
Death Note: L, Anonymity and Eluding Entropy (2017) - tosh
https://www.gwern.net/Death-Note-Anonymity
======
arugulum
I would frame things a little differently. Light makes a lot of mistakes
because the Death note is incredibly powerful and there would be almost no
reasonable way for L to catch Light without Light making obvious mistakes (and
would also make for a boring story). Undoubtedly, the biggest mistake Light
makes is revealing the existence of the Death Note, and all the rules therein,
which not only gives L (almost) all the information he needs, but also traps
him from any subsequent activity.

Without knowing the rules of the Death Note, I don't think L could have done
anything (besides outright abducting/murdering Light) to stop Light, even if
he is 100% sure Light is "responsible".

That said, I feel like a much simpler solution than what's proposed at the end
of the essay is:

1\. Gather up the names you want to write over the course of a week. 2\. Wait
another week, then write it at a specific point of time of the week. 3\. Keep
to that schedule.

The names need to be as public and as well known as possible such that it
would be impossible to trace the flow of information. (Remember, the goal is
fear, not specificity.) Keeping to that schedule means you will never leak
more information thereafter.

~~~
michaelscott
I agree with this completely; Light makes up for what I would say is an
inferior deductive ability by using a supernatural item with rules that defy
ordinary logic and reason (L catches on early that such a tool must exist with
his TV announcement stunt, but he can't possibly know the ruleset of such an
item).

The only way Near and Mello end up overcoming this advantage is by: (1) Mello
obtaining a Death Note of his own, allowing him to ascertain the real ruleset,
and (2) Near not being directly involved in Light's life the way L was, and
there not leaking any extra information about himself until the finale. That
last bit is especially critical considering L was taken out precisely because
he was physically present and therefore had his real name observed by
Shinigami eyes.

I think the most under-utilized ability of the Death Note in the series is the
ability to specify manner of death. Light uses this on occasion, but he
could've have made many criminal deaths seem accidental or suicidal in
addition to staggering their occurrences in time in order to throw L off from
the very beginning.

~~~
arugulum
>I think the most under-utilized ability of the Death Note in the series is
the ability to specify manner of death.

Absolutely. This ability is so significant that it completely overshadows the
ability to kill people. If anything, the deaths should be treated as an
unfortunate byproduct of being able to control people for 23 days in a row.

~~~
chacha2
There were limits to this ability though. All behaviour had to be in
character.

~~~
arugulum
Agreed, but there is still so much you can do. You can make dictators
liberalize their countries. You can make billionaires donate away their
wealth. And so on.

------
Malic
This is somewhat related to a thought experiment of mine.

Suppose you had a means of transmitting information back in time - a one-node
network that effectively could email to itself with a timestamp (in the past)
being the message's "recipient."

Suppose such a thing existed in the world today. Assume the individuals in
possession of such a thing were very intelligent, very careful and very
guarded about its use.

Could you still detect that such a thing existed by observing real-world
events - stock market changes, tech innovations, amazing coincidences and the
like? What evidence would you look for?

~~~
c22
If you possessed such a device then errors in your "predictions" would be
indicative of another party using a similar device. As such, I assume multiple
parties would soon discover each other, engage in an incomprehensibly complex
time-battle, and there would suddenly ( _instantaneously_ in all patched
timelines) be only one such party.

Furthermore, I imagine it would be very easy for such a party to accidently
blunder into a situation where they lose control of the time-messaging device,
erasing all evidence of its own existence and leaving the timeline
perturbation-free until such "time" as reverse time travel is rediscovered.

~~~
alasano
As a fan of time travel movies, I'd watch this.

~~~
ecnahc515
You may like the anime Steins;Gate then. The plot is based on the idea of
sending a small amount of information back in time and changing the sender's
present, and then finds that another organization has been using this and is
trying to control the world with the power.

------
cyphar
Very interesting article, my only real contention is on the point made in
Mistake 4:

> You can see it was a gamble by considering if Light had been outside Kanto;
> since he would not see it live, he would not have reacted, and all L would
> learn is that his suspect was in that other 2/3 of the population, for a
> gain of only ~0.3 bits.

My understanding of L's plan (based on what he said in the broadcast) was that
he intended to do several live broadcasts, one in each region, until he was
caught. Lind L. Taylor was a death row criminal being offered a deal to
survive, and would've gone along with doing several broadcasts. Additionally,
even if they didn't do it live and simply recorded it there's no way that
Light would've known it wasn't live and he would've acted in the same manner
(and since Lind was in L's custody, L would've known if he died even if Light
didn't).

At the time Death Note was written, mass internet communication wasn't as
prevalent and so you wouldn't expect people to find out about events like the
broadcast for at least a few hours (long enough to do broadcasts in each
region). L probably hoped that Kira was in a less populated city since it
would cut down on more bits of entropy (and I'd argue it would've been a
better idea to start broadcasting to smaller cities first -- since it's more
likely an event like this in a big city would be quickly broadcast to the rest
of Japan).

