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From: unruh on 18 May 2010 15:31
On 2010-05-18, Maaartin <grajcar1(a)seznam.cz> wrote:
> Isn't the whole quantum cryptography simply too impractical, at least
> at the moment? It gives us some proven security based on physical
> theories which are believed to be right. Conventional cryptography
> gives us some proven security based on cryptographic theories which

No, it does NOT give us proven security. That is its problem. It is
secure as long as certain things are believed to be too hard to do, but
it is known that all of the used cyphers are "weak" and not secure
against an opponent with arbitrary resources. Quantum crypto is secure
against an opponent with arbitrary resources.

> are believed to be right. While the physical laws are more solid, the
> implementation of quantum transmissions is much more complicated, thus
> giving more opportunities for errors. Most cryptographic failures are
> based on weak implementations as opposed to weak ciphers; only in
> cases of working with limited resources the cipher failed (e.g., WEP
> disaster).

Q comp can be set up to be secure even against (some) implimenation
problems. That is why people are excited about it.


>
> Or am I talking nonsense? I do not argue against the research, I only
> think that the state of the art in quantum cryptography is not
> advanced enough.

For what?

From: Mok-Kong Shen on 18 May 2010 15:41
unruh wrote:
> Maaartin wrote:
>> Isn't the whole quantum cryptography simply too impractical, at least
>> at the moment? It gives us some proven security based on physical
>> theories which are believed to be right. Conventional cryptography
>> gives us some proven security based on cryptographic theories which
>
> No, it does NOT give us proven security. That is its problem. It is
> secure as long as certain things are believed to be too hard to do, but
> it is known that all of the used cyphers are "weak" and not secure
> against an opponent with arbitrary resources. Quantum crypto is secure
> against an opponent with arbitrary resources.

Maybe a dumb question: What do you say to (genuine) OTP?

M. K. Shen
From: unruh on 18 May 2010 16:40
On 2010-05-18, Mok-Kong Shen <mok-kong.shen(a)t-online.de> wrote:
> unruh wrote:
>> Maaartin wrote:
>>> Isn't the whole quantum cryptography simply too impractical, at least
>>> at the moment? It gives us some proven security based on physical
>>> theories which are believed to be right. Conventional cryptography
>>> gives us some proven security based on cryptographic theories which
>>
>> No, it does NOT give us proven security. That is its problem. It is
>> secure as long as certain things are believed to be too hard to do, but
>> it is known that all of the used cyphers are "weak" and not secure
>> against an opponent with arbitrary resources. Quantum crypto is secure
>> against an opponent with arbitrary resources.
>
> Maybe a dumb question: What do you say to (genuine) OTP?

It is proven secure. The key distributions problems make it far too hard
to impliment. (The key distribution make the key vulnerable to theft, and copying)

But it was not OTP that he was refering to (at least I hope not)
Note that the problem that QCrypto solves is precisely the key
distribution problem of the OTP. Thereafter to actaully transmit the
message conventional crypto is used ( perhaps even OTP)

>
> M. K. Shen
From: Mok-Kong Shen on 18 May 2010 17:16
unruh wrote:
> Mok-Kong Shen wrote:

>> Maybe a dumb question: What do you say to (genuine) OTP?
>
> It is proven secure. The key distributions problems make it far too hard
> to impliment. (The key distribution make the key vulnerable to theft, and copying)
>
> But it was not OTP that he was refering to (at least I hope not)
> Note that the problem that QCrypto solves is precisely the key
> distribution problem of the OTP. Thereafter to actaully transmit the
> message conventional crypto is used ( perhaps even OTP)

On the other hand I am afraid that there is one aspect that is shared
by OTP and quantum crypto, namely they are both "theoretically"
extremely fine but have huge difficulties in "practice", which I suppose
is the tenor of OP's first post.

M. K. Shen



From: Maaartin on 18 May 2010 18:27
On May 18, 9:31 pm, unruh <un...(a)wormhole.physics.ubc.ca> wrote:
> On 2010-05-18, Maaartin <grajc...(a)seznam.cz> wrote:
>
> > Isn't the whole quantum cryptography simply too impractical, at least
> > at the moment? It gives us some proven security based on physical
> > theories which are believed to be right. Conventional cryptography
> > gives us some proven security based on cryptographic theories which
>
> No, it does NOT give us proven security. That is its problem. It is
> secure as long as certain things are believed to be too hard to do, but
> it is known that all of the used cyphers are "weak" and not secure
> against an opponent with arbitrary resources.

Sure, but there's provably no opponent with arbitrary resources in a
limited universe. We may assume opponents with extreme computing
power, but it's possible to find an upper limit and IMHO it's possible
to make the problem hard enough for anybody given the state of the art
of attacks. I agree that it's impossible under the assumption of an
opponent using yet unknown attacks.

> Quantum crypto is secure
> against an opponent with arbitrary resources.

OK.

> > Or am I talking nonsense? I do not argue against the research, I only
> > think that the state of the art in quantum cryptography is not
> > advanced enough.
>
> For what?

For practical and economical use - I know it's been already used, but
weren't there alternatives? Was it a pure commercial application or
was it (partly) a scientific experiment? My knowledge here is very
limited, so bear with me.
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