Were you planning to tell him the passphrase? Anyway, you're not going to be able to distinguish between 'we figured it out and are pretending not to' and 'we decided to let it rest', so you're not going to have the security you want either way.

It might be less obvious than you think. We did know you had spies and a research team.

Both of which I have strictly more information about than you do. 

True. If you want to gamble on finding out and hiding the fact that you did, I can't stop you.

I don't want to do that. I'll discuss it with my people and I expect we'll decide to figure it out and then help and I will tell you both of our decision and when we figure it out. I just feel obliged to point out that if you're treating us as hostile you're doing a bad job of it.

You also said there was a second secret, you could very plausibly have led with the one we'll be able to derive in order to have a justification for the question that didn't call a lot of attention to the much-more-important second secret.

We don't think you're hostile. We don't expect you to become hostile and are gambling on that probability.

So, absent the problem of me being tricky with oaths, is there even anything that would reassure you. Even complete and total assurance that I am currently acting in the best interests of your host as far as I can and don't expect anything to change that doesn't actually protect against what you seem to be afraid of...

Not that we could think of. It might just be an impossible question.

Or maybe complete certainty that no one will ever have interests counter to yours is the wrong standard to be using for decisionmaking.

Depends on the decision, doesn't it. But yes, we're less paranoid than that or we'd be cutting you out completely.

I don't think that'd be the right call even under maximum paranoia; you still don't know how we're spying on you. 

Trying to, then.
The unknown spying method sounds like a reason to be more paranoid, but why would it suggest telling you more if we were?

If the outcome should you ignore us entirely is 'we don't get any information', that's a reason to try it. If the outcome is 'we get an unclear but significant share of the information anyway, and can't run ideas by you to check if they're safe or worthwhile, and have no incentives to not annoy you...'

And if we don't mind incentivizing you to spy in the first place.

But we're not actually trying that; it can stay safely hypothetical.

I can stop the spying. It sounds like you mostly don't want us to know these things because you don't trust us not to use them against you, and I trust myself not to use them against you, so that reason is not a reason to stop spying. But I can, if you have a better reason than that.

It's that, plus the fact that if we're the only ones who can replicate this then we don't have to be watching our backs nearly as much. Even once you're more powerful than we are.

That's a good argument for telling you I've stopped spying on you.

With the obvious side effect if you do say that. If it's undetectable enough, probably every reason comes with the same distinction.

Fundamentally, if you don't trust me you're not going to be able to let your guard down regardless of what I'm actually doing.

Probably not. Just thought I had to check in case there was an astoundingly clever way around that.

If there were anything costless I'd do it already. There are costly ways to verify current sincerity of intentions and the absence of any clever games or oaths or commitments that would affect intentions. If that's not sufficient, then the only way is an oath over future actions and nothing you've mentioned would make that worth it. 

Yeah, that'd be extreme.

Oh well. Good skill and luck as applicable, with the running a war.

Likewise. Sigh. I'd have told you what I was going to do if I had anticipated you'd react by refusing to accept any conceivable proof we weren't about to attack you.

It's–  no, he already knows the precise degree of exaggeration there.

I wish there'd been some easy solution.
Anything else we need to talk about?

No. Take care.