~~~
Liquid_Fire
From a pure efficiency point of view, if you are bisecting like this it is
best to divide in halves, which gives you 1 bit of information each time
regardless of the outcome.

Of course, this assumes you can continue to apply the same method many times,
which probably doesn't apply to this case, as you can only fool Light with a
similar method a limited number of times (possibly once only). In that case
you probably want to do it more fine-grained than 1/3 so that you get more
bits of information once you get to the first (and therefore last) successful
attempt.

------
arugulum
As a fun mental exercise, I've been wondering if the Death note could've been
used to solve difficult computational problems. As far as I know, the
following abides by Death Note rules, in particular we know that the Death
Note is able to "manipulate" luck. Assume Bob Robert is an amateur
mathematician, so this is something he would reasonably do and guess.

"Bob Robert. Writes down a number X>=82,589,933 where 2^X-1 is a prime number
as his guess of the next largest known prime number, and it is indeed correct.
Then dies of a heart attack."

~~~
cbau
If I remember correctly, it has to be something that the person was actually
capable of, otherwise the person just dies.

~~~
arugulum
The person is capable of writing down X, it's a handful of digits. Moreover it
is not unreasonable for an amateur mathematician to do so.

The fact that they entirely lucky that the series of digits indeed satisfies
the mathematical condition we want is incidental but I believe abides by Death
Note rules.

~~~
danShumway
I think "capable" also takes into account knowledge they have.

It's been a while since I watched Death Note, but isn't this brought up as a
reason why Kira can't do, "writes down L's real name, then dies of a heart
attack."?

It would be theoretically possible for someone to be lucky enough to guess L's
real name, but apparently the note has a bullcrap detector or something where
it eventually just says, "no, they wouldn't _really_ know to do that."

~~~
arugulum
Well we know the reason why Light says he can't do that is that "the person
wouldn't know the name". But you're right in actuality that would allow for
"person guesses the name, and is correct". And I think that _is_ a loophole.

Let me put this another way. I think the following would be considered a valid
Death Note command.

"Person flips a coin 100 times in a row, and gets heads every time".

Now how is that different from

"Person runs an RNG digit generator 100 times in a row, and gets 9s every
time".

Then

"Person runs an RNG digit generator 100 times in a row, the 100 digit number
is exactly divisible by 123456".

Then

"Person runs an RNG digit generator 100 times in a row, 2^x-1 of that number
is prime".

And if this is all iffy, let me propose an alternative. Let's assume (I'm not
100% sure of this) that we can _verify_ large prime within 23 days. Heck,
build a data center to do this if we have to.

"Person runs RNG to generate x such that 2^x-1 is prime. Uses machine and
verifies that it is indeed prime. Dies of joy."

You can similarly use this to crack hashes, etc.

~~~
hobofan
The Death Note doesn't give the target any magic abilities, that the
previously didn't have.

> "Person flips a coin 100 times in a row, and gets heads every time".

I'm pretty sure this would be interpreted as "The person has to flip coins
until they have a 100 streak of only heads". This will obviously take a really
long time, and the person might be driven insane before that. Similar things
go for your other examples.

In a comment further up you wrote:

> in particular we know that the Death Note is able to "manipulate" luck

I don't recall that specifically. Even then, I would guess that this has it's
bounds. I also have the feeling (not backed up by lore, but I think it would
fit in the world), that bigger manipulations would take more energy from the
respective shinigami, so while a shinigami might be able to manipulate luck
enough to make someone win the lottery, finding prime numbers would be too
draining.

~~~
arugulum
>I'm pretty sure this would be interpreted as "The person has to flip coins
until they have a 100 streak of only heads".

I disagree. For example, Light has people die of getting run over a by truck.
But the Death note does not interpret this is as "person repeatedly crosses
the street until they get run over by a truck". Instead, events are
(reasonably) manipulated such that a truck runs them over. Similarly, the
coins would be manipulated to have 100 heads in a row.

