Except if it's really random, after enough trials you'll have some clearly random distribution, with some distortion related to the actual cost. Figuring out th

Except if it's really random, after enough trials you'll have some clearly random distribution, with some distortion related to the actual cost. Figuring out the cost is just some statistical analysis away. See e.g. https://crypto.stanford.edu/~dabo/papers/ssl-timing.pdf https://crypto.stanford.edu/~dabo/papers/ssl-timing.pdf for this principle applied to performing timing attacks on a remote server (so network latency serves as a handy-dandy rng).