Researchers Simplify Quantum Cryptography

Stony Stevenson writes "Quantum cryptography, the most secure method of transmitting data, has taken a step closer to mainstream viability with a technique that simplifies the distribution of keys. Researchers at NIST claim that the new 'quantum key distribution' method minimizes the required number of detectors, the most costly components in quantum crypto. Four single-photon detectors are usually required (these cost $20K to $50K each) to send and decode cryptography keys. In the new method, the researchers designed an optical component that reduces the required number of detectors to two. (The article mentions that in later refinements to the published work, they have reduced the requirement to one detector.) The researchers concede that their minimum-detector arrangement cuts transmission rates but point out that the system still works at broadband speeds."

Re:what's the big deal

[Anonymous Coward]

It is impossible to crack because there is no way to decode it without the right key. Algorithms like RSA or DES can be brute forced with enough horse power, for instance, when the quantum computer is invented it could make short work of them. Quantum cryptology will be the only defense.

Re:what's the big deal

[BadAnalogyGuy]

The big deal is that the cracking time for non-quantum algorithms reduces to O(n) for length n keys. OTOH, for quantum encryption, the cracking time minimum threshold is O(n^n) for length n keys. Hyperbolically, the linear analog is also true in that with quantum decryption, it is possible to crack non-quantum algorithms in O(n) time (again for length n keys), but quantum algorithms require O(n^n) to decrypt. Note that without the correct key, the quantum algorithm requires O(n^n) regardless of whether the cracker is employing spherical numerical analysis techniques or advanced quantum distribution array matrices.

The fact of the matter is that quantum encryption provides much greater security than standard algorithmic encryption.

Re:what's the big deal

[Inf0phreak]

I think you've misunderstood something. "Quantum encryption" is something of a misnomer. It's actually a physical process that can be used by Alice and Bob to establish a commonly shared secret that is random (and unknown to even Alice and Bob before the process starts). This secret is then typically used as a one-time pad [wikipedia.org].

Not much

[Mathinker]

From Wikipedia:

Quantum encryption technology provided by the Swiss company Id Quantique was used in the Swiss canton (state) of Geneva to transmit ballot results to the capitol in the national election occurring on Oct. 21, 2007.[8]

In 2004, the world's first bank transfer using quantum cryptography was carried in Vienna. An important cheque, which needed absolute security, was transmitted from the Mayor of the city to an Austrian bank.[9]

Both of these look like special uses set up for publicity by vendors.

Re:what's the big deal

[SeekerDarksteel]

The reason Eve can't just generate a new pad is because there are two methods of generating a photon and two methods of measuring a photon. Each method of generating a photon has a matched way of measuring it. If you use the matched measurement method you correctly get the bit Alice sent. If you use the incorrect method you get a random 0 or 1 no matter what bit Alice sent. Eve (and Bob too) has no way of telling which method Alice used. In quantum key distribution, after sending the photons, Alice would contact Bob over a different channel. They would tell which method they used, and if they used matching methods keep that bit. If they used different methods they would throw out the bit. If Eve regenerated the bits, she could not have used the same methods as Alice since she doesnt know which methods were used. So Alice and Bob's keys won't match up which will result in any information passed between them to be undecodable and they will know someone eavesdropped.

Quantum Key Distribution is, in its most naive form, still vulnerable to man in the middle attacks. It makes it a little more difficult because you must be able to intercept information on two different channels (the quantum channel and the classical electronic channel), but it is still doable. (There are, however, cryptographic methods of detecting man in the middle attacks, but thats a subject for another time).

Re:Not the most secure

[Cairnarvon]

-1 Failed Attempt at Sounding Insightful.
Quantum cryptography schemes are guaranteed to inform both Alice and Bob if their communication is intercepted. That's the entire point, and what has everyone so excited about quantum cryptography in the first place. Secrecy in the sense of undecryptability isn't the point of quantum cryptography (as data isn't even *encrypted* in the classical sense), just certainty that there are no eavesdroppers.
Your post just suggests that you haven't actually read anything about quantum cryptography, you've just heard something about one-time pads and thought this would be a good time to misapply your knowledge.

Quantum cryptography isn't a cipher. It's a method of transmitting data, which does one specific thing, which is guarantee that you'll be able to tell if people have attempted to eavesdrop.
It's not a complete cryptosystem; it's not meant to be. It's meant to be just one component of cryptosystems, and in doing what it does, it's provably secure in the sense that secure is being used here.

(Incidentally, mathematical proofs aren't like scientific proofs; it *is* possible to prove with absolute certainty in mathematics.)

Re:what's the big deal

[khellendros1984]

From what I understand, quantum computing will basically allow the equivalent of massively parallel computation, so you can find the key that solves the message easily. In RSA, it means that it could factor the large prime numbers that make up the public key, and mathematically generate the private key from those.

Re:what's the big deal

[arotenbe]

"Conventional" encryption algorithms can be brute forced even without the correct key - it will just take a really long time. As I understand it, the point of quantum cryptography is that it is completely impossible to break, because the transmission would be scrambled the moment someone tries to tap the connection.

Don't expect the above to be completely correct, though - I'm hardly a cryptography expert (which doesn't stop me from putting a reference in my sig [wikipedia.org]).

Re:what's the big deal

[mapsjanhere]

People are mixing up two different things here - quantum transmission, the one you can't read unnoticed, and encryption/decryption using quantum computers and algorithms.
The first one has been demonstrated, and works over limited distances.
The second is an "advanced concept", right next to fusion reactors.

Mod parent up

[bh_doc]

I was just discussing entanglement swapping with my supervisor the other day, actually. Neat concept. Roughly, person A has two entangled photons, A1 and A2. Person B has similar, B1 and B2. They both send their 1 photons to C. C entangles A1 and B1 and because of this, A2 and B2 are now entangled. This can then be used to generate a bit of a key.

We were actually discussing it in the context of producing entanglement between ions (good for storage/memory) and photons (good for transmission), since in the real-world it's unlikely actual repeaters will receive photons from both parties at the same time so that the entanglement can be swapped.