# Finding algorithm: desire RSA's uniqueness and ECDSA's space efficiency

I am asking for help in finding a signature algorithm with the following property:

1. Given a message m and a private key prikey, the result of signing m with prikey is unique (which is stricter than deterministic). In another word, there is only one signature (or finding another one using prikey is securely hard) that can pass the verification by the public key of prikey.
2. High space efficiency of storing private key and signature.

ECDSA's space efficiency is satisfying, but the signature is not unique; RSA has uniqueness, but is there any alternative with better space efficiency?

• ECDSA signatures can be made to enjoy the uniqueness property you require. See crypto.stackexchange.com/questions/851/… – Barack Obama Sep 17 '14 at 20:51
• @BarackObama Deterministic is not unique. – updogliu Sep 17 '14 at 21:17
• I think BLS is (or can be made) unique. Its signatures have half the size of ECDSA signatures. – CodesInChaos Sep 18 '14 at 9:18