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

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

#11

Post by chacham15 » Tue, May 21, 2013, 3:17 AM UTC

doktrin wrote: post #3

I feel like I'm missing something. Isn't this still vulnerable to "electronic" intrusion, since the light-slab-cipher has to presumably be read into some type of memory somewhere, somehow?

Yes, they assume that the sending/receiving machines arent themselves compromised. That case, however, doesnt have a solution as of yet (that I know of). The point is that any machine intercepting the transmission of the message has no way of possibly decoding it period. It absolutely requires the key to be decoded.

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

#12

Post by chacham15 » Tue, May 21, 2013, 3:20 AM UTC

jere wrote: post #5

>That looks to be a significant improvement over any kind of cryptography that stores keys electronically and is therefore vulnerable to an electronic attack that can copy digital information perfectly. Hmmm... so is paper?

Well, you cant send paper privately in milliseconds across the country. But yes, the meeting to create the key limits the possible receivers as well as a connivance hassle.

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

#13

Post by chacham15 » Tue, May 21, 2013, 3:23 AM UTC

mc-lovin wrote: post #7

Can someone explain this to me? I read the article but it didn't make sense. The physical object as I understand it provides a source of random data, with the property that it is fast to do a single lookup (shine an arbitrary light pattern on it), but slow to copy the whole data. This means that an attacker who steals the object, but doesn't know which lookups will be done, won't be able to copy all the data. Now my…

I understood that the lookups are standard, i.e. anyone can do them. The problem is that shining light through glass creates heat which can change the structure of the glass if you do it too often/quickly, hence the time limiting factor. Naturally, this would constrain the intended recipient as well. It is the outcome of these lookups that form the secret key.

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

#14

Post by Groxx » Tue, May 21, 2013, 3:29 AM UTC

As far as I can tell, it's just a reasonably large on-demand (until it overheats) source of randomness. All the other OTP principles hold, the glass-generated random bits are the only new things. And you can still "electronically copy" it - viruses are great at executing code, such as dumping all the random data such a thing can generate (they even say it would only take 24 hours, and less to upload).

I suspect it's not even very good randomness. Long dark / bright lines from deeper scratches at either end, skewed randomness due to the atomic structure of glass (though glass is probably a reasonably good natural source, since it's not crystalline), that sort of thing happens when you're dealing with physical (hard, static) structures. And this thing has to be very reproducible or you can't decrypt your message, so we're not talking extracting randomness from a warm cup of tea.

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

#15

Post by ReidZB » Tue, May 21, 2013, 3:48 AM UTC

mc-lovin wrote: post #7

Can someone explain this to me? I read the article but it didn't make sense. The physical object as I understand it provides a source of random data, with the property that it is fast to do a single lookup (shine an arbitrary light pattern on it), but slow to copy the whole data. This means that an attacker who steals the object, but doesn't know which lookups will be done, won't be able to copy all the data. Now my…

The original paper [1] is much clearer about the actual algorithm. The below is pretty much pulled straight from it, although I simplify it slightly (by assuming one pattern, etc.)

First, Alice and Bob decide on a pattern P. Then they each compute a key K(A) and K(B) using the pattern P by shining P through their slab. Then, they publicly publish P and K(A) ⊕ K(B). (Apologies for the lack of good mathematical notation, but HN is not a great medium for such.)

Because P, K(A), and K(B) are all random, the attacker learns no useful information from these two published items.

Now, for Alice to encrypt a message m, she computes K(A) ⊕ m and sends it to Bob. Once Bob gets it, he uses the public pattern P to recreate K(B). Then he uses the publicly published K(A) ⊕ K(B) to compute:

K(B) ⊕ [K(A) ⊕ K(B)] ⊕ (K(A) ⊕ m)

which is in fact m. At any time, the Eve can only know P (useless since she doesn't have either slab) and K(A) ⊕ K(B), which is not enough to recover the key or message.

