The smallest signature sizes that I can find are for elliptic curve public key systems where the signature is 4 times the security level (2 x the key size). In my case I can change the key every day, after which it is OK if the key is revealed.
So my questions are:
- is there a more efficient signature than 2 x key size?
- what would be the minimal acceptable key size for implementations over the next 10 years or so. Looking at a table of key size vs. operations to crack I get a 108 bit ECC key requires 1.8 x 10^8 MIPS, but I'm not sure how to interpret MIPS these days when graphics processors are so powerful. Is 1.8 x 10^8 MIPS a lot of compute power?