I think this is a shockingly good example of how smart people get security questions utterly wrong. The right analogy when it comes to security has to involve some type of adversary, not just random, unmotivated natural phenomena -- as long as we're using aircraft analogies, it's not so much "a meteorite might randomly hit my plane in flight" as "there's angry and armed people shooting at my plane with armour-piercing ammunition".

Indeed, in the real world, putting hundreds of kilograms of armour on aircraft isn't the absurd/childish idea Linus seems to think it is:

https://en.wikipedia.org/wiki/Fairchild_Republic_A-10_Thunde...

It seems like a straightforward, almost painfully obvious definition in retrospect now, after having it articulated to me. I think education on security manners is poor and should be a standard topic.

What's interesting here is that, just 5 years ago, the 2017 cost of this very attack (the Stevens attack) was estimated at 2^18.4 = $350k [0]. The collision announced today cost about $100k. Perhaps even less. [1]

Cloud computing is cheaper today than many expected it to be, and it seems like we're only now entering the era of fierce competition. Who knows what the next decade will bring. If your modeled attacker cost is within an order of magnitude or two of the danger zone, beware. Better to have many orders of magnitude of headroom.

Along these lines, I really like what cperciva did with attacker cost modeling in his scrypt paper. See the table on page 14 [2]. I wish more security choices were presented this way, with estimated attacker costs. Taking that even further, I wish the numbers were updated dynamically against present day hardware & compute costs. Maybe even with trendline projections. It's difficult to make good security choices without knowing costs.

[0] https://www.schneier.com/blog/archives/2012/10/when_will_we_...

[1] https://sites.google.com/site/itstheshappening/

[2] https://www.tarsnap.com/scrypt/scrypt.pdf

And it hunts tanks.

The plane was built for survivability. It can withstand an engine being shot off (why the engines are external on "pods"). The cockpit is (I think) surrounded by a 2 inch titanium tub.

I'm not sure the JSF, i.e. F-35 will be capable of taking over this role, as is intended.

The radioactivity is unrelated to its use as bullets, which relies on its high density, but it is radioactive.

If one of those is lingering, I wouldn't even fight if I was the enemy.

It might not be able to kill a modern main battle tank, but I bet spraying it with rounds like that would fuck it up pretty seriously.

Another story that I've heard is that a B-1 flying at operational altitude (200 ft above ground level, mach 2) was often as effective as dropping munitions.

That very topic is being discussed right now on the Aviation Stack Exchange: http://aviation.stackexchange.com/questions/35771/is-it-corr...

People tend to really underestimate how much harder it is to go faster once you reach 0.90 or so, especially at low altitudes.

But the if a small meteorite (only a few grams) were traveling that slow, 1.5 inches of titanium would do quite a bit.

"At some point, usually between 15 to 20 km (9-12 miles or 48,000-63,000 feet) altitude, the meteoroid remnants will decelerate to the point that the ablation process stops, and visible light is no longer generated. This occurs at a speed of about 2-4 km/sec (4500-9000 mph). From that point onward, the stones will rapidly decelerate further until they are falling at their terminal velocity, which will generally be somewhere between 0.1 and 0.2 km/sec (200 mph to 400 mph). Moving at these rapid speeds, the meteorite(s) will be essentially invisible during this final “dark flight” portion of their fall."

0. http://www.amsmeteors.org/fireballs/faqf/

just btw, 25 km/s is almost 100.000 km/h.

https://en.wikipedia.org/wiki/Impact_event#Airbursts

One they get big enough, they slow down from ludicrously fast to still ludicrously fast. The smallest impactor shown in that table enters at 17 km/s, loses 90% of its energy traversing the atmosphere and smacks the ground at nearly 5km/s. You'll probably want to take your titanium armour and stand somewhere else.

"A METHOD OF ESTIMATING PLANE VULNERABILITY BASED ON DAMAGE OF SURVIVORS" BY ABRAHAM WALD (1943) : http://www4.ncsu.edu/~swu6/documents/A_Reprint_Plane_Vulnera...

