Ring signature

In this chapter, we discuss the basics of ring signature-a kind of anonymous signature that allows a user to sign on behalf of a self-formed group such that the verifier only knows that the signer is one of the users of this group but cannot find out the identification information (such as public key) of the real signer. We give the security model and a simple construction based on discrete logarithm setting. Then, we cover a variant called linkable ring signature, which provides linkability in addition to the property of a normal ring signature. Finally, we present a commercial application of (linkable) ring signature in blockchain called Ring Confidential Transaction (RingCT), which is the privacy-preserving protocol used in Monero, one of the largest cryptocurrencies in the world.