Characterization of Collective Gaussian Attacks and Security of   Coherent-State Quantum Cryptography
  We provide a simple description of the most general collective Gaussian attack in continuous-variable quantum cryptography. In the scenario of such general attacks, we analyze the asymptotic secret-key rates which are achievable with coherent states, joint measurements of the quadratures and one-way classical communication. 
Stefano Pirandola, Samuel L. Braunstein, and Seth Lloyd