title: Questions about the NaCL crypto library
body: <p>I was looking for libraries to implement an encryption system and was interested in using the NaCl: Networking and Cryptography library specifically the <a href="http://nacl.cr.yp.to/box.html" rel="nofollow">box function</a>. Obviously, it uses symmetric encryption XSalsa20, Curve25519 for public-private cryptography and Poly1305 for authentication as the primitives for it.</p>
  
  <p>However, the documentation looks to be insufficient in the way the they've been used. For example, it mentions that to compute the key it uses the sender's private key and the receiver's public key to compute the secret key. But it doesn't explain how. Can anyone shed any light on it?</p>
  
  <p>If I were to use the same public and private key, I wouldn't the same key to be generated on the next attempt and it would be disastrous. Does anyone know of the explanation behind it or hook me up with some more documentation on how the functions work rather than how the functions can be used?</p>