# Researchers Simplify Quantum Cryptography

#### kdawson posted more than 6 years ago | from the again-with-the-bob-and-alice dept.

106
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."*

## Quantum Post! (5, Funny)

## Majik Sheff (930627) | more than 6 years ago | (#23634813)

## Re:Quantum Post! (-1, Offtopic)

## Anonymous Coward | more than 6 years ago | (#23635059)

## Re:Quantum Post! (1, Funny)

## Anonymous Coward | more than 6 years ago | (#23636973)

## Re:Quantum Post! (5, Funny)

## FrYGuY101 (770432) | more than 6 years ago | (#23635121)

## Re:Quantum Post! (1)

## mrsteveman1 (1010381) | more than 6 years ago | (#23635145)

## Re:Quantum Post! (0)

## Anonymous Coward | more than 6 years ago | (#23636171)

## Re:Quantum Post! (2, Funny)

## calmond (1284812) | more than 6 years ago | (#23636101)

## Re:Quantum Post! (1, Funny)

## Anonymous Coward | more than 6 years ago | (#23636839)

## Actually... (1)

## RudeIota (1131331) | more than 6 years ago | (#23635499)

## Re:Actually... (2, Interesting)

## Impy the Impiuos Imp (442658) | more than 6 years ago | (#23638329)

Hey wait, that shouldn't be possible.

> Quantum cryptography, the most secure method of transmitting data,

Technically it would only be tied at best with a one-time pad, and, at worst, slightly less secure. I wonder if it has codes that could be cracked by social engineering, as one time pad's could, or if you must physically have the proper connection device.

But I hear it's also possible to do a quantum simulation of the entire universe using a quantum device. Hence it may be trivial to crac...hey, waitaminnit!

Maybe this whole universe is someone's attempt to quantum crack some encoded pr0n. DAMMIT!

DAMMIT! My life is just being a cog in someone's un-encoding of some pr0n! >:(

Actually, I feel my life is more valuable doing that then it turning out this universe was Yahweh's twice-patched fuckup (Noah, and Jesus) wise and perfect plan all along.

## Entangled (-1, Offtopic)

## Anonymous Coward | more than 6 years ago | (#23634815)

## Re:Entangled (1)

## datapharmer (1099455) | more than 6 years ago | (#23636465)

## what's the big deal (0)

## ILuvRamen (1026668) | more than 6 years ago | (#23634843)

## Re:what's the big deal (2, Informative)

## Anonymous Coward | more than 6 years ago | (#23634905)

## Re:what's the big deal (0)

## mrbluze (1034940) | more than 6 years ago | (#23635043)

Maybe not. IANAC (I am not a cryptographer) but my limited understanding of things is that quantom computing is not the be-all-and-end-all of encryption. It

ispossible to develop encryption algorithms that run on conventional processors which are resistant to what quantum computers areprobablygoing to be capable of doing with numbers.I don't have the vocabulary to go beyond that at this time of day but a while back while almost-blind-drunk I had one of those moments of clarity and it all made sense.

## Re:what's the big deal (2, Informative)

## khellendros1984 (792761) | more than 6 years ago | (#23635459)

## Re:what's the big deal (3, Informative)

## arotenbe (1203922) | more than 6 years ago | (#23635467)

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 (1)

## ark1 (873448) | more than 6 years ago | (#23639557)

## Re:what's the big deal (1)

## Super Jamie (779597) | more than 6 years ago | (#23635103)

## Re:what's the big deal (1)

## mattmcm (1143125) | more than 6 years ago | (#23636977)

## Re:what's the big deal (1)

## Tanktalus (794810) | more than 6 years ago | (#23638117)

Who cares? I want to know if it will run Duke Nukem Forever!

## Re:what's the big deal (5, Informative)

## BadAnalogyGuy (945258) | more than 6 years ago | (#23634917)

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

## Re:what's the big deal (5, Interesting)

## Anonymous Coward | more than 6 years ago | (#23635029)

This is all nice, but it is going to be tricky to implement it in the future. How do you send a photon from one computer to another a long distance away without using repeaters or branches? It will be a little tricky. Would this require a fiber optic connection between every computer that wants to communicate with quantum encryption? Or can you adjust the medium so that photons are transmitted and branched undisturbed?

## Re:what's the big deal (3, Informative)

## mapsjanhere (1130359) | more than 6 years ago | (#23637649)

The first one has been demonstrated, and works over limited distances.

