A question on public/private key encryption

[aa0]

Why can't the private key be cracked by encrypting a large enough block of static data, all bits=1 for example, with the public key?

[deanfranks]

If the cypher being used is secure, encrypting a block of 1s or 0s will generate an apparently random stream of 0s and 1s. There will be no way to determine the private key from the output of encrypting a block of known data with the public key.

[aa0]

Couldn't a cross-comparison be used, encrypting different known blocks and observing certain key properties? I would imagine that any kind of reversible operation would be able to be deduced if it can be applied to specific data that reveals its true form/operation.