use Digest::MD5 qw(md5_hex);

$buffer = "\x01\x02Test";
$checksum = md5_hex($buffer);

$transfer_data = $checksum . $buffer;
...
# Daten senden
...
...
...

# Datenempfang
$receive_data = .....;

$checksum = substr($receive_data,0,32);
$buffer = substr($receive_data,32);

if (md5_hex($buffer) ne $checksum ) {
   # falsche Prüfsumme
   # Übertragung nicht ok
   ....
}