Attribute Based Encryption

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C#

ASP.NET

pls any one help me....

i want to create a module in my project based on attribute based encryption asp.net c#.

its based on social communication for health department...

imagine there are too many users having a account in my project and these users are interconnected like one user send friend request to any one that request was accepted by the particular user they are friends. if one user having 10 friends and the user having one important file that 10 friends want to download that file. in this section how can i encrypt and store the file using attribute based encryption and how can i produce different keys to my friends they do decrypt and download it...

i need how to develop this module..
i have no knowledge in attribute based encryption...

pls help me how can i do this.....

need related link...
show me your ideas....