>I also have the feeling (not backed up by lore, but I think it would fit in
the world), that bigger manipulations would take more energy from the
respective shinigami, so while a shinigami might be able to manipulate luck
enough to make someone win the lottery, finding prime numbers would be too
draining.

I wouldn't be surprised if this is true, but hey, what's a couple of Shinigami
to save us some compute!

~~~
danShumway
My impression is that the Death Note would only manipulate luck to a certain
degree -- ie, if the odds of even occurring are greater than 1/x, just make it
happen. That would allow you to get hit by a truck crossing the street, but
not allow you to win a coin flip 100 times (7.8886091e-31 odds). You'd
probably have to experiment to figure out what the threshold was.

That being said... let's assume you're right. If the death note can manipulate
odds to an arbitrary degree, you're thinking _way_ too small right now. It
would be much more efficient to write:

"X opens a laptop text editor, closes their eyes, and hits keys randomly. They
open their eyes and discover they have accidentally written an algorithm for
quickly factoring large numbers. They copy and paste this algorithm into an
encrypted email to light.iskira@gmail.com, then die by jumping in front of a
bus."

If X dies of a heart attack, you know your instructions didn't take and
there's no algorithm for quickly factoring large numbers -- the problem was
impossible. But then you can start modifying your query for, "an easy strategy
for keeping cubits stable", or whatever you want to follow up with.

If I have a fast-track to get at almost any (possible) invention I can think
of, I'm not going to waste my time factoring large numbers!

~~~
arugulum
>If the death note can manipulate odds to an arbitrary degree, you're thinking
way too small right now.

Right, what I feel might be the case is that the targeted output needs to at
least be verifiable (hence see my second proposal). An argument could be made
that unless the person has a way of verifying their action, there is no way to
ensure that the desired outcome is achieved, so the instruction is invalid.
(Separately, at least in your written example, it is possible for the person
to be mistaken about the validity of their method!)

On the other hands, actions that are (machine) verifiable fall right within
the scope of the Death Note (insofar as the verification instruments are also
reliable, and verification happens within 23 days). I emphasize machine
verifiable because the Death Note has various rules concerning other people,
which I won't wade into. If "X starts his car and his car engine explodes" is
valid, then so should "X keys a random string of inputs into a machine,
machine returns True, then X dies."

So no we've limited the scope of DN-solvable problems to 23-day machine-
verifiable problems. Now we just need to know what set of problems are 23-day
machine-verifiable...

~~~
danShumway
> it is possible for the person to be mistaken about the validity of their
> method

That's a good point.

> are 23-day machine-verifiable

Here's a followup question. Can a person be part of the machine?

For example, I might rephrase my earlier entry to be:

"X closes their eyes and types random keys, such that they form an algorithm
for quickly factoring large primes. They email that algorithm to
light.iskira@gmail.com and receive a confirmation that their algorithm is
sound. At which point, they become so excited that they run into the street
and are hit by a bus and killed."

My worry with that is that if there is some kind of force behind the death
note, it might decide to just manipulate _me_ instead of the person writing
the algorithm. I don't want an evil genie scenario where I just accidentally
write "yes, it works", instead of "no, it doesn't."

By extension, if we have a 23-day machine-verifiable problem, am I allowed to
specify that the machine is not glitching or producing errors? In some cases,
that might be more likely than finding the correct answer. Shinagami picking
the most likely scenario that technically fits the criteria might be an
effective way for them to reduce some abuse of the system.

------
saagarjha
> Worse, the deaths are non-random in other ways—they tend to occur at
> particular times! Graphed, daily patterns jump out.

I actually ran this kind of analysis on my use of Hacker News a couple of
months back. It turns out that the patterns mentioned only really work if you
have something that resembles a normal sleep schedule, which I clearly do not:

    
    
      12 AM  *********
      1 AM   ***********
      2 AM   *********
      3 AM   *******
      4 AM   *****
      5 AM   ****
      6 AM   ***
      7 AM   **
      8 AM   ****
      9 AM   *****
      10 AM  *********
      11 AM  ***********
      12 PM  ***********
      1 PM   ****************
      2 PM   *************
      3 PM   ***************
      4 PM   ************
      5 PM   **************
      6 PM   ***********
      7 PM   *******
      8 PM   **********
      9 PM   *********
      10 PM  ********
      11 PM  *******
    

(Each * corresponds to 25 comments; to my knowledge the vast majority of
comments were made from PST)

