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"Unbreakable" Encryption Almost Certainly Isn't

schneier.com

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Re: "Unbreakable" Encryption Almost Certainly Isn't

#31

Post by kenjackson »

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…

When you transmit the pads may not correspond with when you want the message sent.

For example I may be able to send you a one-time pad securely today, but the message I need to tell you ("buy GM stock at 37.82") I won't know until next week -- at which point I may not be able to expediently send you the one-time pad securely.

Re: "Unbreakable" Encryption Almost Certainly Isn't

#32

Post by Loughla »

AnthonyMouse wrote: post #27
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…

> And sending the message length is a bit of an information leak itself. The known solution to this is to pad messages to some fixed length. The obvious drawback is that you have to choose the fixed length message to be as long as the longest message you may wish to transmit, which could result in having to transmit rather a lot of padding. The equivalent of this for real-time communications is to transmit continuall…

Congratulations, you just reinvinted numbers stations.

Send random data that is probably meaningless, until which point you send real data. Let everyone listen in to the gibberish for 50 years, in the end, only the person with the key knows the message.

Re: "Unbreakable" Encryption Almost Certainly Isn't

#33

Post by admax88q »

a1a wrote: post #14
voidlogic wrote: post #12

Earlier quoted context omitted.

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!

You don't get it at all.

Re: "Unbreakable" Encryption Almost Certainly Isn't

#34

Post by admax88q »

andrewla wrote: post #19
voidlogic wrote: post #12

Earlier quoted context omitted.

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 stric…

No, the notion of the unbreakable one time pad is a great notion to have around.

It is the good standard for crypto systems. Yes it's unworkable in practice but that's exactly why nobody really uses it. It is useful for teaching and making comparisons.

Re: "Unbreakable" Encryption Almost Certainly Isn't

#35

Post by voidlogic »

andrewla wrote: post #19
voidlogic wrote: post #12

Earlier quoted context omitted.

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 stric…

No, this is a a breifcase full of one time pad. If you could fit 32 4 TB hard drives full of pad in the brief case that would allow you to send 128 TB in the future securely using something like an XOR one time pad. Assuming you are just sending ASCII and compress it before sending/XORing you could send a lot more then 128 TB of ASCII.

This is pretty powerful. It means that organization which and periodically move physical assets securely can send information in a manner that is secure even if quantum computers reach their full potential.

Re: "Unbreakable" Encryption Almost Certainly Isn't

#36

Post by andrewla »

dllthomas wrote: post #21
andrewla wrote: post #16

Earlier quoted context omitted.

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

That was not the assumption. The assumption (or assertion) was that one-time pads were the only unbreakable encryption . There are ways of securing things other than encryption (most obviously physical isolation).

Ach! I let myself get drawn into a semantic argument, and it earned me my first downvotes!

My only point was that talking about one-time-pads as "unbreakable" encryption is not a useful discussion, since "unbreakable" and "encryption" need to be better defined.

If we expand the definition of "encryption scheme" sufficiently to allow transmission of secrets outside of cryptographic channels, then OTP is not even close to the only unbreakable system.

Only by explicitly defining attack vectors can we really get a good framework for reasoning about cryptography, and even then we know that we can prove an encryption technique is bad. For "goodness", all we can do is increase our confidence, until the day the confidence drops to 0.

Anyway, with this last salvo, I'll retreat from this conversation; it's pretty clear to me that my inane ramblings about semantics are as annoying to the community here as they are to me when other people make them.

Re: "Unbreakable" Encryption Almost Certainly Isn't

#37

Post by voidlogic »

admax88q wrote: post #34
andrewla wrote: post #19

Earlier quoted context omitted.

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 stric…

No, the notion of the unbreakable one time pad is a great notion to have around. It is the good standard for crypto systems. Yes it's unworkable in practice but that's exactly why nobody really uses it. It is useful for teaching and making comparisons.

Governments use it all the time. (Men with handcuffed briefcases and armed guards..)

Before you send your submarine to sea for example, you can provide them with many gigabytes of one time pad. They can then use this for their most secret communication.

Re: "Unbreakable" Encryption Almost Certainly Isn't

#38

Post by voidlogic »

omh wrote: post #30
a1a wrote: post #14

Earlier quoted context omitted.

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!

If I was using one-time-pads I'd probably be using them because I didn't trust encryption, so "unencrypted" wouldn't matter here. In real-world implementations I think the security is probably based around a large number of men with guns.

Exactly, men with guns secure the one time pad. The data sent using that pad is secure.

Nit: I would consider one time pad to be a method of encryption.

Re: "Unbreakable" Encryption Almost Certainly Isn't

#40

Post by dghf »

TeMPOraL wrote: post #15
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

I read a novel by a former SAS soldier about a former SAS soldier who's sent on deniable operations by the British government, and who uses what is clearly a one-time pad to communicate with his handlers. The detailed description of the precise method used, the fact that the term "one-time pad" is never used, and the narrator's apparent lack of understanding of how exactly it works (encryption/decryption is done via modulo-10 addition/subtraction, which the narrator derisively refers to as "spook maths") suggest that the author himself, or a contact of his in the same circles, has used a very similar system for real.
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