From 13128351027d9163b529a6dc5c8674c6e9635d09 Mon Sep 17 00:00:00 2001
From: kaihs <>
Date: Sun, 18 Nov 2018 15:44:03 +0000
Subject: [PATCH] WMBus: error correction for AES descryption (no padding if
 data length is multiple of block size)

git-svn-id: https://svn.fhem.de/fhem/trunk@17777 2b470e98-0d58-463d-a4d8-8e2adae1ed80
---
 fhem/FHEM/WMBus.pm | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/fhem/FHEM/WMBus.pm b/fhem/FHEM/WMBus.pm
index 891e7902a..0aa0e98c7 100644
--- a/fhem/FHEM/WMBus.pm
+++ b/fhem/FHEM/WMBus.pm
@@ -1443,13 +1443,20 @@ sub decodePayload($$) {
 sub decrypt($) {
   my $self = shift;
   my $encrypted = shift;
+  my $padding = 2;
   
   # see 4.2.5.3, page 26      
   my $initVector = substr($self->{msg},2,8);
   for (1..8) {
     $initVector .= pack('C',$self->{access_no});
   }
-  my $cipher = Crypt::Mode::CBC->new('AES', 2);
+  if (length($encrypted)%16 == 0) {
+    # no padding if data length is multiple of blocksize
+    $padding = 0;
+  } else {
+    $padding = 2;
+  }
+  my $cipher = Crypt::Mode::CBC->new('AES', $padding);
   return $cipher->decrypt($encrypted, $self->{aeskey}, $initVector);
 }
 
@@ -1817,6 +1824,7 @@ sub decodeApplicationLayer($) {
 
     if ($self->{aeskey}) { 
       if ($hasCBC) {
+        #printf("encrypted payload %s\n", unpack("H*", substr($applicationlayer,$offset)));
         $payload = $self->decrypt(substr($applicationlayer,$offset));
         #printf("decrypted payload %s\n", unpack("H*", $payload));
         if (unpack('n', $payload) == 0x2f2f) {