Week 9, summary 
---------------
Quantum cryptography.

1.   Impossibility of quantum bit commitment.

2.   Quantum biased coin flipping. 
 
2.   Quantum key distribution.  
      I will present a beautiful proof by Shor and Preskill
      that this protocol is secure with no computational assumptions. 
      The proof uses quantum error correcting codes. 
 

   The protocols for biased coin flipping and for secure 
   key distribution are secure with NO computational assumptions 
   on the ability of the evesdropper- the evesdropper can be mighty 
   powerful. (such unconditional security guaranties is unique 
   to the quantum world, provably classical protocols cannot provide 
   such security. )