My problem is the following:
I have an organization with many members. When someone from the outside communicates with this organization, I want any member to be able to decrypt the communication.
On solution I found would be to use CP-ABE: the organization has a master key and a public key related to it. The owner(s) of the organization can then issue secret keys for all members with a dummy policy that always evaluates to true. That way, an outsider won't have to know anything about the internal structure of the organization or its members; he will just have to encrypt using the organization's public key and any on its members will automatically be able to decrypt using his secret key.
The thing is that I really don't need all the attribute policy part of the CP-ABE so this seems overkill to me. I was wondering if there were any key derivation schemes that would allow me to do so, but I couldn't find any.
I remind my constraints:
- the encryption should be done with a single public key for the whole organization
- each member should have a different derived secret key
If there is such a scheme, how can we enforce key revocation ?