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"Unbreakable" Encryption Almost Certainly Isn't

schneier.com

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Re: "Unbreakable" Encryption Almost Certainly Isn't

#11

Post by [deleted] »

rdtsc wrote: post #3
danso wrote: post #2

> The researchers, led by Dr. Tomislav Stankovski, created an encryption mechanism that can generate a truly unlimited number of keys, which they say vastly increases the security of the communication. To do so, they took inspiration from the anatomy of the human body. Maybe this is just a problem of imprecise language and reporting, but when has the ability to generate an unlimited number of keys ever been the main…

> why do researchers brag about creating an infinite number of keys, or even "unbreakable" encryption, To generate some funding and impress gullible people? It is like unlimited energy or flying car projects.

[deleted]

Re: "Unbreakable" Encryption Almost Certainly Isn't

#12

Post by voidlogic »

andrewla wrote: post #6
LukeWalsh wrote: post #4

There's only one "unbreakable" encryption, and that's a pair of one time pads with truly random data as long as the message itself. http://www.pro-technix.com/information/crypto/pages/vernam_b...

While this may seem like a tempting statement, it is not really an answer, since "unbreakable" is not really well-defined. Clearly, "truly random" is a bit of a tough one to define. And sending the message length is a bit of an information leak itself. But even putting those aside, there's a bigger flaw. The biggest problem in this mechanism is how does the other party get their one-time pad? An upper bound on the un…

You give each party a briefcase full of 4 TB hard drives full of random numbers generated from a USB attached atomic decay device.

Now for 1,2,10 years depending on your rate of communication you can communicate using the one time pad.

>why not just send the actual message via that mechanism?

The point is you only have to exchange pads periodically, not every time you communicate.

Re: "Unbreakable" Encryption Almost Certainly Isn't

#13

Post by TeMPOraL »

andrewla wrote: post #6
LukeWalsh wrote: post #4

There's only one "unbreakable" encryption, and that's a pair of one time pads with truly random data as long as the message itself. http://www.pro-technix.com/information/crypto/pages/vernam_b...

While this may seem like a tempting statement, it is not really an answer, since "unbreakable" is not really well-defined. Clearly, "truly random" is a bit of a tough one to define. And sending the message length is a bit of an information leak itself. But even putting those aside, there's a bigger flaw. The biggest problem in this mechanism is how does the other party get their one-time pad? An upper bound on the un…

> why not just send the actual message via that mechanism?

If you can, then there's no real need for using a one-time pad. But there's a benefit that comes from a fact that exchanging the random data is a completely separate process in time and space from sending the messages. You can do it once, spending all your resources to secure it. Imagine e.g. two governments establishing a secret emergency line by generating a few terabytes of random data in one physical place and then escorting each copy in armoured trucks to proper communication factilities.

BTW. exchanging physical "XOR's" for one-time pad communication is a plot point of Vernor Vinge's "A Fire Upon the Deep".

Re: "Unbreakable" Encryption Almost Certainly Isn't

#14

Post by a1a »

voidlogic wrote: post #12
andrewla wrote: post #6

Earlier quoted context omitted.

While this may seem like a tempting statement, it is not really an answer, since "unbreakable" is not really well-defined. Clearly, "truly random" is a bit of a tough one to define. And sending the message length is a bit of an information leak itself. But even putting those aside, there's a bigger flaw. The biggest problem in this mechanism is how does the other party get their one-time pad? An upper bound on the un…

You give each party a briefcase full of 4 TB hard drives full of random numbers generated from a USB attached atomic decay device. Now for 1,2,10 years depending on your rate of communication you can communicate using the one time pad. >why not just send the actual message via that mechanism? The point is you only have to exchange pads periodically, not every time you communicate.

How do you encrypt the hard drives?

I wouldn't trust some keys that had been lying around on an unencrypted hard drive for 1,2,10 years!

