Table 2 the notations used in performance comparison

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TABLE 2. The notations used in performance comparison. VOLUME 8, 2020 176745
L. Li et al. : Efficient Attribute-Based Encryption Outsourcing Scheme With User and Attribute Revocation TABLE 3. Comparison of functions. Phase 2. A repeatedly the process in Phase 1, but the restriction is that the two messages m 0 and m 1 cannot be challenged. Guess. A returns a guess bit θ 0 ∈ { 0 , 1 } . B returns h = 0 indicating that T = e ( g , g ) abc on the condition that θ 0 = θ ; otherwise, B returns h = 1 indicating that T is a random element in group G T . If T = e ( g , g ) abc , then A can break the security game with an advantage ξ , and the B ’s advantage Adv ( B ) in solving the DBDH problem is 1 / 2 + ξ ; otherwise. Adv ( B ) = 1 / 2. Hence, the advantage of B in breaking the security game outlined above is defined as Adv ( B ) = 1 / 2(1 / 2 + ξ + 1 / 2) - 1 / 2 = ξ/ 2 VI. PERFORMANCE ANALYSIS In this section, we analyze and compare the efficiency of the proposed scheme with other schemes in theoretical and experimental aspects. A. THEORETICAL ANALYSIS We compare the performance of the proposed scheme and other schemes in the following 4-parameters: 1) function comparison, 2) storage overhead, 3) computation overhead, and 4) communication overhead. The notations used in performance comparison are repre- sented in Table 2. 1) FUNCTION COMPARISON Table 3 compares the functions of the proposed scheme with existing schemes. It shows that our scheme has richer func- tions than other schemes and is more suitable for the IoT than previous related schemes. 2) STORAGE OVERHEAD We mainly consider applying our scheme to IoT devices with limited resources, so we focus on its storage performance on the end user side as shown in Table 4. The storage overhead of a data owner mainly depends on public keys generated by different AAs which are used to encrypt data. Our scheme supports outsourcing encryption, and public keys are stored by FNs, so our storage overhead is much lower than most other schemes. The storage overhead of a data user mainly depends on his secret key. Our scheme stores the attribute keys of data users in FNs for outsourcing decryption, so the TABLE 4. Comparison of storage overhead. storage cost of a data user is less than that in [12]. However, due to the complexity of user identity key construction, it is higher than other remaining schemes. 3) COMPUTATION OVERHEAD Table 5 compares the computation overhead of end users, including encryption of the data owner and decryption of the data user. We mainly consider several time-consuming operations like bilinear pairing operation and exponential operation. In the comparison, our scheme costs less compu- tational overhead than other schemes, because most of the encryption and decryption operations are outsourced to FNs in our scheme. TABLE 5. Comparison of computation overhead.

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