Is there any alternative for cryptography? I heard a lot about quantum cryptography, but is this the only stuff which have a chance to exist in the future? Are there any other kinds of cryptography?
I'm really trying to guess what you mean by this question. However, I'll try to answer. I think that you are wondering what other methods could cryptography use. Like quantum cryptography uses quantum mechanics.
A few days ago, Laszlo Kish showed another way to send information - based on thermodynamic laws.
You can read more here.
Cryptography is already an alternative, namely to "physical security systems":
- Confidential data can be written on some convenient medium, which is stored in a big safe.
- Confidential data can be entrusted to a speedy messenger, who travels with a squad of mean-looking bodyguards.
- Non-repudiation is achieved by having the signer take a solemn oath under scrutiny of duly appointed witnesses (e.g. notaries), and you can always have some goons break the thumbs of defaulters.
- Voting -- well, that one is done with bits of paper in boxes, cryptography has not even yet achieved the status of "viable alternative" for that.
Such things have been done since the invention of writing, a good 5000 years ago. Cryptography just allows to do these things faster and cheaper and farther. But this means that, should cryptography fail, you could always revert to the Old Style ways known since the days of Pharaoh, and which ultimately sum up as: just throw more money at it(*).
"Quantum cryptography" means two things:
the boring key exchange system, which works in practice but solves no problem which did not already had a convenient classical solution (and which, still in practice, turns out to be quite difficult to do without adding some extra weaknesses);
the exciting new calculus model, which is totally awesome and utterly wrecks the common asymmetric algorithms (RSA and Diffie-Hellman based systems, including elliptic curves) but has the slight disadvantage of not working at all in practice (a minor setback, to be sure -- but we have no idea whatsoever on how to work around it). Also, that kind of quantum cryptography does not completely kill symmetric cryptography (symmetric encryption, hashing...), so we can still do some cryptography in a post-QC world (including signatures, with Merkle's scheme).
(*) Ok, ok, I admit: there was no actual money in Ancient Egypt; the economic system was based on generalized barter, and the first use of actual currency appears only during the 5th century BC. Just imagine that Pharaoh's messengers were paid in wheat and beer.