Add support for using external signing application and .pem private key files to vbutil_keyblock.

host/include/host_signature.h

 /* Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  *
  * Host-side functions for verified boot.
  */
 
 #ifndef VBOOT_REFERENCE_HOST_SIGNATURE_H_
 #define VBOOT_REFERENCE_HOST_SIGNATURE_H_
 
@@ skipping 14 matching lines @@
 
 /* Copy a signature key from [src] to [dest].
  *
  * Returns 0 if success, non-zero if error. */
 int SignatureCopy(VbSignature* dest, const VbSignature* src);
 
 
 /* Calculates a SHA-512 checksum.
  * Caller owns the returned pointer, and must free it with Free().
  *
- * Returns NULL if error. */
+ * Returns NULL on error. */
 VbSignature* CalculateChecksum(const uint8_t* data, uint64_t size);
 
 
 /* Calculates a signature for the data using the specified key.
  * Caller owns the returned pointer, and must free it with Free().
  *
- * Returns NULL if error. */
+ * Returns NULL on error. */
 VbSignature* CalculateSignature(const uint8_t* data, uint64_t size,
                                 const VbPrivateKey* key);
 
+/* Calculates a signature for the data using the specified key and
+ * an external program.
+ * Caller owns the returned pointer, and must free it with Free().
+ *
+ * Returns NULL on error. */
+VbSignature* CalculateSignature_external(const uint8_t* data, uint64_t size,
+                                         const char* key_file,
+                                         uint64_t key_algorithm,
+                                         const char* external_signer);
+
 #endif  /* VBOOT_REFERENCE_HOST_SIGNATURE_H_ */