Abstract The threshold cryptography provides a new approach to building intrusion toleranceapplications. In this paper, a threshold decryption scheme based elliptic curve cryptography is presented.A zero-knowledge test approach based on elliptic curve cryptography is designed. The application ofthese techniques in Web security is studied. Performance analysis shows that our scheme is characterizedby excellent security as well as high efficiency.Key words intrusion tolerance; elliptic curve cryptography; threshold decryption; websecurityDespite all the defenses, some of the attacks willinevitably be successful. We must build intrusiontolerant systems that can operate through these attacks.The threshold cryptography provides newmethodology for developing intrusion tolerance system.The research on the threshold cryptography basedintrusion tolerance techniques concentrate on thresholdencryption, threshold decryption, thresholdauthentication and threshold signature. Generally,threshold encryption and threshold decryption arebased on the cryptography algorithms, which arehomomorphic, such as RSA. The homomorpohicproperty is necessary in order to generate shares of thekey so that partial cryptograms can be combined into acryptogram for the correct message[1]. Therefore,nearly all projects studying on threshold cryptographytechniques focused on the homomorphic algorithm.Among these, the intrusion tolerance via thresholdcryptography (ITTC) project developed by StanfordUniversity is notable, which researched anddeveloped the intrusion tolerance application basedon threshold RSA[2].Currently, elliptic curve cryptography (ECC) isregarded as an attractive cryptography that canprovide greater strength, higher speed and smallerkeys than other cryptography systems[3,4]. Therefore,the research on threshold ECC deserves greatattention. However, ECC is not homomorphic. It isdifficult to design ECC-based threshold schemes. So,there are not many public published papers orreports on ECC-based threshold schemes, especiallyon ECC-based threshold encryption or decryptionschemes. In this paper, we present an ECC basedthreshold decryption scheme and a zero-knowledgetest approach. And we apply our research results inbuilding intrusion tolerant Web security system.