Add function for generating validation signatures.

src/trusted/validator/caching/hashing_interface.h

Index: src/trusted/validator/caching/hashing_interface.h
diff --git a/src/trusted/validator/caching/hashing_interface.h b/src/trusted/validator/caching/hashing_interface.h
new file mode 100644
index 0000000000000000000000000000000000000000..1fbf45b2b0c459a6dc8f4d92004f7973309fd25a
--- /dev/null
+++ b/src/trusted/validator/caching/hashing_interface.h
@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2012 The Native Client Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef NATIVE_CLIENT_SRC_TRUSTED_VALIDATOR_CACHING_HASHING_INTERFACE_H_
+#define NATIVE_CLIENT_SRC_TRUSTED_VALIDATOR_CACHING_HASHING_INTERFACE_H_
+
+#include "native_client/src/include/nacl_base.h"
+
+EXTERN_C_BEGIN
+
+struct HashingInterface {
+  void *(*create)(const unsigned char *key, const unsigned int length);
+  void (*update)(void *ctx, const unsigned char *data,
+                 const unsigned int length);
+  void (*digest)(void *ctx, unsigned char *data, unsigned int *length,
+                 const unsigned int max_length);
+};
+
+EXTERN_C_END
+
+#endif /* NATIVE_CLIENT_SRC_TRUSTED_VALIDATOR_CACHING_HASHING_INTERFACE_H_ */