In SCRUM, where detailed requirements are captured?

I always hear that a user story should be very short and clear, so it can be write on a note etc. Like "As a user, I want to be able to enter, modify and delete People in the directory".

But for testing, we need to know:

• -what are the fields, what are boundaries and ranges (int16-32?)
  
  -what are the validation messages
  
  -length of strings etc.

How this is solved in SCRUM?