The second is an "advanced concept", right next to fusion reactors.

## Re:what's the big deal (1)

## kmac06 (608921) | more than 6 years ago | (#23644169)

Also you can control/change the path of the photon using electro-optical controls without changing it's state (or at least without changing the part of the state that carries the information), though this would likely be more difficult/expensive to implement on a wide scale.

## Re:what's the big deal (2, Funny)

## SeekerDarksteel (896422) | more than 6 years ago | (#23635357)

## Re:what's the big deal (1)

## NormalVisual (565491) | more than 6 years ago | (#23636909)

## Re:what's the big deal (2, Insightful)

## spazdor (902907) | more than 6 years ago | (#23635373)

I was with you up until about there. It occurs to me that there are any number of mathematical terms that could be combined at random to induce the same effect in me, and I wonder if this is true of all the people who modded you up.

I think i'm just gonna take your word for it.

## Re:what's the big deal (3, Funny)

## MrMr (219533) | more than 6 years ago | (#23635411)

spherical numerical analysis techniques: That is standard maths; If you need to compute something involving for instance a cow, you start with "Assume a spherical cow with radius R".advanced quantum distribution array matrices: That just your normal quantum distribution array matrices but with the new icons and toolbar.## Re:what's the big deal (1)

## redxxx (1194349) | more than 6 years ago | (#23636679)

## Re:what's the big deal (1)

## beckerist (985855) | more than 6 years ago | (#23638323)

## Re:what's the big deal (1)

## jonaskoelker (922170) | more than 6 years ago | (#23637011)

Uniform density!

## Re:what's the big deal (0)

## Anonymous Coward | more than 6 years ago | (#23641381)

## Re:what's the big deal (1)

## gweihir (88907) | more than 6 years ago | (#23636315)

The fact of the matter is that quantum encryption provides much greater security than standard algorithmic encryption.In your dreams. No quantum computer exists that can break encryption used today by a very, very large margin. It seems doubtful whether researchers can get beyond a few bits at all, let alone scale up to a few thousands. Presently this is all hype to get research money. There have been much more similar things that failed and only very few that deliverd on their claims.

## Re:what's the big deal (2, Insightful)

## devman (1163205) | more than 6 years ago | (#23636655)

## Re:what's the big deal (1)

## Tolkien (664315) | more than 6 years ago | (#23637033)

## Re:what's the big deal (1)

## kmac06 (608921) | more than 6 years ago | (#23644261)

Parent shouldn't be modded informative, just about everything he said was wrong.

## Re:what's the big deal (0)

## Anonymous Coward | more than 6 years ago | (#23634925)

## Re:what's the big deal (4, Informative)

## Inf0phreak (627499) | more than 6 years ago | (#23634935)

## Re:what's the big deal (1)

## menace3society (768451) | more than 6 years ago | (#23634973)

## Re:what's the big deal (1)

## Firehed (942385) | more than 6 years ago | (#23634997)

That's my best guess, I've never really understood the theory either. It IS quantum physics, after all.

## Re:what's the big deal (5, Informative)

## SeekerDarksteel (896422) | more than 6 years ago | (#23635111)

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:what's the big deal (1)

## devman (1163205) | more than 6 years ago | (#23636697)

## Re:what's the big deal (1)

## Urkki (668283) | more than 6 years ago | (#23635203)

Somebody correct me if I'm badly mistaken...

## Re:what's the big deal (2, Interesting)

## locofungus (179280) | more than 6 years ago | (#23635849)

Here's something I've never understood. Alice prepares a one-time pad and sends it along using this quantum dealie. Eve intercepts it. Now supposedly this thing changes every time someone observes it, but could Eve just generate a new one based on the data she acquired? Alice created one 'from scratch', why can't Eve?Lookup quantum cloning and the "no cloning theorem".

But basically (and this is a naive implementation that won't actually work), Alice transmits to Bob using linearly polarized photons. Now, if you remember from your school days, if you shine a light though a polarization filter and then through another filter at the same angle, all the light that gets through the first filter gets through the second filter as well.

So, let Alice transmit a horizontally polarized photon |H> if she wants to send a 1 and |V> if she wants to send a 0.

Bob uses a horizontally polarized filter = 1 (the photon gets through and he detects it, = 0. The photon gets stopped and he doesn't detect it.

