Lorenz System Parameter Determination and Application to Break the   Security of Two-channel Chaotic Cryptosystems
  This paper describes how to determine the parameter values of the chaotic Lorenz system used in a two-channel cryptosystem. The geometrical properties of the Lorenz system are used firstly to reduce the parameter search space, then the parameters are exactly determined, directly from the ciphertext, through the minimization of the average jamming noise power created by the encryption process. 
A. B. Orue, G. Alvarez, M. Romera, G. Pastor, F. Montoya and Shujun Li