Vboot Reference: Add the "real" reference firmware verification function (VerifyFirmware).

src/platform/vboot_reference/include/file_keys.h

Index: src/platform/vboot_reference/include/file_keys.h
diff --git a/src/platform/vboot_reference/include/file_keys.h b/src/platform/vboot_reference/include/file_keys.h
index 9236172bbbeae95b5bd0b9c5b174abfe6486afca..46735ece1f0c9e129affd8549eaadf5d8b246b8e 100644
--- a/src/platform/vboot_reference/include/file_keys.h
+++ b/src/platform/vboot_reference/include/file_keys.h
@@ -25,4 +25,12 @@ uint8_t* BufferFromFile(char* input_file, int* len);
  */
 RSAPublicKey* RSAPublicKeyFromFile(char* input_file);
 
+/* Helper function to invoke external program to calculate signature on
+ * [input_file] using private key [key_file] and signature algorithm
+ * [algorithm].
+ *
+ * Returns the signature. Caller owns the buffer and must Free() it.
+ */
+uint8_t* SignatureFile(char* input_fie, char* key_file, int algorithm);
+
 #endif  /* VBOOT_REFERENCE_FILE_KEYS_H_ */