Veriiable Escrowed Signature

We combine a publicly veriiable encryption technique and a Schnorr type signature scheme to achieve a veriiable escrowed signature scheme. The scheme allows a signer to convince a veriier the validity of a signature without letting him see the signature value. The unavailable but veriiable signature is encrypted under a public key of someone (e.g., a trusted third party) who stays oo-line. The technique will have useful applications in such as fair exchange of contracts between two untrusted parties without using on-line help of a commonly trusted third party, and fair escrow cryptosystems using oo-line escrow agents.