So far, so good but... Eve does exactly what you suggested and measures the photon and then regenerates it - so Bob doesn't see any difference.

Now it starts getting clever

So as well as using |H>,|V> to transmit 1 and 0, Alice also uses |+>,|-> where these are 45 degree polarizations. Alice uses one or the other completely at random.

Bob, when he measures at his end also choses whether to measure the horizontal polarization = Alice and Bob use the same polarization angle so Bob detects the photon

= Alice and Bob use crossed polarization filters so Bob doesn't detect the photon

= Alice and Bob's filters are at 45 degrees so Bob may or may not detect a photon

= ditto

= ditto

= ditto

= Alice and Bob use the same polarization angle so Bob detects the photon

= Alice and Bob use crossed polarization filters so Bob doesn't detect the photon

Once Alice and Bob have done this, Bob tells Alice which measurement he's done (over a classical channel, they don't care who might eavesdrop.) If Alice and Bob have used the same basis - i.e. Alice used |H>,|V> to transmit her bit and Bob used

Now Eve can get really clever. Instead of measuring the photon, she can clone it and then measure her clone. Now it turns out that there is a limit to how good her cloning machine can be so, although it won't corrupt half of the bits that Alice and Bob transmit, it will corrupt at least 1/6.

(Actually, in the naive scheme outlined above I think Eve can do:

a|H> + b|V> => a|HH> + b|VV>, store her photon, wait for Bob to measure, eavesdrop the message from Bob to Alice and then make the same measurement on her stored photon. But this only works because the only possible values for a,b in the naive scheme are (0,1), (1,0), (1/sqrt2,1/sqrt2), (1/sqrt2, -1/sqrt2) but I'm right on the limits of my understanding of QM and entangled photons now so I could be completely wrong)

Tim.

## Re:what's the big deal (1)

## ArsenneLupin (766289) | more than 6 years ago | (#23637221)

afterBob has measured the quantum bits. So, even can't just store them, measure them and re-inject them after the fact.So, rather than just eavesdropping the message from Bob to Alice, she would actually need to destructively intercept it and change it.

## Re:what's the big deal (1)

## locofungus (179280) | more than 6 years ago | (#23642549)

Actually, the message telling which bits were send and/or measured at a 45% angle is only exchanged after Bob has measured the quantum bits. So, even can't just store them, measure them and re-inject them after the fact.

So, rather than just eavesdropping the message from Bob to Alice, she would actually need to destructively intercept it and change it.

Eve isn't intercepting the bits. She's creating a pair of correlated photons without actually making any measurement. She sends one on to Bob and stores the other for measuring later.

a|H> + b|V> => a|HH> + b|VV>. I'm pretty sure this transformation is allowed for all values of a and b. Note that she is NOT cloning (a|H> + b|V>)(a|H> + b|V>) which would be prohibited.

Having said that, I think my quick thoughts were incorrect. I was assuming

|HH> = k|++> + k|--> when I think it should have been 1/2|++> + 1/2|+-> + 1/2|-+> + 1/2|-->

(k=1/sqrt2) now that I think about it properly.

Tim.

## Re:what's the big deal (1)

## locofungus (179280) | more than 6 years ago | (#23635871)

Here's something I've never understood. Alice prepares a one-time pad and sends it along using this quantum dealie. Eve intercepts it. Now supposedly this thing changes every time someone observes it, but could Eve just generate a new one based on the data she acquired? Alice created one 'from scratch', why can't Eve?Lookup quantum cloning and the "no cloning theorem".

But basically (and this is a naive implementation that won't actually work), Alice transmits to Bob using linearly polarized photons. Now, if you remember from your school days, if you shine a light though a polarization filter and then through another filter at the same angle, all the light that gets through the first filter gets through the second filter as well.

So, let Alice transmit a horizontally polarized photon |H> if she wants to send a 1 and |V> if she wants to send a 0.

Bob uses a horizontally polarized filter <H| to measure Alice's photon. <H|H> = 1 (the photon gets through and he detects it, <H|V> = 0. The photon gets stopped and he doesn't detect it.

So far, so good but... Eve does exactly what you suggested and measures the photon and then regenerates it - so Bob doesn't see any difference.

Now it starts getting clever

So as well as using |H>,|V> to transmit 1 and 0, Alice also uses |+>,|-> where these are 45 degree polarizations. Alice uses one or the other completely at random.

