  The recent application of the principles of quantum mechanics to cryptography
has led to a remarkable new dimension in secret communication. As a result of
these new developments, it is now possible to construct cryptographic
communication systems which detect unauthorized eavesdropping should it occur,
and which give a guarantee of no eavesdropping should it not occur.
  CONTENTS P3. Cryptographic systems before quantum cryptography P7. Preamble
to quantum cryptography P10. The BB84 quantum cryptographic protocol without
noise P16. The BB84 quantum cryptographic protocol with noise P19..The B92
quantum cryptographic protocol P21. EPR quantum cryptographic protocols P25.
Other protocols P25. Eavesdropping stategies and counter measures P26.
Conclusion P29. Appendix A. The no cloning theorem P30. Appendix B. Proof that
an undetectable eavesdropper can obtain no information from the B92 protocol
P31. Appendix C. Part of a Rosetta stone for quantum mechanics P44. References
