||The conventional digital signature is implemented and operated as the function of registered stamp or signature for digital documents. In the real world, however, it is rare to use registered stamps or signatures, and non-registered ones are more used often. If it is possible to apply non-registered stamp/signature system to digital world, it is expected that digital signature will become more useful and effective. To achieve this, it is vital to ensure that “the signing key is not registered, but still repudiation is prevented”. So, we propose to combine digital signature and biometric signature to connect signing key and signer with each other. Thus, a non-registered digital signature, Lazy Signature, is realized in this paper.