Author here. The thing that strikes me here is how something like Reddit Math can fall for the same kinds of 'wisdom of the crowd' things we'd typically see on Facebook.
Some people like the analogy, so the the math isn't questioned. The post hits reddit's Best Of and more people vote it up. Now it's three months since the post and you'll only notice the error if you collapse the first comment, which is full of praise for the analogy. This is despite Reddit math being a self-selected crowd with a specific interest in the topic.
Note: I originally said 'nobody noticed the error' but as @tzs points out, some users did - collapse the first reply thread and you'll see them.
Do you seriously think that anyone would implement crypto based on a reddit post?
The lack of mention of modulo multiplication is totally irrelevant for the analogy. You could also say that the box analogy is broken because Eve can take a disc cutter and open the box. Analogies don't have to be perfect duh.
I think this is one of the least useful articles I've ever seen on HN.
> Do you seriously think that anyone would implement crypto based on a reddit post?
No. I think people may have taken it as a working example of encryption. Evidently it's not.
The post in question is also specifically replying to someone asking how Bob and Alice can tell a secret, without Eve knowing. The given example does not do that.
> Are you an idiot or do you think everyone else is? This is one of the worst posts I've ever...
Not yet, I've removed the offensive parts.
But if you quote from me please quote correctly, your current comment(and the fact that you update it in every 5 minutes) is misleading.
I agree. The original Reddit post is in fact a quite good shorthand simplification and explanation of the concept.
The whole point of simplifying something to an intro level is taking out a bunch of detail so that the most important core premise becomes visible. Adding back the removed detail doesn't change the basic point of the simple explanation it refines it.
The OP appears to have fundamentally missed the point.
> Now it's three months since the post and nobody has pointed out the error, despite Reddit math being a self-selected crowd with a specific interest in the topic.
/u/GemOfEvan pointed out the error in the second highest (sorted by "Best") reply:
I think I'm missing something. Alice has a message m and a
product of primes a. She sends Bob the product ma. Bob has
the product of primes b and sends back the product mab.
Alice divides by a and sends back mb. Eve has heard the
products ma, mab, and mb. (ma)(mb)/(mab) = m, so Eve now
has the message.
Glancing through the other replies, I see at least a half dozen others also pointing out the problem, and also several explaining what it takes to make this kind of three way exchange actually work.
Reddit only reports timestamps to the month on articles this old, but all the replies I mention above say "3 months ago".
I believe the question is how can you be secure if someone is listening to both sides of the conversation and the answer is you can't in this scenario.
It's not with the box analogy: as another commenter noted, it's a well known example example you'll find in great books like Simon Singh's The Code Book."
The problem is not the analogy, the "locked-box" analogy is fine. The problem is that the math is flawed. The math is not equivalent to the analogy.
14 comments
[ 3.3 ms ] story [ 33.5 ms ] threadSome people like the analogy, so the the math isn't questioned. The post hits reddit's Best Of and more people vote it up. Now it's three months since the post and you'll only notice the error if you collapse the first comment, which is full of praise for the analogy. This is despite Reddit math being a self-selected crowd with a specific interest in the topic.
Note: I originally said 'nobody noticed the error' but as @tzs points out, some users did - collapse the first reply thread and you'll see them.
No. I think people may have taken it as a working example of encryption. Evidently it's not.
The post in question is also specifically replying to someone asking how Bob and Alice can tell a secret, without Eve knowing. The given example does not do that.
> Are you an idiot or do you think everyone else is? This is one of the worst posts I've ever...
Have you read: https://news.ycombinator.com/newsguidelines.html yet?
Not yet, I've removed the offensive parts. But if you quote from me please quote correctly, your current comment(and the fact that you update it in every 5 minutes) is misleading.
The whole point of simplifying something to an intro level is taking out a bunch of detail so that the most important core premise becomes visible. Adding back the removed detail doesn't change the basic point of the simple explanation it refines it.
The OP appears to have fundamentally missed the point.
/u/GemOfEvan pointed out the error in the second highest (sorted by "Best") reply:
Glancing through the other replies, I see at least a half dozen others also pointing out the problem, and also several explaining what it takes to make this kind of three way exchange actually work.Reddit only reports timestamps to the month on articles this old, but all the replies I mention above say "3 months ago".
Hold your mouse over the '3 months ago' and it shows the exact timestamp in a tooltip.
"There's just a small problem.
It's not with the box analogy: as another commenter noted, it's a well known example example you'll find in great books like Simon Singh's The Code Book."
The problem is not the analogy, the "locked-box" analogy is fine. The problem is that the math is flawed. The math is not equivalent to the analogy.
[1] https://en.wikipedia.org/wiki/Modular_multiplicative_inverse