Privacy Protection of Task in Crowdsourcing: Policy-Hiding and Attribute Updating Attribute-Based Access Control Based on Blockchain

Table 1

Notation description.

Notations	Descriptions
	Two cyclic multiplicative groups
	The attribute universe
	An attribute set
	An access policy
	An attribute
	A security parameter
	A public key registered in blockchain
	A private key registered in blockchain
	A public key in CP-ABE
	A secret key in CP-ABE
	A master secret key in CP-ABE
	Task information
	A fully homomorphic cryptosystem
	A collision-free hash function
	A CP-ABE ciphertext
	A transaction on the blockchain