[1]: http://arxiv.org/abs/1305.3886

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

#16

Post by ovoxo » Tue, May 21, 2013, 3:48 AM UTC

Can someone help me understand something - Manufacturing the "glass" in order to create at least 2 identical copies will require some blueprint. I would assume that this blueprint would be stored in some database or communicated to various parties in some fashion. Couldn't hackers just get their hands on this somehow in order to reproduce the glass without having to actually physically steal the glass?

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

#17

Post by rdl » Tue, May 21, 2013, 3:49 AM UTC

There's been a lot of "physically unclonable function" work, which IMO is a lot more useful for DRM and anti-counterfeiting than for encryption.

The big weakness with OTPs is inadvertent key reuse, not someone stealing the key wholesale.

Even with quantum computing, conventional OTPs are fine, provided keys aren't reused (or lost). OTOH there are plenty of other more efficient symmetric and asymmetric systems which are still fine under quantum computing, too. (it's really not much of an issue for conventional symmetric cryptography; yes, most common public key systems in use today fall to quantum cryptography, but their are known/viable systems which would be fine)

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

#18

Post by ReidZB » Tue, May 21, 2013, 3:50 AM UTC

ovoxo wrote: post #16

Can someone help me understand something - Manufacturing the "glass" in order to create at least 2 identical copies will require some blueprint. I would assume that this blueprint would be stored in some database or communicated to various parties in some fashion. Couldn't hackers just get their hands on this somehow in order to reproduce the glass without having to actually physically steal the glass?

The two slabs are actually different. See my explanation of the algorithm downthread: https://news.ycombinator.com/item?id=5741793

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

#19

Post by mc-lovin » Tue, May 21, 2013, 3:52 AM UTC

ReidZB wrote: post #15

mc-lovin wrote: post #7

Can someone explain this to me? I read the article but it didn't make sense. The physical object as I understand it provides a source of random data, with the property that it is fast to do a single lookup (shine an arbitrary light pattern on it), but slow to copy the whole data. This means that an attacker who steals the object, but doesn't know which lookups will be done, won't be able to copy all the data. Now my…

The original paper [1] is much clearer about the actual algorithm. The below is pretty much pulled straight from it, although I simplify it slightly (by assuming one pattern, etc.) First, Alice and Bob decide on a pattern P. Then they each compute a key K(A) and K(B) using the pattern P by shining P through their slab. Then, they publicly publish P and K(A) ⊕ K(B). (Apologies for the lack of good mathematical notatio…

Thanks, that's what I thought but I'm glad you confirmed it and put it in their notation.

So here is my issue:

Eve knows P, so she can steal the object and hence compute K(B).

The difficulty in "copying" the object is only significant when Eve does not know P.

But that same difficulty would apply if K(A) and K(B) were random numbers that Alice and Bob generated when they met.

Or is the point that Alice and Bob generate K(A) + K(B) for a lot of values of P, and then randomly select the ones to use when sending a message? That doesn't seem to be what the authors intended, although it would now be secure against stealing the object for a short amount of time.

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

#20

Post by ovoxo » Tue, May 21, 2013, 4:05 AM UTC

ReidZB wrote: post #18

ovoxo wrote: post #16

Can someone help me understand something - Manufacturing the "glass" in order to create at least 2 identical copies will require some blueprint. I would assume that this blueprint would be stored in some database or communicated to various parties in some fashion. Couldn't hackers just get their hands on this somehow in order to reproduce the glass without having to actually physically steal the glass?

The two slabs are actually different. See my explanation of the algorithm downthread: https://news.ycombinator.com/item?id=5741793

Ahh ok - great explanation btw.

I'm still curious how this glass is produced. It seems to me that you would be introducing many more potential intrusion points by using physical encryptors since many more parties (people, databases, and systems) will be aware of the details in order to produce the appropriate slab. Having said that, the same thing would apply for any other physical encryptor that would have to be manufactured.