I am using hash for authenticating the signature of the message. since the hash will be part of a url that is used for QR code, I would like to keep the hash as short as possible in order to generate a less complicated qr code which is easy to scan.
Now I am using md5 hmac to compute the hash which already generates a shorter one(32) than SHA256. But it isn't short enough and I am thinking of truncating the hash to get a even shorter one. say length of 16.
I would like to get your opinion on how is this method, does it make the hash easily cracked practically? or if there is better method?