  (1) P(crash | section hit)

Let's directly apply Bayes' rule:

  (2) P(crash | section hit) = P(section hit | crash) * P(crash) / P(section hit)

  (3) P(section hit) = P(section hit | crash) * P(crash) + P(section hit | no crash) * P(no crash)

Another point in this method's favor is if crashed aircraft frames are too damaged to permit us to identify which sections were damaged. In that case, we can still estimate (1) just by replacing all the P(section hit | crash) terms with a uniform term.

This analysis can be further expanded to the actual amount of damage each section took in a as well. The more damage a section took on surviving aircraft, the less protection it needs.

It's not like a rifle bullet.

> it could be incredible bad luck that caused that good-looking patch to be mistakenly matching a dangerous object

So this is a shockingly good example of how quotes taken out of context are pretty useless in a discussion.

Using analogies is okay when you try to explain a difficult idea to somebody who wants to learn about your subject. Using analogies is not okay when you want to make a solid argument, when you want to convince somebody whose stance is very different from yours.

It's to communicate an idea to another person in a way that can also convey subtleties, and not just the literal words being conveyed.

In this case, he was trying to convey the idea that the risk is so small and so remote that it really isn't worth spending a lot of time on.

You understood the point, I understood the point, and everyone else understood the point. Which means the analogy was successful.

So please, stop trying to pull the conversation on some tangent so you expound on why smart people should spend more time on the perfect analogy that you approve of.

The purpose of an analogy is to simplify something that's too hard to understand for the person you try to convey your idea to. Sometimes analogies are appropriate, e.g. when you teach something. When you want to convince somebody whose opinion is very different from yours, analogies aren't appropriate. They sound condescending: "because you are not smart enough to understand the real rationale behind my opinion, here is an oversimplified argument based on analogies I made just for you". The question is, did Torvalds have any real argument back then? Maybe he fell back to using analogies for the lack of any real argument.

> In this case, he was trying to convey the idea that the risk is so small and so remote that it really isn't worth spending a lot of time on.

To convey the idea that the risk is very small, one needs to have a proof. Real proofs shouldn't involve analogies. They should use facts and logic.

An analogy applies a principle to a common setting without loss of specificity. Specifically the dedicated adversary is lost in this abstraction, so it's a bad analogy.

That's just the nature of an analogy, but that doesn't make it useless or fair to attack the speaker for using an analogy.

And now we're debating on what does and doesn't qualify as an analogy.

And to be quite honest abstracting ideas is core to problem solving, and I think it's a bit disingenuous to say that anyone misunderstood what Linus was getting at there.

Sure. But don't confuse abstractions with analogies.

Here is a good proof about both the integers and rational numbers. Every integer and rational is a real number (abstraction). When you add any 2 real numbers, you get the same result regardless of their order (fact). So it must be true that, when you add any 2 integers, you get the same result regardless of their order (correct conclusion #1). It also must be true that, when you add any 2 rationals, you get the same result too (correct conclusion #2).

Here is a bad proof about the integers and rational numbers. Both the integers and rationals are very similar: you can add them, subtract them and so on (analogy). Between every 2 rational numbers there is another rational number (fact). So it must be true that between every 2 integers there is another integer (wrong conclusion).

Anyone who doesn't understand why the risk was so small doesn't belong in the conversation.

Can you even imagine where our medical field would be if we expected surgeons to talk amongst themselves as if they were speaking to the general public?

It is absolutely acceptable for the speaker to make assumptions about the listeners knowledge, and that doesn't reflect poorly on the speaker.

> The purpose of an analogy is to simplify something that's too hard to understand for the person you try to convey your idea to.

It's to convey an idea. That's it, anything you add to that is your own bias at work.

Linus was trying to get across the scale of just how small the risk was.

The Git devs are not heart surgeons, software development is not a medical field. Again, you are using an analogy to "prove" your point. Can you, please, use a real argument?

>> The purpose of an analogy is to simplify something that's too hard to understand for the person you try to convey your idea to.

