size_t max_registration_len);
+
+void rust_u2f_mgr_sign(rust_u2f_mgr* mgr, uint64_t timeout,
+                       const uint8_t* challenge_ptr, size_t challenge_len,
+                       const uint8_t* application_ptr, size_t application_len,
+                       const uint8_t* key_handle_ptr, size_t key_handle_len,
+                       uint8_t* signature_ptr, size_t* signature_len, size_t max_signature_len);
+
+}
+
+#endif // __U2FHID_CAPI