[jihoon796]

If you must do whiteboard interviews, here's a technique I've used with great effect:

Have someone else pick a coding problem (that you as the interviewer don't know beforehand), and work on it from scratch together with the candidate.

Being upfront with the candidate that you don't know the answer yourself puts the candidate at ease, and you'll be able to better judge the candidate's soft skills (communication, critical thinking, empathy in case I don't understand the problem).

[pdxandi]

I like this idea. Personally, I struggle with knowing that the interviewer knows the answer. My wife's in medicine and she and her colleagues call this process "Guess what I'm thinking?" I prefer to have dialog and come to a conclusion together, and I feel it gets what you want out of an interview: how does the candidate think, how deep is their understanding of the technology, how do they communicate, and would you enjoy working with them.