Question regarding group management of documents

[Anne & Lynn Wheeler]

I was at a presentation last week of a company that is doing something like 
this .... including cross-domain authentication. it looked very much like 
kerberos architecture but using packets with SAML formated data (as tickets).

they listed several financial institutions as well as some gov. operations
http://www.sigaba.com/

random saml related references ....
http://www.garlic.com/~lynn/aadsm11.htm#19 IBM alternative to PKI?
http://www.garlic.com/~lynn/aadsm11.htm#30 Proposal: A replacement for 3D 
Secure
http://www.garlic.com/~lynn/aadsm12.htm#5 NEWS: 3D-Secure and Passport
http://www.garlic.com/~lynn/aadsm12.htm#6 NEWS: 3D-Secure and Passport
http://www.garlic.com/~lynn/aadsm12.htm#58 Time to ID Identity-Theft Solutions
http://www.garlic.com/~lynn/aadsm5.htm#spki4 Simple PKI
http://www.garlic.com/~lynn/aepay10.htm#57 SAML Just The Start For Web 
Services Security
http://www.garlic.com/~lynn/aepay10.htm#76 Invisible Ink, E-signatures slow 
to broadly catch on (addenda)
http://www.garlic.com/~lynn/aepay11.htm#1 Sun releases Liberty-enabled software


At 09:38 AM 1/16/2003 +0100, Birger Toedtmann wrote:

>Hi,
>
>can anyone pinpoint me to some papers on this - the Net did not show
>up anything useful (and I hope it's not my lacking competence in using
>Google).
>
>
>I'd like to use a server to share documents between users.  The users
>are grouped, i.e. a user of group A should not be able to read the
>docs of group B (if not a member of it).  There are conceptually two
>possible ways to design this:
>
>  * use an "out-band-process" (an operating system watching over
>    file permissions, a web service verifying user credentials etc.)
>
>  * use in-band crypto on the document itself, i.e. the "permissions"
>    are inherently tied to the bits it consists of
>
>I wanted to use the latter with a critical constraint: ease of deploy-
>ment (at least in a sense) which basically means that we don't want
>to write a new client but use freely available ones.  So my first
>guess was to PGP-encrypt the files on the server using the public
>keys of the group-members.  The server obviously should not have the
>secret keys of them.  I further assume that (a) a member-no-more takes
>his secret key with him and (b) the server may be hacked but the hacker
>should not be able to read the documents (but may corrupt/delete them).
>
>So far, so good.  Now a user leaves a group.  As the server is not
>able to decrypt files and we don't want someone to decrypt 1000 files
>of a group and re-encrypt them again with the members left, it would
>be possible to just encrypt the already-crypted file again with the
>"new" group of the remaining members (adding sort of a second armor).
>Despite this being quite stressing for users if a file has some-20
>armors, I did not come up with an idea for adding *new* members to a
>group....
>
>
>Well, maybe I'm already on the wrong track for this issue, so I
>appreciate any suggestions or hints to sites/papers discussing these
>problems.
>
>
>Regards,
>
>Birger Tödtmann
>
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--
Anne & Lynn Wheeler      lynn at garlic.com,  http://www.garlic.com/~lynn/ 


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