Bob, when he measures at his end also choses whether to measure the horizontal polarization <H| or diagonal polarization <+| completely at random. There are eight cases:

<H|H> = Alice and Bob use the same polarization angle so Bob detects the photon

<H|V> = Alice and Bob use crossed polarization filters so Bob doesn't detect the photon

<H|+> = Alice and Bob's filters are at 45 degrees so Bob may or may not detect a photon

<H|-> = ditto

<+|H> = ditto

<+|V> = ditto

<+|+> = Alice and Bob use the same polarization angle so Bob detects the photon

<+|-> = Alice and Bob use crossed polarization filters so Bob doesn't detect the photon

Once Alice and Bob have done this, Bob tells Alice which measurement he's done (over a classical channel, they don't care who might eavesdrop.) If Alice and Bob have used the same basis - i.e. Alice used |H>,|V> to transmit her bit and Bob used <H| to measure it or Alice used |+>,|-> to transmit her bit and Bob used <+| to measure it then Alice says "correct" and Bob knows what bit Alice sent. If Bob used the wrong measurement then Alice says "incorrect" and they both throw that bit away.

So, on average, for each two bits that Alice tries to send to Bob, one will be thrown away and the other will be a good value.

Now Eve tries to eavesdrop. If she measures <H| then she'll detect |H> or |V>. She can retransmit that value but, if Alice sent |+> or |-> instead then she'll have corrupted the bit. If she measures <+| instead then she can retransmit |+> or |-> but if Alice sent |H> or |V> then she'll corrupt that bit instead. Infact, on average, regardless of which measurement she makes, she'll end up corrupting 1/2 of the values that Alice and Bob have "successfully" exchanged.

Now Eve can get really clever. Instead of measuring the photon, she can clone it and then measure her clone. Now it turns out that there is a limit to how good her cloning machine can be so, although it won't corrupt half of the bits that Alice and Bob transmit, it will corrupt at least 1/6.

(Actually, in the naive scheme outlined above I think Eve can do:

a|H> + b|V> => a|HH> + b|VV>, store her photon, wait for Bob to measure, eavesdrop the message from Bob to Alice and then make the same measurement on her stored photon. But this only works because the only possible values for a,b in the naive scheme are (0,1), (1,0), (1/sqrt2,1/sqrt2), (1/sqrt2, -1/sqrt2) but I'm right on the limits of my understanding of QM and entangled photons now so I could be completely wrong)

Tim.

## Re:what's the big deal (1)

## ILuvRamen (1026668) | more than 6 years ago | (#23635005)

## Re:what's the big deal (1)

## locofungus (179280) | more than 6 years ago | (#23635925)

The best that Eve can do is a DOS attack.

Tim.

## Re:what's the big deal (1)

## amrik98 (1214484) | more than 6 years ago | (#23634953)

## Impossible to eavesdrop, otherwise, a big yawn (5, Interesting)

## Mathinker (909784) | more than 6 years ago | (#23634955)

Otherwise, you are perfectly correct. Many cryptographers, including Bruce Schneier, believe that quantum cryptography is a solution to the wrong problem. Nowadays, most probably, the least secure part of your communication system isn't in your key distribution scheme, but is somewhere else --- like in social engineering, or the computer systems which deal with the decrypted cleartext.

## Re:Impossible to eavesdrop, otherwise, a big yawn (0)

## Anonymous Coward | more than 6 years ago | (#23635239)

## Re:Impossible to eavesdrop, otherwise, a big yawn (1)

## Tom (822) | more than 6 years ago | (#23636693)

## Re:what's the big deal (1)

## gweihir (88907) | more than 6 years ago | (#23636293)

## What are you doing here (-1, Flamebait)

## Anonymous Coward | more than 6 years ago | (#23634847)

## Re:What are you doing here (-1, Offtopic)

## Anonymous Coward | more than 6 years ago | (#23634857)

## Re:What are you doing here (2, Funny)

## BlockedThreads (870266) | more than 6 years ago | (#23635017)

## Real world usage? (1, Offtopic)

## BadAnalogyGuy (945258) | more than 6 years ago | (#23634873)

## Not much (3, Informative)

## Mathinker (909784) | more than 6 years ago | (#23635015)

## Re:Not much (1)

## gweihir (88907) | more than 6 years ago | (#23636335)

Both of these look like special uses set up for publicity by vendors.They are. Nobody competent would use quantum techniques for things that really need to be secure. The physics is not that well established, for one thing, leading to an unknown risks. Sure, the properties look nice, but when was the last time a fundamental physical theory turned out to be not quite accurate? Yes, that is true, when the current theory replaced the last one. That has happened so far to every theory except the respective current last ones. Why should there not be additional theory refinements? And the current theory was emphatically not made to predict any security properties. It is more a result of some physics people trying their hand at philosophy (and failing IMO).

