Re: [Sks-devel] Re: Delete key from keyserver

[news]

I'm out travelling, so just throwing out some food for thoughts that I can 
elaborate on later. Please excuse spelling errors, as I'm typing on my BB. 

Personally I'n not in favor of hastily adding a deletion method , as it has 
several major implications, but I much appreciate the discussion and agree it 
is good to have it well thought out in case of an 'attack' ( misuse of the 
intent of the sks network ).

The first issue is obviously a situation where a key owned by A is comprimised 
and subsequently revoked. User B, that got hold of a copy of user As private 
key now request a deletion of the key. If the server administrator indulge this 
request, user B now re-upload the non-revoked key or submit this directly to 
counterparties, that won't get the appropriate revocation certificate.

Another issue is on the server level of sks. Addition of a deletion token 
would, by my thoughts, result in a fragmentation of sks servers intu closer 
clusters. You would require a much greater degree of trust between the server 
operators in order to avoid misuse, and so effectively redusing the number of 
peers for each server, but as well limit the servers the peer would be 
'permitted' to recon with in order to be in the cluster. 

Granted this could be mitigated if only 'trusted introducers' (TI)  are able to 
add deletion tokens ( but as long as the protocol is open, this, itself, would 
require a lot of thought on implementation. E.g by adding an element to the key 
to be deleted that is signed by the TI. 

Kristian Fiskerstrand

------Original Message------
From: Yaron Minsky
Sender: address@hidden
To: Jeff Johnson
Cc: address@hidden
Cc: Sebastien
Cc: Ari Trachtenberg
ReplyTo: address@hidden
Subject: Re: [Sks-devel] Re: Delete key from keyserver
Sent: 8 Sep 2010 05:27

I'm not sure that inserting the new tag in the offending key is really the 
simplest way of encoding this. Here's a short description of the algorithm I 
have in mind.  The basic thing to understand about SKS is that it works by 
agreeing on sets of values.  When node A and B (with sets S_A and S_A) 
communicate, they figure out the hash-values that each is missing from the 
other, i.e., S_A - S_B and S_B - S_A.  Then, based on those hash values, A and 
B request the missing data. Currently, the set elements are keys.  To support 
deletion, you would want to extend the values so they logically were a union 
type: type set_element = | Key of Key.t                    | Deletion of Hash.t 
where Key.t is a PGP key, and Hash.t is the type of the hash of a set_element. 
The idea is that when a key-server adds a Deletion to its set of keys, it 
actually deletes the corresponding element from its data set.  Now, consider 
what happens if A has a deletion for a value that B still has.  A will discover 
it's missing the key in question, and B will discover it's missing the 
deletion.  Each will request the missing element from the other. A's request 
will succeed, but will have no effect, since A will know to delete the key.  
B's request will succeed, and it will as a result delete the key in question 
from its database. If we want to delete the deletions, we can extend 
set_element with one more variant: type set_element = | Key of Key.t            
        | Deletion of Time.t * Hash.t                    | Deletions_stable of 
Time.t We've added a time to the Deletion, which is the time the deletion was 
added to the system.  The Deletions_stable element is meant to indicate that 
all deletions sent before the specified time are assumed to be stable, and can 
thus be discarded (and older Deletions_stable elements can also be discarded).  
Thus, if someone periodically sends out a Deletions_stable after a decent time 
period, then this will clean out old deletions from the system. Presumably, the 
Deletion and Deletions_stable entries would need to be signed by some trusted 
key before they would be accepted by a given keyserver.  But that goes to the 
policy question... y On Tue, Sep 7, 2010 at 10:28 PM, Jeff Johnson 
<address@hidden> wrote: On Sep 7, 2010, at 9:50 PM, Yaron Minsky wrote: > I 
think that a basic form of deletion is pretty easy, and requires no real 
research  The algorithm is simple.  You simply add a new kind of pseudo-key to 
be gossiped around: a deletion token.  In the simplest version, the deletion 
token never expires; it's a permanent addition to the database.  But the effect 
of adding the deletion token is that the thing it wants to delete is 
effectively removed.  With a small amount of extra cleverness, one can allow 
the deletion token to be removed eventually as well.  But given the small 
number of deletions that appear to be necessary, it hardly seems urgent. > 
Thanks. When I hear "pseudo-key" and "deletion token", I also hear a form of 
"white out". Since RFC-2440/4880 already has well understood attributes of 
revocation and expiry, then I would hope that a "pseudo-key" could actually be 
grafted on as another attribute tag on an existing revoked/expired pubkey with 
the additional meaning        This pubkey is now a "pseudo-key deletion token" 
and should be ignored while gossiping. If all the key packets except        the 
pubkey        the revocation        the additional attribute that indicates 
never distribute are stripped out (specifically the userid and all 
certification signatures), that might be sufficient even for lawyers -- is it 
possible to "own" 1 or more MPI's  if there are no identifying marks to 
indicate the owner? I'll leave that to others with the usual IANAL disclaimer. 
So my next question would be:        Is it feasible to craft up a special 
"pseudo key" as above that -- when fed manually to        each SKS server  -- 
would replace, not augment, the existing offending pubkey and        NEVER be 
gossiped. I add "manually" solely to uncouple the token from its distribution. 
What I don't know is   1) Can the deletion be handled as an attribute?   2) How 
should that attribute be represented as a RFC 2440/4880 tag? The next step 
would be to relax the "fed manually" so that the pseudo-key could be gossiped, 
thereby replacing every occurrence of the offending pubkey with the "pseudo key 
deletion token". Does that sound like the basic framework that would be needed? 
73 de Jeff > There is a policy question: who gets to add a deletion token to 
the system?  The owner of the key to be deleted?  Or perhaps there are a set of 
trusted administrators shared by the whole network who can ask for deletions? > 
> And, of course, there's the question of who is going to do the work.  I don't 
have the time to devote to SKS at this point, so if this feature is to be 
added, someone else needs to do it. > > y > 
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