ABE has been widely applied for secure data protection in cloud computing. In ABE, userââ?¬â?¢s private keys are\ngenerated by attribute authority, thus, attribute authority has the ultimate privileges in the system and can\nimpersonate any users to forge valid signatures. Once the attribute authority become dishonest or be invaded in\ncloud systems, the systemââ?¬â?¢s security will be at risk. To better solve the problem mentioned above, in this paper, we\npropose a key-policy attribute based signature scheme with untrusted authority and traceability (KP-ABS-UT). In our\nscheme, the signerââ?¬â?¢s private key is composed by two components: one part is distributed by attribute authority and\nthe other part is chosen privately by the signerââ?¬â?¢s self. Thus attribute authority cannot forge any signatures which\nshould be signed by legal users. Besides, our scheme introduces an entity ââ?¬Å?tracerââ?¬Â, which can trace the identity of\nsigner when necessary. By security analysis and efficiency comparison, we prove our KP-ABS-UT scheme meets the\nrequirements of unforgeability as well as lower computation cost.
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