"Unbreakable" Encryption Almost Certainly Isn't • Hacker News Board

Re: "Unbreakable" Encryption Almost Certainly Isn't

#51

Post by 0xdeadbeefbabe » Tue, Apr 08, 2014, 4:44 PM UTC

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…

> I think lot more briefcase-based transfers are "cracked", as it were, than SSL sessions.

Lots of SSL sessions are going on right now. It only takes a vulnerability like CVE-2014-0160 to change the score by 100 or so.

Briefcases: 1 in the last day

SSL sessions: 100 in the last day

Edit: if only CVE-2014-0160 had some evocative name.

Re: "Unbreakable" Encryption Almost Certainly Isn't

#52

Post by BrandonMarc » Tue, Apr 08, 2014, 4:45 PM UTC

This axiom of Schneier's (I think it's his) can't be repeated often enough:

anyone can create a cryptosystem that he himself cannot break

It's amazing how many times a lack of knowing this axiom becomes a problem / surprise.

Re: "Unbreakable" Encryption Almost Certainly Isn't

#53

Post by klodolph » Tue, Apr 08, 2014, 5:09 PM UTC

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...

There are two known unbreakable encryption schemes, the other one is Shamir's Secret Sharing.

Re: "Unbreakable" Encryption Almost Certainly Isn't

#54

Post by IvyMike » Tue, Apr 08, 2014, 5:17 PM UTC

Xylakant wrote: post #7

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...

And even this is in practice a problem: How do you distribute and secure the pads? A lot of problems in cryptosystems stem from implementation details - think side-channel attacks, exploits, ...

"I know! I'll use a PRNG to create the one-time pad on the fly!"

Re: "Unbreakable" Encryption Almost Certainly Isn't

#55

Post by IvyMike » Tue, Apr 08, 2014, 5:18 PM UTC

mpyne wrote: post #49

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...

This was actually broken in practice once, by (you guessed it) NSA. They managed to break into part of Soviet VENONA since the demand of OTP keymat during WWII was such that someone took a shortcut and reprinted pages of random numbers. Don't ask me how Cold War-era NSA discovered that without Cray supercomputers everywhere, but even this scheme is difficult to pull off in practice.

Technically a TTP is not a OTP.

Re: "Unbreakable" Encryption Almost Certainly Isn't

#56

Post by rhth54656 » Tue, Apr 08, 2014, 5:32 PM UTC

klodolph wrote: post #53

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...

There are two known unbreakable encryption schemes, the other one is Shamir's Secret Sharing.

I believe you misrepresented that algorithm. While it is true that Shamir's Secret Sharing is unbreakable if you split the actual clear text among participants, it is not used that way. The actual use is to use SSS to encrypt and distribute the key used to encrypt the clear text.

Re: "Unbreakable" Encryption Almost Certainly Isn't

#57

Post by mpyne » Tue, Apr 08, 2014, 8:34 PM UTC

IvyMike wrote: post #55

mpyne wrote: post #49

Earlier quoted context omitted.

This was actually broken in practice once, by (you guessed it) NSA. They managed to break into part of Soviet VENONA since the demand of OTP keymat during WWII was such that someone took a shortcut and reprinted pages of random numbers. Don't ask me how Cold War-era NSA discovered that without Cray supercomputers everywhere, but even this scheme is difficult to pull off in practice.

Technically a TTP is not a OTP.

Yes, that's why I referenced in practice vs. in theory.

Re: "Unbreakable" Encryption Almost Certainly Isn't

#58

Post by klodolph » Tue, Apr 08, 2014, 8:45 PM UTC

rhth54656 wrote: post #56

klodolph wrote: post #53

Earlier quoted context omitted.

There are two known unbreakable encryption schemes, the other one is Shamir's Secret Sharing.

I believe you misrepresented that algorithm. While it is true that Shamir's Secret Sharing is unbreakable if you split the actual clear text among participants, it is not used that way. The actual use is to use SSS to encrypt and distribute the key used to encrypt the clear text.

I think you are describing a larger encryption scheme that uses SSS as a component. I am talking about SSS itself, which is unbreakable, from an information theoretic standpoint. You can use SSS to split the clear text among all participants, even if most people don't use it that way to construct larger systems.

Re: "Unbreakable" Encryption Almost Certainly Isn't

#59

Post by andrewla » Tue, Apr 08, 2014, 8:57 PM UTC

darkmighty wrote: post #47

andrewla wrote: post #36

Earlier quoted context omitted.

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…

"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." Any scheme which allows sharing arbitrary amounts of random information is less than or equally secure as an OTP (security defined per symbol) since OTP reveals no information per symbol; also, it uses the minimum amount shared…

I agree, OTP is optimal, it's just not unique, even by a very broad definition of what an OTP is. Sending a Turing machine to the other party through a secondary channel, for example, would produce an equivalently (not more) secure mechanism. Or sending a normal real number as the key, and the ciphertext is an index into the base26 expansion.

Technically, either of these could be slightly more secure, in that they need not leak the length of the plaintext. For transmitting a single "yes" vs. "no" answer, that could be a fatal attack vector for a naive OTP.

Re: "Unbreakable" Encryption Almost Certainly Isn't

#60

Post by rcxdude » Tue, Apr 08, 2014, 11:18 PM UTC

a1a wrote: post #24

"Truly unlimited number of keys" What data type would you use to store such a key? My guess is that it wouldn't be much bigger than 2048 bits after being implemented. Besides, key length is a terrible metric for measuring security.

It could be bigger. The 'keys' are just arbitrary sytems of equations, this is where 'unbounded keyspace' comes from. Any implementation would wind up being bounded by some practical constraint.

Whether this is any improvement on existing ciphers (which you can also design to have any size key you desire), is less clear, but I would bet on 'no'.