  Recent trend towards cloud computing paradigm, smart devices and 4G wireless
technologies has enabled seamless data sharing among users. Cloud computing
environment is distributed and untrusted, hence data owners have to encrypt
their data to enforce data confidentiality. The data confidentiality in a
distributed environment can be achieved by using attribute-based encryption
technique. Decentralized attribute-based encryption technique is a variant of
multiple authority based attribute-based encryption whereby any attribute
authority can independently join and leave the system without collaborating
with the existing attribute authorities. In this paper, we propose a
privacy-preserving decentralized key-policy attribute-based encryption scheme.
The scheme preserves the user privacy when users interact with multiple
authorities to obtain decryption keys while mitigating the well-known user
collusion security vulnerability. We showed that our scheme relies on
decisional bilinear Diffie-Hellman standard complexity assumption in contrast
to the previous nonstandard complexity assumptions such as $q-$decisional
Diffie-Hellman inversion.
