Secret Alliance vs. Secret Negotiation

Just a quick question.
Are we allowed to communicate secretly with other players in the game? By this I mean, could I PROPOSE an alliance with another player via PM, and then, if that other player accepts, announce it on game chat if the agreement is reached?
Are we allowed to communicate secretly with other players in the game? By this I mean, could I PROPOSE an alliance with another player via PM, and then, if that other player accepts, announce it on game chat if the agreement is reached?