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Serious Flaw Emerges In Quantum Cryptography

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Re: Serious Flaw Emerges In Quantum Cryptography

#11

Post by ThomPete »

VikingCoder wrote: post #9
tjoff wrote: post #7

Earlier quoted context omitted.

You can't prove that you can trust the carrier. And with trust I not only mean that the carrier has good intentions but also that the carrier is physically unable to do any mistakes. Also you can't prove that someone doesn't sniff the traffic when you copy it to your second DROBO and you can't prove that none of the drives have been copied afterwards. Not saying that your approach isn't "secure enough" (I'd guess tha…

Thanks for the reply! > You can't prove that you can trust the carrier. I said that I physically carry DROBO two to my intended recipient. I can trust myself. > Also you can't prove that someone doesn't sniff the traffic when you copy it to your second DROBO and you can't prove that none of the drives have been copied afterwards. There is no such thing as secure communication. Copying data from one DROBO to another D…

Even if you carry it yourself then you don't necessarily know if it was used right?

Re: Serious Flaw Emerges In Quantum Cryptography

#12

Post by cgray4 »

benmmurphy wrote: post #8

i don't understand how it is not susceptible to MITM attacks. how do you know you know the thing at the other end is really who you want to talk to without using some kind of preshared key? maybe an eavesdropper can't view the conversation between you and the other end but that doesn't matter if someone can easily pretend to be the other end.

As far as I understand it (which isn't too far), quantum bits are physical things. So only the person who has the qubits can see the key exchange. As long as the qubits are physically safe in the hands of the person you want to talk to (admittedly a big if), there can't be a MITM attack.

Re: Serious Flaw Emerges In Quantum Cryptography

#13

Post by aidenn0 »

tjoff wrote: post #5
srl wrote: post #2

If I'm understanding this correctly, the "serious flaw" recently uncovered is that if the manufacturer of the crypto devices is malicious, the crypto devices can be made to be insecure. Despite the fact that this same "serious flaw" exists with classical cryptography devices, only worse (since the quantum attack doesn't reveal plaintext A until B is sent). (Disclosure: haven't bothered to read the arXicle.)

Despite the fact that this same "serious flaw" exists with classical cryptography devices, only worse (since the quantum attack doesn't reveal plaintext A until B is sent). How would you do this with classical cryptography? Isn't the point about this particular flaw that it is pretty much undetectable (other than inspecting the hardware itself (which is outside the scope of the article that treats it as a black box))…

"How would you do this with classical cryptography?"

Nearly every classical cryptography device uses a source of entropy; if you break that intentionally then you have a side-channel.

Re: Serious Flaw Emerges In Quantum Cryptography

#14

Post by mindslight »

VikingCoder wrote: post #6

Okay, here I go on a tangent: If I buy two 5-bay DROBOs, 10 2 TB HDs, and a hardware random number generator, I could make a multi-TB One Time Pad, and copy it onto the second DROBO. I keep DROBO one, and physically carry DROBO two to my intended recipient. What are the problems with this? It's cheap. It's as secure as any communication could possibly be. It provides for a whole lot of communication, with relatively…

I know it's right up there with the "Caesar Cipher" on the cuteness sale, but the "One Time Pad" shouldn't even be considered cryptography. The only thing it does is shift the secret in time, against a passive attacker.

Re: Serious Flaw Emerges In Quantum Cryptography

#15

Post by aidenn0 »

VikingCoder wrote: post #6

Okay, here I go on a tangent: If I buy two 5-bay DROBOs, 10 2 TB HDs, and a hardware random number generator, I could make a multi-TB One Time Pad, and copy it onto the second DROBO. I keep DROBO one, and physically carry DROBO two to my intended recipient. What are the problems with this? It's cheap. It's as secure as any communication could possibly be. It provides for a whole lot of communication, with relatively…

1) Your random number generator could be broken

2) I can flip bits in your message without you detecting it.

3) I can send random messages and get your receiver out of sync with you.

