Table 3.

Comparison of security requirements of this proposed scheme and the existing CP-ABE.

	Hahn Scheme [12]	Jiang Scheme [12]	Yu Scheme [22]	Qi Li Scheme [5]	Premkamal Scheme [17]	Jiguo Li Scheme [18]	Proposed Scheme
Collusion/ masquerade attack	Safe
Data Storage space	Efficient	Inefficient				Efficient
Ciphertext length	Constant size	Proportional to the number of attributes				Constant size
User privacy	Infringement impossible	Infringement Possible (Trusted servers manage user information through identity tables)			Infringement impossible
Tracing the first user to distribute the key	Untraceable	Traceable via identity table	Traceable with user signatures stored in identity tables	Traceable via identity table	Untraceable		TA and AA work together to track who was issued the first key
Verifying the integrity of the data owner’s message	Not considered			Message verification with VK, which can verify ciphertext		Verify by inserting MAC authentication code in ciphertext	Verify by inserting the message hash value in the ciphertext
Outsourcing operation support	Supported	Not supported		Supported