[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
PGP Keyserver Synchronization Protocol (corrected)
Sorry, I didn't run the spell checker over the previous post.
PGP Keyserver Synchronization Protocol -- Initial Proposal
William H. Geiger III
01 June 1999
This protocol is designed to allow the synchronization of 2 PGP Keyserver
Databases with the minimal of overhead and network traffic. It will allow
2 servers to detect exactly which keys in their databases are different or
missing and only exchange those keys. This protocol can also be used by
PGP clients to communicate with the servers to compare keys in their local
keyring with those on the server and receive updates to their keys.
The synchronization process involves several steps:
Generation of Hash Tables
Exchange of Hash Tables
Comparison of Hash Tables
Exchange of Keys
In this process one database is initiating the synchronization (client)
while the other is the receiver of a synchronization request (server). To
start the process the client will create a hash table of his database then
he will request a hash table from the server. When the client receives the
server's hash table he will compare it with his own and generate 3 lists:
#1 All Keys that are on the server but not on the client
#2 All Keys that are on the client but not the server
#3 All Keys that are on both client & server but have different hashes
The client will then request from the server all the keys in list #1 & #2
and add those keys to it's database. Once this is done the client will
generate a new hash table for his database and compare it to the hash
table he has from the server. He should now only have 2 lists:
#1 All Keys on the client but not on the server
#2 All Keys on the client & server but have different hashes
The client should then send the server all keys that are in the 2 lists.
Now both servers should be synchronized.
It is common practice among some PGP Keyserver operators to exclude some
keys from their databases (a practice I do not agree with). When doing the
key exchange one may want to take into account the exclusion lists of the
server and not send keys that the client has that matches this list.
FTP of Hash Tables:
A server may wish to periodically create a hash table (once a day) and
store it on his FTP server. This way a client can download the hash table
and do his synchronization without any action on the part of the server. A
more practical approach may be for the servers to maintain a hash table in
"real time" updating it every time keys are added or updated in the
Another approach would be for the servers to create a hash table once a
week and then create daily hash tables that only contain the keys that
have been added/updated for that day.
I am rather flexible on this area and some testing in the field should
provide the best mechanism for when the hash tables should be generate.
A hash table is a sorted index by keyID of all the keys contained in a
PGP Database. The index contains only 2 fields; the 64bit keyID & 128bit
MD5 hash of the key:
It is important that when calculating the hash of a key that it be done
in a specific order as to guarantee that the identical key in two
different databases has the same hash. The following order of operation
for calculating the hash is:
SubKeys Sorted by KeyID
Signatures Sorted by Signing KeyID
UserID's Sorted Alphabetically
PhotoID's & X509 signatures are 2 issues that need to be looked into.
Unfortunately the specs for neither of these packets have been released by
NAI. For right now I recommend that any proprietary packets *not* be used
in the key hash calculations.
William H. Geiger III http://www.openpgp.net
Geiger Consulting Cooking With Warp 4.0
Author of E-Secure - PGP Front End for MR/2 Ice
PGP & MR/2 the only way for secure e-mail.
OS/2 PGP 5.0 at: http://www.openpgp.net/pgp.html
Talk About PGP on IRC EFNet Channel: #pgp Nick: whgiii
Hi Jeff!! :)