Obfuscating EVES Algorithm and Its Application in Fair Electronic Transactions in Public Clouds

In EUROCRYPT' 10, Hada proposed a secure obfuscator of encrypted signature scheme which can be executed on an untrusted server to solve the security problem of untrusted proxy signature. In Hada's scheme, the server can generate a valid signature for the user without obtaining user's secret key; however, the scheme cannot resist the collusion attack. In this paper, we extend the study of encrypted signature schemes and propose an obfuscator for encrypted verifiable encrypted signature (EVES), andmodel the application in electronic transactions. The proposed scheme cannot only prevent the semihonest server from obtaining user's sensitive information, but also resist to the collusion activities between verifier/receiver and untrusted cloud. We show that the obfuscation scheme achieves the requirement of virtual black-box security under standard cryptographic assumptions. The experiments show that the time of constructing the EVES obfuscator is 63 ms, the signing time of the obfuscated algorithm is 78 ms, and the verifying time of obfuscated signature is 63 ms, which is more efficient and practical than related schemes, and the scheme can be deployed in scenarios requiring electronic transactions in outsourced clouds.