Re: Serious Flaw Emerges In Quantum Cryptography

#16

Post by Groxx »

>"In short, the problem is that an adversary can program devices to store data in one protocol and leak it in subsequent protocols, in ways that are hard or impossible to counter if the devices are reused," say Barrett and co.

You mean, if you store the encryption key and later reveal it to outside sources, your secure communication is no longer secure? SHOCK AND AWE.

It's complete fluff that has nothing to do with quantum cryptography, just the intrinsic chain-of-trust of whatever hardware you're using. If something you're using is untrustworthy, the whole chain is - this is not a new discovery.

Re: Serious Flaw Emerges In Quantum Cryptography

#17

Post by tptacek »

VikingCoder wrote: post #6

Okay, here I go on a tangent: If I buy two 5-bay DROBOs, 10 2 TB HDs, and a hardware random number generator, I could make a multi-TB One Time Pad, and copy it onto the second DROBO. I keep DROBO one, and physically carry DROBO two to my intended recipient. What are the problems with this? It's cheap. It's as secure as any communication could possibly be. It provides for a whole lot of communication, with relatively…

The problem with this is that it is unlikely to be in practical terms better than using two slips of paper to write down a 256 bit random number and using that to establish a long-lived AES-256-CTR session.

(This is without getting into the fact that a single keystream is not a secure message exchange protocol, and that conventional cryptography has well-tested ways of linking confidentiality secrets to integrity secrets and of marshalling and canonicalizing messages; I'm just answering your question on its own terms).

None of this has much to do with QC, by the way; as I understand it, QC replaces conventional number-theoretic public key crypto, not block and stream ciphers.

Re: Serious Flaw Emerges In Quantum Cryptography

#18

Post by VikingCoder »

ThomPete wrote: post #11
VikingCoder wrote: post #9

Earlier quoted context omitted.

Thanks for the reply! > You can't prove that you can trust the carrier. I said that I physically carry DROBO two to my intended recipient. I can trust myself. > Also you can't prove that someone doesn't sniff the traffic when you copy it to your second DROBO and you can't prove that none of the drives have been copied afterwards. There is no such thing as secure communication. Copying data from one DROBO to another D…

Even if you carry it yourself then you don't necessarily know if it was used right?

...true of all cryptography systems.

Meaning: my proposed system is no more or less vulnerable than any other, in this regard.

Re: Serious Flaw Emerges In Quantum Cryptography

#19

Post by greeneggs »

benmmurphy wrote: post #8

i don't understand how it is not susceptible to MITM attacks. how do you know you know the thing at the other end is really who you want to talk to without using some kind of preshared key? maybe an eavesdropper can't view the conversation between you and the other end but that doesn't matter if someone can easily pretend to be the other end.

Both standard quantum key distribution (QKD) and device-independent quantum key distribution schemes assume that the two parties share an authenticated classical channel. Without authentication, of course you cannot prevent man-in-the-middle attacks.

Authentication can be established using a shared secret (which is why purists sometimes refer to QKD as a key expansion protocol). Or, it can be established using signatures and certificate authorities. It is worth pointing out that man-in-the-middle (MITM) attacks must be made online; if you break a signature scheme a year after the QKD protocol finishes, it does not compromise the key.

Re: Serious Flaw Emerges In Quantum Cryptography

#20

Post by VikingCoder »

aidenn0 wrote: post #15
VikingCoder wrote: post #6

Okay, here I go on a tangent: If I buy two 5-bay DROBOs, 10 2 TB HDs, and a hardware random number generator, I could make a multi-TB One Time Pad, and copy it onto the second DROBO. I keep DROBO one, and physically carry DROBO two to my intended recipient. What are the problems with this? It's cheap. It's as secure as any communication could possibly be. It provides for a whole lot of communication, with relatively…

1) Your random number generator could be broken 2) I can flip bits in your message without you detecting it. 3) I can send random messages and get your receiver out of sync with you.

1) True. Buy a few of them, and XOR them all together.

2) I can always have a Message Digest of my message included.

3) If the Message Digest doesn't match, the message will not be accepted as valid. The receiver will not be out of sync.

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