Is there a mechanism to use HTTPS to preencrypt web pages so that they are encrypted on the server (and so the server does not have the keys to decrypt them!)
Not using HTTPS per-se, but you can use SSL to encrypt files.
My initial constraints are that once the data is put on the server that no one except forthe intended recipient could decrypt it, including the original poster, server admin...
Or, to basically do with HTTP what GPG does with email. The original poster would necessarily need to have access to the plaintext, as they would need to encrypt it with the end-user's public keys (each of them individually).
I'm not a mathematician, but it can't be wise to store multiple copies of the same plaintext encrypted by the same cipher using different keys .. much crypto has historically been broken that way.
~Mike.