> The rest of it is all about asking the associated companies, politely, to cooperate.

What keeps this cooperation secret? It would only take one weak link at any one of those companies to reveal -- accidentally or otherwise -- that they were coerced into providing their signing keys. As soon as that got out, speculation runs amok: Are all products from said company compromised? This would be ruinous to a company, so no one in charge would agree to that without something significant -- which would be even harder to hide from the public -- in return. Then, who asked for the key and why? Could that be traced back to the (presumably) agency in question? That weak link was weak once, there's nothing to assume that he/she won't be weak again, etc., etc.