I had a request to post a guide on how to get to level 34 since there was some confusion.

You do not need any keys or anything like that.

To get to 34, all of your armor has to have 42 light each. You can either acquire armor with 42 light, or ascend existing legendary or exotic armor.

Acquire: Amor you buy from the Prison of Elders vendor in the reef will have 42 light. It can be purchased with an armor core, which can be obtained by completing Prison of Elders on either level 32 or 35. Trials of Osiris armor also has 42 light, and can be purchased by winning the required (4) number of matches.

Ascend: You can easily ascend exotics using exotic shards. Ascending legendaries requires etheric light. You can obtain etheric light in Prison of Elders 34/35, Trials of Osiris, Nightfall, or Iron Banner.

Path to 34 for one character: Ascend an exotic. Run the Prison of Elders lvl 32, and use the armor core to purchase armor. You're now 33. Complete Prison of Elders on level 34 to get one etheric light, and ascend your boots. Tomorrow, win 4 times at trials of Osiris and buy the chest piece. Alternatively, if you got etheric light from the nightfall or from other characters, you can just ascend the required armor pieces and do it that way.