My original problem: I want Alice to be able to promise that at some point in the future she will upload a statement to an address in a hash-table, which is computable/predictable from everyone without knowing her secret key (to be able to look at that address, if the statement is already there). However, the statement should not be predictable for everyone.
One solution path:
Alice has a secret key $S$ and the corresponding public key $P$ (solutions for any (secure) key generation algorithms are appreciated). Is there any combination of (any) functions $f_1, f_2$ and (any) hashing algorithms $h_1, h_2$, s.t. the following holds?
$h_1(f_1(P)) = h_2(f_2(S, P))$
I.e. an algorithm that gives a predictable hash for data generated by the secret key. A hash that can be generated from the public key only, which will be the same for a string generated from the secret (and possibly the public) key.
Important note: $f_1$ may not be aware of $S$, of course, and $f_2$ may not ignore $S$. Otherwise there are of course trivial solutions...
My question: Can my proposed solution be workable or is there a better way to accomplish this?