And then, what do you mean by “steal?” Because steal is also defined as “sneak.” It’s no the same as walking boldly into the 7-11 and “liberating” a Slurpee. So by opposite do you mean, “to procure with stealth” or do you mean simply “to unrightfully appropriate?”
Clearly there is work to do.
Aver (from Latin ad- + verus true) is about as close as it gets:
1 a : to verify or prove to be true in pleading a cause
Antimendicate?
There are quite a few multi-part verbs in English. Why shouldn’t “utter the truth” be among those?
Beat me to it, damn you. 
Truthify.
I second this one. The word “aver” appears in legal affidavits all the time, as in “The affiant hereby avers that…” In such a case, aver has the meaning above, which basically means “tells the truth”.
Veredict. Okay, I made it up. But so what? It comes from the same combination of Latin roots as “verdict” – in fact, it seems to be an alternate spelling of the word in some places. So if one accepts the word “contradict” as a template (against + to speak), than one may, with little fear of being misinterpreted, speak of someone veredicting…speaking truly.