One-Time Pad reinvented to make electronic copying impossible • Hacker News Board

Re: One-Time Pad reinvented to make electronic copying impossible

#31

Post by PeterisP » Tue, May 21, 2013, 7:56 AM UTC

Well, in practice, public/private key encryption with large keys does achieve the same security, as does meeting in person (as required here) and simply exchanging a 100gb flash with a random OTP.

What this method does is makes it harder to attack if the Bob's key/OTP is physically stolen. ALthough keys embedded on secure chip-cards cheaply and commonly available now are just as secure - the authors apparently claim that the keys can be read off the glass blocks in less than 24 hours; and extracting a long key off a chip-card (even if it's just pin-protected with permanent blocking for x mistakes) would be a bigger pain, you have to physicially scan the chip with extremely expensive gear for that.

What this method doesn't do, is "make electronic copying impossible" or facilitate DRM, since Bob or anyone who compromises Bob's computers can freely copy and distribute the data right after the decryption.

Re: One-Time Pad reinvented to make electronic copying impossible

#32

Post by _red » Tue, May 21, 2013, 9:01 AM UTC

rosser wrote: post #4

Lanzaa wrote: post #2

This is a very interesting way of solving the key distribution problem. It forces attackers to capture both the digital part of the key and the physical.

This doesn't solve the key distribution problem at all: To start off, both Alice and Bob must have their own slabs of diffusing glass and must physically meet to create a key for encoding a message later. Like any other OTP system, key distribution — ensuring that the parties who wish to communicate securely have a shared secret (or secrets in the case of OTP; the whole point of OTP is that a key is only used once) —…

Correct, I can't see the practical use of this.

If Alice and Bob must have a secure method to jointly compute K(A) ⊕ K(B), then why wouldn't then use that same method to just exchange the data?

Re: One-Time Pad reinvented to make electronic copying impossible

#33

Post by dsr_ » Tue, May 21, 2013, 9:44 AM UTC

_red wrote: post #32

rosser wrote: post #4

Earlier quoted context omitted.

This doesn't solve the key distribution problem at all: To start off, both Alice and Bob must have their own slabs of diffusing glass and must physically meet to create a key for encoding a message later. Like any other OTP system, key distribution — ensuring that the parties who wish to communicate securely have a shared secret (or secrets in the case of OTP; the whole point of OTP is that a key is only used once) —…

Correct, I can't see the practical use of this. If Alice and Bob must have a secure method to jointly compute K(A) ⊕ K(B), then why wouldn't then use that same method to just exchange the data?

At the time of their key-exchange meeting, they don't know what messages they will want to exchange later.

Re: One-Time Pad reinvented to make electronic copying impossible

#34

Post by Tycho » Tue, May 21, 2013, 12:02 PM UTC

When I read articles like this, I imagine scenarios involving some United Earth Government sending vessels deep into space with one time pads which would protect us from evesdropping from advanced hostile civilizations with vast computing/cracking power. I guess it would kind of suck if your glass got broke and then you couldn't decode any more messages from Earth.

Re: One-Time Pad reinvented to make electronic copying impossible

#35

Post by ReidZB » Tue, May 21, 2013, 3:26 PM UTC

mc-lovin wrote: post #25

ReidZB wrote: post #21

Earlier quoted context omitted.

Interesting point. I'm not sure what prevents Eve from simply computing K(B) from P if she has stolen Bob's slab. Maybe I have misinterpreted something? The actual paper does describe generating n different patterns and then randomly selecting one of them to encrypt the message, but the index of the one that is randomly selected is sent with the encrypted message so that Bob can use it to look up the appropriate patt…

>But one of the other requirements set forth in the paper is that if the slab is stolen, Eve must not be able to send or receive messages. I'm not sure how that is fulfilled here. If a "full" message involved both sides randomly picking a P, then this could still be satisfied. But it doesn't seem to live up to my hopes for security: all it really guarantees is that the probability of Eve decrypting an intercepted mes…

When I woke up this morning (and was in a better state of mind), I realized the supplements may have been on the arXiv page but not included in the paper. I was correct. Here [1] is the supplement paper, which I find more useful than the actual paper itself.

It appears I was correct about the stolen CPUF leading to decryption of previous messages; in supplement G, at the bottom of (2), the authors state:

"Finally, it is worth noting that with a stolen device and access to the public dictionary, an attacker Eve may be able to quickly decrypt any of Alice and Bob’s previous communication that she may have saved(since Alice and Bob publically share which SLM patterns they use each round). For this reason, it is highly beneficial for Alice and Bob to utilize a second layer of encryption to ensure that any eavesdropper cannot determine these previously shared patterns, as discussed next."

They also discuss other security properties of the scheme in supplements G and H, which are both excellent.

[1]: http://arxiv.org/src/1305.3886v1/anc/CPUF_Supplementary_Mate...