Check all ESP padding bytes during unpad

1 files changed, 11 insertions, 12 deletions

diff --git a/src/lib/modes/mode_pad/mode_pad.cpp b/src/lib/modes/mode_pad/mode_pad.cpp
index 6550edef2..d4ab914cc 100644
--- a/src/lib/modes/mode_pad/mode_pad.cpp
+++ b/src/lib/modes/mode_pad/mode_pad.cpp
@@ -145,23 +145,22 @@ void ESP_Padding::add_padding(secure_vector<byte>& buffer,
 */
 size_t ESP_Padding::unpad(const byte block[], size_t size) const
    {
-   while(size)
+   byte last_byte = block[size-1];
+   if(last_byte > size)
       {
-      if(block[size-1] == 0x01)
-         {
-         break;
-         }
-      if(block[size-1] == 0x00)
+      throw Decoding_Error(name());
+      }
+
+   size_t i = size - 1;
+   while(i > size - last_byte)
+      {
+      if(block[i-1] != block[i]-1)
          {
          throw Decoding_Error(name());
          }
-      size--;
+      --i;
       }
-   if(!size)
-      {
-      throw Decoding_Error(name());
-      }
-   return (size-1);
+   return i;
    }