Address some security concerns in the cgpt tool.

utility/vbutil_keyblock.c

Index: utility/vbutil_keyblock.c
diff --git a/utility/vbutil_keyblock.c b/utility/vbutil_keyblock.c
index dd13eb3df0482ff2866ed9e688ba129dfc26cb1b..ff1b44be456bc08c40d3c29e2d4d9a838c611845 100644
--- a/utility/vbutil_keyblock.c
+++ b/utility/vbutil_keyblock.c
@@ -127,7 +127,12 @@ static int Unpack(const char* infile, const char* datapubkey,
 
   /* If the block is signed, then verify it with the signing public key, since
      KeyBlockRead() only verified the hash. */
-  if (block->key_block_signature.sig_size && signpubkey) {
+  if (block->key_block_signature.sig_size) {
+    if (!signpubkey) {
+      fprintf(stderr,
+              "vbutil_keyblock: keyblock requires public key to verify\n");
+      return 1;
+    }
     sign_key = PublicKeyRead(signpubkey);
     if (!sign_key) {
       fprintf(stderr, "vbutil_keyblock: Error reading signpubkey.\n");
@@ -137,12 +142,16 @@ static int Unpack(const char* infile, const char* datapubkey,
       fprintf(stderr, "vbutil_keyblock: Error verifying key block.\n");
       return 1;
     }
+    printf("Signature algorithm:  %" PRIu64 " %s\n", sign_key->algorithm,
+           (sign_key->algorithm < kNumAlgorithms ?
+            algo_strings[sign_key->algorithm] : "(invalid)"));
     Free(sign_key);
+  } else {
+    printf("Signature Algorithm:  <none>\n");
   }
 
   printf("Key block file:       %s\n", infile);
-  printf("Signature             %s\n", sign_key ? "valid" : "ignored");
-  printf("Flags:                %" PRIu64 " ", block->key_block_flags);
+  printf("Flags:                %" PRIu64 "\n", block->key_block_flags);
   if (block->key_block_flags & KEY_BLOCK_FLAG_DEVELOPER_0)
     printf(" !DEV");
   if (block->key_block_flags & KEY_BLOCK_FLAG_DEVELOPER_1)