Is there any tool available that can test whether a simple substitution cipher is working. I will put my scenario in detail. Lets say I built a simple substitution cipher that maps 8 bit data to 16 bit encrypted cipher using an 8 bit key. I need to verify whether the substitution cipher is actually unique for all possible permutations of 8 bit data and 8 bit keys with my algorithm.
Before you guys eat me alive with 'You think you can build a superior cipher?' questions, this is not a high security application but a simple app where sending plain data is not preferred. Existing ciphers like columnar transposition and caesar cipher were not an option considering user experience and ease of implementation. You can assume it is just simple XOR.
I just want to verify whether the substitution is happening correctly or not. If I need to manually write a program that can verify this, can anyone give me a brief detail about how I should start?