Fix challenge length handling, Fix #63

src/gpg_challenge.c

@@ -27,7 +27,7 @@ int gpg_apdu_get_challenge() {
   } else {
     olen = G_gpg_vstate.io_le;
   }
-  if (olen > GPG_EXT_CHALLENGE_LENTH) {
+  if (olen == 0 || olen > GPG_EXT_CHALLENGE_LENTH) {
     THROW(SW_WRONG_LENGTH);
     return SW_WRONG_LENGTH;
   }

src/gpg_io.c

@@ -306,6 +306,7 @@ int gpg_io_do(unsigned int io_flags) {
 
   case INS_GET_CHALLENGE:
     if (G_gpg_vstate.io_p1 == 0) {
+      G_gpg_vstate.io_le = G_io_apdu_buffer[4];
       break;
     }