Re: "Unbreakable" Encryption Almost Certainly Isn't

#15

Post by TeMPOraL »

danso wrote: post #2

> The researchers, led by Dr. Tomislav Stankovski, created an encryption mechanism that can generate a truly unlimited number of keys, which they say vastly increases the security of the communication. To do so, they took inspiration from the anatomy of the human body. Maybe this is just a problem of imprecise language and reporting, but when has the ability to generate an unlimited number of keys ever been the main…

> I'm obviously not suggesting that one-time pads have solved much of anything

Well, they did. Think about various secret channels between governments, like the Washington D.C. - Moscow line.

http://en.wikipedia.org/wiki/One-time_pad#Historical_uses

Re: "Unbreakable" Encryption Almost Certainly Isn't

#16

Post by andrewla »

cuu508 wrote: post #10
andrewla wrote: post #6

Earlier quoted context omitted.

While this may seem like a tempting statement, it is not really an answer, since "unbreakable" is not really well-defined. Clearly, "truly random" is a bit of a tough one to define. And sending the message length is a bit of an information leak itself. But even putting those aside, there's a bigger flaw. The biggest problem in this mechanism is how does the other party get their one-time pad? An upper bound on the un…

> why not just send the actual message via that mechanism? suppose you can transmit information securely only for some time. Exchange one time pads ahead of time, and use them later to communicate over insecure channel

By assumption, the only way to "transmit information securely" is by one-time pads. So...

Re: "Unbreakable" Encryption Almost Certainly Isn't

#17

Post by a1a »

hawkharris wrote: post #9

I love these two lines from Shneier's earlier article, the one he links to at the end: "The 'best cryptographers around' break a lot of ciphers. The academic literature is littered with the carcasses of ciphers broken by their analyses."

Indeed. Related advice, also from Schneier: "Anyone, from the most clueless amateur to the best cryptographer, can create an algorithm that he himself can't break. It's not even hard."

Re: "Unbreakable" Encryption Almost Certainly Isn't

#18

Post by JackGibbs »

nawitus wrote: post #8
andrewla wrote: post #6

Earlier quoted context omitted.

While this may seem like a tempting statement, it is not really an answer, since "unbreakable" is not really well-defined. Clearly, "truly random" is a bit of a tough one to define. And sending the message length is a bit of an information leak itself. But even putting those aside, there's a bigger flaw. The biggest problem in this mechanism is how does the other party get their one-time pad? An upper bound on the un…

"unbreakable" may be not well-defined, but perfect secrecy is[1]. 1. http://en.wikipedia.org/wiki/One-time_pad#Perfect_secrecy

Perfect secrecy refers to the ability to determine any information about the plaintext without decoding it. Not having it can be very useful to an attacker, but that isn't always the case. RSA, for instance, doesn't have perfect secrecy, because it leaks the Jacobi symbol (https://en.wikipedia.org/wiki/Jacobi_symbol) of the plaintext. However, that information is of limited utility, and it can be shown that determining more useful facets, for instance the parity of the plaintext, requires solving more unfeasible problems.

Re: "Unbreakable" Encryption Almost Certainly Isn't

#19

Post by andrewla »

voidlogic wrote: post #12
andrewla wrote: post #6

Earlier quoted context omitted.

While this may seem like a tempting statement, it is not really an answer, since "unbreakable" is not really well-defined. Clearly, "truly random" is a bit of a tough one to define. And sending the message length is a bit of an information leak itself. But even putting those aside, there's a bigger flaw. The biggest problem in this mechanism is how does the other party get their one-time pad? An upper bound on the un…

You give each party a briefcase full of 4 TB hard drives full of random numbers generated from a USB attached atomic decay device. Now for 1,2,10 years depending on your rate of communication you can communicate using the one time pad. >why not just send the actual message via that mechanism? The point is you only have to exchange pads periodically, not every time you communicate.

I mean, what you're saying here is that in addition to one-time-pad based cryptography, there is a "give a briefcase to the person"-based cryptographic system. In reality, I think lot more briefcase-based transfers are "cracked", as it were, than SSL sessions.

My problem is just that the proposed mechanism relies on already having an even more perfect mechanism, and thus cannot be the "only one", but is in fact strictly weaker than this other mechanism. So we have a contradiction, and we can get rid of the notion that there exists such a thing as an "unbreakable" system (or, alternatively, that it is a useful concept)

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