Maybe this meets your needs:

  http://securestorage.sourceforge.net/

Yushu Yao wrote:
> Well, please let me rephrase my question.
> 
> I need an access control like AFS, where a user can encrypt a file, put it
> on a public place (eg, http), and only the users/groups he specifies can
> decrpyt it. (without directly sending his public key to the receivers).
> 
> I guess some trusted party (Authentication Server) needs to exist in the
> middle to handle this, and this party holds the identity of all the users
> (e.g. the CA who give all the users certificates).
> 
> One possible procedure: when B sees a file online, it will ask the
> Authentication Server for the key to decrypt this file, the Authentication
> Server will see if A has let B to see this file, if yes, send B the key, if
> no deny it.
> 
> Is there anything similar to this? Or is this idea totally idiot and this
> should be handled in some other way?
> 
> Thanks a lot!
> 
> -Yushu
> 
> 
> 
> 
> On Mon, Sep 21, 2009 at 8:03 PM, Yushu Yao <[email protected]> wrote:
> 
>> Hi Experts,
>>
>> Just a general question about encryption.
>>
>> Assuming a CA has issued 2 users (A and B) valid certificates.
>>
>> Can A encrypts a file and specifies that only B can read it? If yes, how
>> could this be done? If no, any alternate way to do this?
>>
>> Also, what if A encrypts a file and want a group of users (have valid
>> certificates from the same CA) to be able to read it?
>>
>> Thanks a lot!
>>
>> -Yushu
>>
>>
>>
>>
>>
>> +-------------------------------------------------+
>>  | Yushu Yao
>> | Ph:1-510-486-4690
>> |
>> | Lawrence Berkeley National Lab
>> | Mailstop 50B-6222
>> | 1 Cyclotron Road
>> | Berkeley CA 94720-8147 - USA
>> +-------------------------------------------------+

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