## I doubt it. (0, Redundant)

## jd (1658) | more than 6 years ago | (#23635045)

## Yep! Re:Real world usage? (1)

## Invisible Now (525401) | more than 6 years ago | (#23635451)

Google it...

or check this: http://it.slashdot.org/article.pl?sid=06/12/13/1458238&from=rss [slashdot.org]

## Re:Real world usage? (0)

## Anonymous Coward | more than 6 years ago | (#23635931)

Like between the control bunker and the launch pad.

Presumably to prevent hot wiring.

## Yay! Saved! (1, Funny)

## SEWilco (27983) | more than 6 years ago | (#23634919)

## Oblig XKCD (3, Funny)

## azakem (924479) | more than 6 years ago | (#23634947)

## Broadband Speeds (1, Interesting)

## enoz (1181117) | more than 6 years ago | (#23634991)

For reference, in Australia not only does the incumbent Telco consider 256/64kbps to be broadband, but they also describe it as "Fast [bigpond.com] ".

## Re:Broadband Speeds (1)

## TubeSteak (669689) | more than 6 years ago | (#23635291)

The whole point is to be able to securely pass an encryption key.

Then you can encrypt and use any method you like for transporting the encrypted data.

Whether it's Australian 'fast', Internet2 fast, or a stationwagon full of Terabyte hard drives fast.

## Broadband? (1, Insightful)

## Tubal-Cain (1289912) | more than 6 years ago | (#23635013)

## Re:Broadband? (1)

## Tubal-Cain (1289912) | more than 6 years ago | (#23635225)

## Re:Broadband? (1)

## spazdor (902907) | more than 6 years ago | (#23635399)

## Not the most secure (2, Insightful)

## BlueParrot (965239) | more than 6 years ago | (#23635061)

In practice none of this is relevant since the hassles associated with correctly implementing either QC or a OTP are sufficiently large that for most applications they are both inferior to public key cryptography and symmetric ciphers. There are some exceptions, but the only way you could possibly justify describing quantum cryptography as "the most secure way to transmit data" would be by ignoring so many aspects of information security that it will have no relevance to practical applications.

## Re:Not the most secure (2, Informative)

## Cairnarvon (901868) | more than 6 years ago | (#23635147)

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:Not the most secure (2, Interesting)

## Creepy Crawler (680178) | more than 6 years ago | (#23635351)

Or better yet, what would happen if some new device could record without observing?

---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.

Of course not. quantum crypto solves the problem with OTP's: secure transmission of the OTP lookup sheet itself. I forget the bit rate of the machine, but it's something damned slow (100 bits/s?). The ultimate problem with any crypto system is still the people though. Too bad it doesnt fix that ^_^

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

Also, unfortunately, QC math isnt a math proof. It's a proof on physics that attempts to estimate the real math of our universe. Until we know the "real" math, there will be holes in our knowledge, and therefore unprovable. It's probably pretty accurate though, but is it accurate to trust?

## Re:Not the most secure (1)

## Cairnarvon (901868) | more than 6 years ago | (#23635687)

I spend most of my time debating creationists, not laypersons who misunderstand quantum physics, but I bet physicists get as tired of shouting "IT DOESN'T WORK LIKE THAT" at people like you as I do at creationists.

You'll remember Feynman once compared our understanding of quantum physics to measuring the distance between New York and Los Angeles to within the width of a human hair. I'd say anything with that kind of predictive power is probably accurate enough to trust your life with.## Re:Not the most secure (1)

## blueg3 (192743) | more than 6 years ago | (#23637219)

## Re:Not the most secure (1)

## locofungus (179280) | more than 6 years ago | (#23635965)

Or better yet, what would happen if some new device could record without observing?"record without observing" doesn't make sense. In the words of Pauli, "That's not right. That's not even wrong." But trying to guess that you mean "observe without affecting in any way".

Then you can violate causality. Give me a device that can "record without observing" and I'll build you a device to communicate faster than the speed of light.

