.NET Security

If there is a better group for this, please tell me. From time to time, ex-students contact me with questions that prove the old adage "Those who cannot do, teach". I'm always pleased to see how quickly they progress after graduating. Here's a case in point :-) ...

What is 3-des' keylength?  and how is 3-des implemented with regards to key usage? Documentation says "standard" length, but that doesn't tell me keylength. I understand that some implementations can be 56, 112, or 168 bits, ...