With WTC algorithm developed by Weiss, Tabor and Carnevale, we concluded that a nonlinear vibrating string equation has Painlevé property. Bäcklund transformation is obtained. Furthermore, soliton fusion is analyzed by means of Hirota's direct method and Bäcklund transformation.

An encryption approach based on chaos in semiconductor lasers with electro-optical delayed feedback loop is proposed. To mask plaintext, we use chaotic map of semiconductor lasers subject to electro-optical feedback modeled by Ikeda equations to generate binary sequences. The plaintext block is permuted by a key-dependent shift approach and then encrypted by a classical chaotic masking technique. In each encryption turn, feedback is perturbed by a random number which depends on chaotic map, plaintext and ciphertext. State transfer function depends not only on the secret key, but also on the input plaintext of the turn and output ciphertext of the last turn to avoid chosen plaintext/ciphertext attack. Simulations show that the proposed cryptographic scheme is feasible and effective.