Tim.

## Re:Not the most secure (0)

## Anonymous Coward | more than 6 years ago | (#23635153)

So. Uh. What were you saying again?

## Apples and oranges (2, Interesting)

## Chuck Chunder (21021) | more than 6 years ago | (#23635227)

You are comparing apples with oranges. The bit your mathematician can "prove" is only part of the problem quantum encryption aims to solve. Ie quantum encryption also includes key exchange (and in fact typically uses a one time pad for the data transfer).

You can't simply ignore the key exchange problems on the mathematicians side.

Perhaps the laws of physics that are supposed to protect quantum encryption will turn out to be false but based on our current understanding there is no better way to do it.

How is your mathemetician going to distribute his one time pad?

## Re:Apples and oranges (2, Interesting)

## Creepy Crawler (680178) | more than 6 years ago | (#23635323)

A one time pad guarantees perfect secrecy. A QC channel allows secrecy as any "listening" devices become in part with the system, thereby allowing detection.

I do think this is a bit excessive by stating.. Data is always time-dependent. Therefore, we only need protect data for X amount of years.

What combination of encryption technologies can we use to make the data physically hard to crack? We need a multi-tiered encryption setup that uses multiple algorithms and multiple layers. Assuming mathematical proof of said encryption and no holes in implementation, we can calculate CPU years in brute-forcing each layer. Also, assuming that MIPS/s is increasing exponentially, we can calculate a "cracked by" date, and wrap said data in the date we need.

Having "perfect" data integrity and "perfect" communication seems... not right. It's just a gut feeling.

## Re:Apples and oranges (0)

## Anonymous Coward | more than 6 years ago | (#23635567)

Having "perfect" data integrity and "perfect" communication seems... not right. It's just a gut feeling.

## Re:Apples and oranges (1)

## Creepy Crawler (680178) | more than 6 years ago | (#23637875)

## Re:Apples and oranges (1, Insightful)

## Anonymous Coward | more than 6 years ago | (#23635545)

The same way you are going to tell the receiver of the QC message to use Quantum cryptography in the first place.

Lots of people seem to have this confused. Quantum cryptography does NOT give you a way to do secure key exchange without meeting the person you are going to communicate with. If you think about it for a second you will realize that this CANNOT be done no matter what encryption scheme, and no matter what "spooky action at a distance" you come up with. No matter what encryption scheme I use to communicate with you, I first need to agree with you to use that scheme, or for that matter, I have to get to know you for the concept of "you" to even make sense. If we have agree to an encryption scheme, we could just as well have exchanged one time pads, or RSA public keys, while doing it.

To put it this way, I made this post, but there is NO way for you to EVER determine who I was. Quantum cryptography won't do it because you don't know who you should tell to be at the receiving end. Asking Slashdot what is in their server log doesn't do it, because somebody could be doing a man in the middle between me and Slashdot right now. If 3 people came up to you tomorrow, each claiming to have made this post, there is fuck all you can do to determine who is telling the truth.

As a consequence, since you cannot even know who I am, you cannot possibly communicate securely with me in the future. After exchanging keys you can communicate securely with some person who may or may not be me, but you will never be able to know for sure it was that person who made this post.

Finally it is also worth mentioning here that QC, like the OTP, is limited in the amount of data you can send before meeting again to exchange entangled particles to be used for future communications. If it was not it would have an advantage over the OTP in that the OTP only lets you send so much data before you have exhausted your pad. As it happens, however, each entangled particle pair can be used only once, since any measurement destroys the entanglement.

## Re:Apples and oranges (1)

## locofungus (179280) | more than 6 years ago | (#23635753)

## Until Mrs. Tenney becomes sloppy. (1)

## Mateorabi (108522) | more than 6 years ago | (#23635229)

## Mod parent up... (1)

## argent (18001) | more than 6 years ago | (#23636351)

## ... at this level the weakest link (1)

## Fallen Andy (795676) | more than 6 years ago | (#23635379)

For a really really good look at security, try to track down the earliest black+white TV series of Mission Impossible - (almost no gadgets, lots of neat social engineering).

Andy

## Actually, Quantum Cryptography Compliments OTP (1)

## AlfredR (1095283) | more than 6 years ago | (#23636525)

Quantum cryptography promises, through quantum theory, that anyone trying to skim data from a secure channel ultimately corrupts it. So by measuring the noise level in the channel you can detect an eavesdropper.

