PDF | Outsourced decryption ABE system largely reduces the computation cost for users who intend to access the encrypted files stored in. Request PDF on ResearchGate | Attribute-Based Encryption With Verifiable Outsourced Decryption | Attribute-based encryption (ABE) is a public-key-based. , IRJET | Impact Factor value: | ISO Certified Journal | Page Attribute-Based Encryption with Verifiable Outsourced Decryption.

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If such a tuple exists, it returns as the transformation key. Theorem 6 is correct from the two lemmas below.

### Verifiable Outsourced Decryption of Attribute-Based Encryption with Constant Ciphertext Length

If wins the above game, then can obtain where and are obtained by. It sends to the adversary and keeps secret. An encryptor randomly selects. Note that, in our scheme, a ciphertext consists of three parts: Note that, with overwhelming probability, has multiplicative inverse.

It outputs public parameter and master secret key.

He chooses and computes the transformation key aswhere and. In their scheme, a user uses proxy reencryption method [ 1314 ] to attribute-basedd a transformation key and sends the transformation key and ABE ciphertext to the CSP. Thus, we come to a conclusion that the advantage for an adversary in is negligible. This algorithm takes veririable,and as input. Therefore, our scheme is very efficient. Otherwise, selects random exponents. Given ciphertext and transformation keythe CSP computes as follows: Data owner encrypts message into ciphertext and uploads it to the storage in cloud.

The security property about ABE with outsourcing decryption ensures that the malicious cloud server cannot obtain anything with respect to the encrypted message; nonetheless, the scheme does not ensure the validity of the transformation done by the CSP. Assume that the scheme in [ 33 ] is outslurced CPA-secure. Note that,is assumed. Bilinear Pairing Definition 1 bilinear map.

Therefore, if is able to distinguish and at nonnegligible advantage, we are able to find veriiable algorithm that attacks the scheme [ 33 ] in selective CPA security model at nonnegligible advantage. To deal with above problem, Li et al. Without loss of generality, we suppose that the adversary does not launch transformation key query for attribute set rncryption, if a private key query about the same attribute set has been issued.

This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Table atteibute-based illustrates that the size of private key, ciphertext, and transform key in our scheme is constant. We prove security and verifiability of our scheme in Section 4. The first two elements are ciphertexts for message and random messagerespectively, utilizing the encryption algorithm [ 33 ].

The size of ciphertext and the number of expensive pairing operations are constant, which do not grow with the complexity of the access structure. Namely, and decryption queries are replied to as phase 1; if the response is either orthen returns. We have that the assumption holds with overwhelming probability: Preliminaries We introduce some basic knowledge about bilinear groups, security assumption, access structure, and CP-ABE which our scheme relies on.

It allows users to use flexible access control to access files stored in the cloud server with encrypted form. In order to solve this problem, Goyal et al.

Table 3 illustrates that only our scheme satisfies all properties. We organized the rest of the paper as follows.

### HKU Scholars Hub: Offline/online attribute-based encryption with verifiable outsourced decryption

As the amount of decryprion files stored in cloud is becoming very huge, searchable encryption scheme over encrypted cloud data is a very challenging issue. The game proceeds as follows. An outsourcing decryption CP-ABE scheme is selective security if we add an initialization phase prior to setup algorithm in above game, where the adversary gives the challenger access structure. The elliptic curve parameter we choose is type-A, and the order of group is bits. A user checks whether the transformed ciphertext or or ; if the equations do vdrifiable hold, he outputs.

It is described by the seven algorithms as follows.

## Security and Communication Networks

The master secret key is. In order to evaluate the efficiency for our scheme, we implement our scheme with java pairing-based cryptography JPBC library [ encryptioj ], a port for the pairing-based cryptography PBC library in C [ 37 ].

In this article, we present a novel verifiable outsourced CP-ABE scheme with constant ciphertext length to save the communication cost.

Encryptioon algorithm takes the security parameter and attribute universe as input. With the cloud service being more and more popular in modern society, ABE technology has become a promising orientation. We suppose that tuple is included in table.

Then our new scheme is selectively CPA-secure. The notation denotes that an attribute set satisfies an access structure ; that is to say.