[ntp:hackers] Information needed in providing server's public key to client in secured NTPv4

Chandramohan, BA IN BLR SISL Chandramohan.ba at siemens.com
Mon Aug 3 09:14:49 UTC 2009

Hal Murray,

Thanks for the information.

We can use PGP & GNUPG only to generate public keys and certificates.  

We can send the public keys of the server by 'out of band' means.
But I think there is some means in NTP protocol through which we can send the server's public key for encryption/decryption of cookies and signature.

There are few parameter exchanges and one of them is 'Association Message' (ASSOC) which happens before cookie request/response. I guess that exchange of server's public key is done here.

In association message (ASSOC), client sends its status word to the server and server sends its status word as response.
Host status word has Host Key and Sign Key.
Host key contains the public/private key pair to encrypt/decrypt cookies and Sign key contains the public/private key pair encrypt/decrypt signatures.
You can the check the link "http://tools.ietf.org/html/draft-ietf-ntp-autokey-06" for more information.

Can you let me know how this exchange happens and what are the members and their data types of the host status word?

Is the public key of the server exchanged through this parameter exchange request/response (ASSOC message) or this has to be done through 'out-of-band' method through e-mail or registered mail?

With best regards,

-----Original Message-----
From: hackers-bounces+chandramohan.ba=siemens.com at lists.ntp.org [mailto:hackers-bounces+chandramohan.ba=siemens.com at lists.ntp.org] On Behalf Of Hal Murray
Sent: Monday, August 03, 2009 10:30 AM
To: Chandramohan, BA IN BLR SISL
Cc: hackers at lists.ntp.org
Subject: Re: [ntp:hackers] Information needed in providing server's public key to client in secured NTPv4

Chandramohan.ba at siemens.com said:
> Client sends its public key and signature in COOKIE request. Server
> verifies the client's signature, sends COOKIE and its signature to the
> client in COOKIE response Now client has to verify server's signature
> and for this it needs server's public key. How is this information
> (server's public key) provided to the client? 

The magic word is "out of band".  How you get it is outside the NTP protocol.

Email is probably good enough.  If somebody was going to slip you the wrong 
key, they would have to intercept the mail from your clock source, substitute 
the bogus key, make it work long enough to fool you, and then use it before 
you noticed a problem.

You might find it on a web site.

If you don't trust that, you can use registered (postal) mail.  (That assumes 
the people providing the time and key will go through that effort.)  Or send 
a courier to their office...

You could use PGP or GnuPG, but that's the same problem all over again.

These are my opinions, not necessarily my employer's.  I hate spam.

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