I'm working on an algorithm of a block cipher. One step of this algorithm is to build m*m bijective functions (here: m = 4). Earlier I assumed it means the input and output should be 4 bits respectively. But this understanding didn't fit in the algorithm well. According to the algorithm, there's a definition of bijective functions.
Anyone has an idea about the m*m bijective functions? Any pointer would be appreciated. Thanks in advance!