[ntp:hackers] UDel security

Steve Kostecke kostecke at ntp.isc.org
Thu May 12 13:44:47 PDT 2005

Note: Lightly reformatted and slightly reordered to allow in-line

"David L. Mills" said:

>"Danny Mayer" said:
>>"David L. Mills" said:
>>>I am asking the ISC to regularize the Autokey group key provision
>>>via the web. Can we set up a scheme that allows registration and
>>>retrieval of a group key for designated machines?
>>Are you talking about the autokey key distribution scheme that Steve
>>set up?
>At the moment, I can't find the magic secure web page that serves as a
>way to get the group key wrapped in a shell script that installs the
>key and links.

My IFF key request page is at https://ntp.isc.org/crypto.php

That key request page currently only provides users with a way of
viewing or downloading their key. There is no shell-script wrapper,

>>Or is this something else? What keys would be distributed and
>>for what machines?
>Recent experience at USNO and NIST strongly suggests some form of
>mandatory access control is necessary for at least some public servers.
>Case in point is at USNO, where the operators want to screen out all
>except military customers. Autokey and notrust would seem the natural

Group key files with a group password are not a decent means of access
control because there is nothing to prevent the free exchange of the
group key. As I understand it, NTP Authentication is only intended to
authenticate the server's packets to it's clients. The way to control
access is with ntpd restrictions or at the router/firewall.

>What I would like to see at ISC is a secure web page which does this
>where the user supplies the server name and password to encrypt the

Since the key request page is only accessible via SSL I don't understand
why the key would need another layer of encryption in transit.

There needs to be a way to authenticate the users before giving out
keys. Otherwise anyone could request a key for any server. And we're
back to the problem of uncontrolled access.

>The group key could be supplied at the time the public list is updated.
>I would assume some way would be required to upload the group key. Is
>this possible?

This sounds like you would like ISC to be the group key distribution
point for other organizations. This is really not the right approach for
a number of reasons. Although the bandwidth requirement may not be high,
there will almost certainly be liability issues (e.g. who is responsible
if the USNO group key is released to the wrong party?). And there is the
group password issue.

There are two files, in addition to the host parameters, used in the
IFF identity scheme: the server parameters (IFFpar) and the client key
(IFFkey). The IFFkey file is encrypted with the client's password when
it is exported from the IFFpar file (either by the server or a trusted
third party). Yes, it is possible to use the IFFpar file on all of the
members of an NTP Trust Group. But, in practice, you really don't want
to do this.

If you use an IFFpar file as a shared group key, every member of the
Trust Group must use the same crypto password (e.g. a group password).
This is not necessarily a show-stopper for systems which only belong to
one NTP Trust Group, although I'm sure that most time server operators
would not want to reveal their crypto password to anyone else. You could
export a group IFFkey and encrypt it it with a group (client) password.
This method avoids revealing the server's crypto password, but you still
are using a group password.

Group passwords are a significant issue when systems are members of more
than one Trust Group. Since a system only has one crypto password, all
of the group keys would need to be encrypted with that same password.
The end result would be many groups using the same group password so
that systems may belong to multiple Trust Groups unless there is a way
for clients to use unique crypto passwords.

Unless there is a way of adding a client password to a group key
(IFFkey) subsequent to the export process, we would need to have a copy
of the server key file (IFFpar) _and_ know the server's crypto password
so that we can export IFFkey files on the fly. The server's RSA-MD5cert
and RSAkey files are not needed during the export process.

Steve Kostecke <kostecke at ntp.isc.org>
NTP Public Services Project http://ntp.isc.org/
Public Key at http://ntp.isc.org/Users/SteveKostecke

More information about the hackers mailing list