[rodgerd]

Not a crypto expert either, but from what I've gleaned listening to e.g. Peter Guttman describe evaluating new crypto mechanisms, you'll see that:

1. Actual cryptographers usually design with a set of constraints that make their crypto work: those might be about compute power, or memory bandwidth, or what have you, that make an algorithm difficult to brute force.

2. The algorithm will typically be peer-reviewed to try to weed out mistakes, either fundamental mathematical ones, or in the assumptions.

3. The implementation then needs to be high quality.

There are certainly no shortage of examples where systems which pass 1 & 2 are undermined by failures in 3. All algorithms are susceptible to the context around 1 changing (changes in compute power or whatever).

When you go it alone, you're assuming that you won't make any mistakes any of these. That seems a pretty tall order.