Prove is the infinitive. Proved is the past simple. Since it's an ed ending to follow the pattern one would suppose proved to be the past participle and this is true in standard British English.
Proven comes along and sounds similar to a typical irregular verb ending as in eaten or spoken.
The whole thing becomes confused. And this is where research needs to be done. Proven is used as the adjective. Additionally in American English it has been adopted as a past participle increasingly, though not completely. At times it is used, at times proved.
To clear it up. If you want to be rigorous, go with proved as both past simple and past participle, and use proven as the adjective. As in "a proven theory".
Another example with a similar dual past participle is rive, (infinitive) with the option of either rived or riven, which means split apart or broken apart.