In my application I want to use Rabin crypto system with short keys (like 128 bits) and MD5 for hashing. I found that schema like PKCS1-V1_5 or PPS does not allow you to have such small keys and result signature is like 64 bytes for 512 bit key.
I need to sign small amount of data like 30-50 bytes and having 64 bytes signature is noticeable overhead. I tried BLS (48 bytes for signature) but it is too slow compared to Rabin.
My idea is to use MD5 because it needs only 128 bits and short key with same size to avoid padding. So in this case I don't need schema. Also this should give me 20 bytes for each signature. I realise that this is very weak signature but data (packet) lifetime will be short.
Will such approach work?