Open-source PAL

Steven M. Bellovin smb at
Sun Dec 2 20:24:32 EST 2007

On Thu, 29 Nov 2007 16:05:00 -0500
"Tim Dierks" <tim at> wrote:

> A random thought that's been kicking around in my head: if someone
> were looking for a project, an open-source permissive action link (
> is a good link,
> thank you Mr. Bellovin) seems like it might be a great public
> resource: I suspect it's something that some nuclear states could use
> some education on, but even if the US is willing to share technology,
> the recipient may not really trust the source.
> As such, an open-source PAL technology might substantially improve
> global safety.
I don't think it would be fruitful.  Have a look at page 2 of -- it notdes
that "The system hinges on what is essentially a switch in the firing
circuit that requires the would-be user to enter a numeric code that
starts a timer for the weapon?s arming and detonation."  I don't think
that that's quite correct -- it permits arming; PALs are not in the
firing circuit, I believe -- but this section is more interesting:
"Delicate design details involve how to bury the link deep inside a
weapon to keep terrorists or enemies from disabling the safeguard."
In other words, it's easy to have a circuit that keeps the bomb from
arming; the hard part is doing so with high assurance against attacks,
and that's very design-dependent.

		--Steve Bellovin,

The Cryptography Mailing List
Unsubscribe by sending "unsubscribe cryptography" to majordomo at

More information about the cryptography mailing list