Bismillah

Assalamu alaikum,

Key that is opening something, many Scholars have interpreted this dream as the Du`a has been accepted.

If however, the keys was just in the hands not opening anything, sholars have interpreted this 1) To gain wealth 2) To have respect 3) To have authority 4) To gain knowledge. It is mentioned in Bukhari, Book of interpretations of dreams in the chapter of "Keys in the Hand."

Narrated Abu Huraira:

The Prophet said, "I have been given the keys of eloquent speech and given victory with awe (cast into the hearts of the enemy), and while I was sleeping last night, the keys of the treasures of the earth were brought to me till they were put in my hand." Abu Huraira added: Allah's Apostle left (this world) and now you people are carrying those treasures from place to place.

*Bukhari, Volume 9, Book 87, Number 127*

And ALLAH Taala Knows Best.