Scaling down the marks?

For the other modules I gave in the past, the problem of exam marking is to give out as much marks as possible. This time however, the cryptography module has an average that is so so high and we almost have to scale it down. Although, at the end, it was not done. I really don't know why the marks are so high. (Can I just say my teaching is very good?) I don't think the exam paper is too simple. If the same paper is given to the batch of students last year, I'm pretty sure the situation would be entirely different...