A typical Quantum cryptography scheme requires two channels. One of the channels is a classical channel, like the internet, which is used to exchange the encrypted message. The other is a low noise quantum channel, which is capable of exchanging some kind of physical entity with information about the key encoded in its configuration. An example of such a physical entity would be a collection of polarized photons.

The rough idea is that you exchange the key over the quantum channel. If while doing that your "noise level" rises beyond a certain threshold, you abort the transmission. Otherwise the key to your OTP is now shared and you transmit your encrypted message over the classical channel.

I didn't miss your point, science isn't provably true and quantum mechanics may someday turn out to be wrong, exposing a loophole which allows for eavesdropping. But quantum cryptography isn't as much of a cryptography scheme as it is a transmission vehicle.

Still, if you want to find a flaw with quantum cryptography, you don't have to look very hard. Quantum cryptography assumes that your man in middle just wants to read data out of the channel without breaking the link. It is easily defeated if someone can make themselves into a relay.

i.e. Quantum cryptography is defeated if an eavesdropper cuts both the quantum and classical channels and inserts herself into the middle:

Sender ===>>=== Attacker ===>>== Receiver

where she pretends to be the receiver to the sender and rebroadcasts the message as if she were the sender to the receiver.

## Re:Not the most secure (1)

## blueg3 (192743) | more than 6 years ago | (#23637191)

The process of quantum "cryptography" is such that you need to ensure that nobody *now* (when you are transmitting the data) will be able to eavesdrop successfully.

## Quantum hardware DRM... (0)

## rastoboy29 (807168) | more than 6 years ago | (#23635093)

...would suck.## Re:Quantum hardware DRM... (1)

## spazdor (902907) | more than 6 years ago | (#23635423)

## Why is this practical? (3, Insightful)

## Johnno74 (252399) | more than 6 years ago | (#23635161)

Is there really anyone out there paranoid enough to need/want this besides various three-letter agencies? Maybe this is proveably secure, we think, but what is more likely - Someone finds a loophole in the very weird world of quantum mechanics that makes quantum cryptography as we know it obsolite, or someone figures out a way to find prime factors of obsenely large numbers in a reasonable time.

This article is about how it may be possible have a quantum crypto setup with a bandwidth of maybe 1024kbps by spending only $20k-$50k on one component to the system. I bet there is a lot of other components.

Compare this with a basic commodity PC, which can could encrypt 1024kbps using AES with ridiculous ease.

## Re:Why is this practical? (2, Insightful)

## mrcaseyj (902945) | more than 6 years ago | (#23635333)

## Re:Why is this practical? (1)

## Chuck Chunder (21021) | more than 6 years ago | (#23635355)

Given that we don't know it makes sense to have both.

Advances in quantum computing may make the factoring problem an easy one.

Of course the commercial applications are rather niche right now and cost is no small part of that, but how many things often start that way, including your commodity PC?

## Re:Why is this practical? (1)

## MobyDisk (75490) | more than 6 years ago | (#23639635)

## Researchers Simplify Quantum Cryptography (1)

## dgun (1056422) | more than 6 years ago | (#23636049)

## th9is FP f0r GNAA (-1, Troll)

## Anonymous Coward | more than 6 years ago | (#23636203)

## This isn't news for QKD researchers (0)

## Anonymous Coward | more than 6 years ago | (#23636285)

QKD works by making measurements of the Quantum basis that a sender sent, and generally in optical schemes you need two or four photon detectors on an optical interferometer to detect each basis. If you reduce the number of photon detectors to one, you can only detect one basis. However, the mechanisms involved allow you to still recover data and keep the key exchange secure. It isn't a fundamentally novel concept to anyone who knows the basic theory of implementing a real world QKD system.

I haven't worked on QKD in a few years, so my knowledge of the theory might be rusty, so feel free to correct me if anyone knows better.

## Thanks to this new breakthrough... (5, Funny)

## Ihmhi (1206036) | more than 6 years ago | (#23636535)

...quantum cryptography now requires 30% less cats and 46% fewer radioactive isotopes.

## 50k? no. 5k! (1)

## Briden (1003105) | more than 6 years ago | (#23638897)

sounds expensive.

except, the real article states: "Bob uses four single-photon detectors, costing approximately $5,000-$20,000 each."

still pretty expensive, but it sounds like you could have a working one of these for only 10k in detectors!