How do you measure the strength of an encryption algorithm? So far, I have not found a complete reference on this. There are some references and they refer to different things, such as randomness, avalanche effect, diffusion, or anything that is related to how different the output if the input or key is very similar. Another issue that is important is the key space. The larger the key space and the more complex the algorithm (big Oh?), the more difficult an algorithm is broken by brute force attack. Another lead says that you have to go through cryptanalysis to measure the strength of an encryption algorithm. Anyway, I am still searching. Let me know if you have more references.