So, I'm not sure if I'm being too simple-minded in my response. Please let me know if I am.
The purpose of encrypting data is so others can't read your secrets.
If you use a simple substitution cipher it's pretty easy to derive the set of substitution rules used.
Stronger encryption algorithms employ more "difficult" math. Figuring out how to get from the ciphertext to the plaintext becomes a, computationally, difficult task.
If your encryption algorithms are "good" *and* your source of random data is really random then the amount of time it takes to decrypt the data is so far out that it makes the data useless.
Cheers,
Harry