diff --git a/Keymaster.h b/Keymaster.h
index 4bc0df7..dc6f1bc 100644
--- a/Keymaster.h
+++ b/Keymaster.h
@@ -19,6 +19,8 @@
 
 #ifdef __cplusplus
 
+#include "KeyBuffer.h"
+
 #include <memory>
 #include <string>
 #include <utility>
@@ -51,7 +53,14 @@
     ErrorCode errorCode() { return mError; }
     // Call "update" repeatedly until all of the input is consumed, and
     // concatenate the output. Return true on success.
-    bool updateCompletely(const std::string& input, std::string* output);
+    template <class TI, class TO>
+    bool updateCompletely(TI& input, TO* output) {
+        if (output) output->clear();
+        return updateCompletely(input.data(), input.size(), [&](const char* b, size_t n) {
+            if (output) std::copy(b, b+n, std::back_inserter(*output));
+        });
+    }
+
     // Finish and write the output to this string, unless pointer is null.
     bool finish(std::string* output);
     // Move constructor
@@ -80,6 +89,10 @@
     KeymasterOperation(ErrorCode error)
         : mDevice{nullptr}, mOpHandle{0},
           mError {error} {}
+
+    bool updateCompletely(const char* input, size_t inputLen,
+                          const std::function<void(const char*, size_t)> consumer);
+
     sp<IKeymasterDevice> mDevice;
     uint64_t mOpHandle;
     ErrorCode mError;