In cryptography, CS-Cipher (for Chiffrement Symétrique) is a block cipher invented by Jacques Stern and Serge Vaudenay in 1998. It was submitted to the NESSIE project, but was not selected. The algorithm uses a key length between 0 and 128 bits (length must be a multiple of 8 bits). By default, the cipher uses 128 bits. It operates on blocks of 64 bits using an 8-round Feistel network and is optimized for 8-bit processors. The round function is based on the fast Fourier transform and uses the binary expansion of e as a source of "nothing up my sleeve numbers".
References J. Stern, S. Vaudenay (1998). "CS-Cipher". Archived from the original (PostScript) on 2004-11-27. Retrieved 2007-02-15.