This is the reference implementation in C of 4096XKS-F block cipher, it is extracted from its paper: https://eprint.iacr.org/2013/136
4096XKS-F is a high security block Feistel cipher with a block length of 4096 bits and a key size of 8192 and 16384 bits, respectively.
4096XKS-F is free, but this reference implementation is covered by the GNU General Public License.