> It's to convey an idea. That's it, anything you add to that is your own bias at work.

Do you disagree that using an analogy is oversimplification? If you don't, then that part about "to simplify a complex idea" in my statement should absolutely stay. If you do disagree, then please show why and how an analogy doesn't oversimplify a complex idea.

When someone uses an analogy they're not trying to prove anything, they're trying to get you to see things from a specific perspective, or they're trying to communicate an idea.

You can still walk away from the analogy and disagree with them, but you should have a better understanding of their perspective or their argument.

> Do you disagree that using an analogy is oversimplification?

I think your entire approach to analogies is unnecessarily combative. You view an analogy as someone trying to prove something rather than trying to communicate their position better (or just an idea in general).

And your approach is to point out that the analogy isn't perfect, and therefore you've "disproved" the analogy.

Only analogies are, by their very nature, imperfect. When an analogy is perfect it ceases to be an analogy and becomes the thing being discussed.

It should automatically be understood that there are the analogy isn't perfect and anyone can find flaws in it. That doesn't mean it isn't an effective way to communicate.

Sure, if he's saying he is powerless against higher powers. But if he's trying to make a quantitative assertion, a qualitative analogy is not the right tool.

This was his point, and it's still true. Generating a specific SHA-1 hash is still not feasible.

Not really. It's not a preimage attack. They spent several hundred dollars to find two random byte strings with the same SHA1 hash. There's still no way to SHA1-collide a specific byte string instead of random junk.

Why is this quoted in support of an argument that Linus used to come across as a lunatic in online correspondence ?

This seems to me like an entirely reasonable way to make it very, very difficult to ever attack, because an attacker would have to be able to generate collisions for both of your hash functions.

(I'm not a crypto expert -- maybe you are, if so and my above comment is totally wrong, can you explain how it's wrong?)

But of course, now is not then. And I think zkms' metaphor "there's angry and armed people shooting at my plane with armour-piercing ammunition" is apt here. The threat is much more sizable now, and so the cost vs. benefit analysis has changed.

Incidentally, one of the requirements of the SHA-3 competition was that it not be related to previous hashes. So while there are no demonstratable attacks against SHA-2, we nonetheless have "two ...hashes, and that they are based on totally different principles."

[1] https://news.ycombinator.com/item?id=13715146

[2] https://www.iacr.org/archive/crypto2004/31520306/multicollis...

What all the commenters here doing a hatchet-job on Torvalds are missing is that he's saying "show me the money"/"perfect is the enemy of good". The hatchet-jobbers are too busy doing the usual tittering over his language to actually absorb the point.

Also, "more secure" doesn't necessarily mean "more complex", or "slower". Blake2b for instance is as fast as md5 and has a simple RAX (xor, rot, add) core from Chacha20.

There's also important concern about SHA-512 (which has led to SHA-3 and other options), but I'm not sure it can be put in the same category; at least all of the best attacks today are significantly reduced-round.

https://en.wikipedia.org/wiki/SHA-2#Cryptanalysis_and_valida...

By contrast, Wang's original attack (which we had more than 10 years ago) achieved a 2¹¹ speedup for collisions against full SHA-1 and her second attack later the same year achieved 2¹⁷ speedup.

Evidently the speedup for the final version of Stevens's attack (which worked) was also around 2¹⁷. By contrast, a Moore's law improvement over 10 years would only be expected to make computers around 2⁶ times faster! (At the risk of mixed or mangled metaphors, we might say that mathematical insight during the time period you mention has been about 2¹¹ times more useful for attacking SHA-1 than computer power increases.)

Edit: someone else linked to Valerie Aurora's chart, which I'd forgotten about, which gives a synopsis of the historical status of the most popular hashes. On that chart, SHA-1 from 2005 was one category worse ("Weakened") than SHA-512 is today ("Minor weakness").

http://valerieaurora.org/hash.html

"I have no evidence of SHA-1 being broken which is evidence that SHA-1 can't be broken"