~~~
lonelappde
As in the OP, it's pretty obvious when you are sleeping.

~~~
saagarjha
Sure, but would you believe that I'm now sleeping ~10 PM-7 AM? I'm not
convinced there's enough information there to narrow down my location to
anything smaller than a hemisphere.

------
joe_the_user
The ability to kill anyone one chose would be a far more terrifying weapon if
used to instill fear. If someone used to this ability to kill individuals who
didn't fit their agenda but kept anonymity about their goals, whatever changed
they wished would only happen fairly slowly and haphazardly - those replacing
the dead wouldn't have that much chance to produce different policies.

Also, even a bunch of seemingly random deaths with implications would likely
produce terrifying fits of paranoia and retribution in the populace - remember
humans can't not-see patterns in the thing they focus on, so a death-weapon
would change the world this way - not sure if that what your psychopath
wanted.

If an actor could kill "anyone nominated to head party X" then things would
get ugly but even more, "do these things and you're immune" notes could
certainly get people moving, especially if these were seemingly benevolent.
"Random company heads die 'till CO2 production declines X amount" for example.

~~~
Arnavion
The Death Note could control what the victim did before their death. So Global
Warming Kira could definitely have those random company heads die next to a
piece of paper with "the deaths will continue until CO2 declines" written on
it.

~~~
whatshisface
Then you could write, "Before their death, the CEO of Gas Inc. will invent
nuclear fusion, spread it to every market, and then live a long and happy
life."

~~~
the8472
There are rules that would prevent that (they can only do things within their
means, 1 month time limit).

What could work is an investment in such technologies, public announcements
and then disappearing, maybe falling off a yacht or such a thing.

~~~
zaarn
"Scientist X, working on Fusion, discovers method that advances research by
decades, then dies of happiness and a caffeine overdose"

------
needle0
Characters in fiction regularly behave sub-optimally even if they're set up as
geniuses, for the most mundane meta reason: It's a work of entertainment, and
the plot wouldn't get interesting otherwise! We should always be very aware
that any fiction, even ones that attempt speculative simulations, is always
shackled by the need to keep being entertaining and interesting -- there are
craptons of concepts and possibilities that _can_ occur or _will_ become
deeply relevant to humanity but hardly ever gets explored in fiction because
they're boring to read or write about.

~~~
lorenzq
I really enjoyed Harry Potter and the Methods of rationality. I understand not
everyone would like such an intelligent main character though.

------
teej
One thing the author seemingly didn't address - the overlap in entropy between
the different mistakes. For example, Mistake 2 in timing leaked 6 bits, but
those same 6 bits got leaked as a part of Mistake 4 in using confidential
police information. Mistake 4 on its own is possibly the worst, but if you
consider what L already knows, it's only 5 incremental bits lost.

Despite that, loved the article.

~~~
mjevans
The two mistakes corroborated each other and the second was only possible to
observe based on the refining characteristic intrinsic to the earlier mistake.
Additionally the second wouldn't have necessarily invalidated the first six
bits, though it would strengthen refinement along a different path.

------
d4mi3n
This was well cited with a lot of fun media references. The author makes a few
interesting points on rationale for randomization, calling known unknowns and
confounding factors as something one could plan for and avoid.

Anybody know of other writers that do research and writing in this style? I
quite enjoyed it.

~~~
inetsee
Gwern Branwen has a large body of work on a broad range of topics. You could
go to the top of his web page [https://www.gwern.net/](https://www.gwern.net/)
, pick a topic that interests you, and start reading.

~~~
fireattack
I admire his site, but for some reason, I found his content very hard to
digest. I can read if someone links to any particular article, but browsing
through the index is very overwhelming to me.

I don't know if it's just the sheer amount of content that feels intimidating
or anything else (like reading long paragraphs of sans-serif fonts on screen).

------
MordecaiMaxwell
This website really impressed me - a lot of interesting stuff to read, for
sure.

~~~
SomaticPirate
Agree wholeheartedly. It's rare to find a website today that is so abjectly
different than the rest of the web.

~~~
ip26
Abject =~ despicable

~~~
gwern
I find 'abject' an amusing adjective to apply. It makes one imagine the author
writhing on the ground in despair after loading a standard website, and
despondent - _o tempora! o mores!_ \- resolving to be different.

(Not entirely wrong, as it happens.)

------
lawn
If it's true that privacy is dead, how come Satoshi is still unknown?

~~~
s_y_n_t_a_x
He/they may be known to some. [https://medium.com/cryptomuse/how-the-nsa-
caught-satoshi-nak...](https://medium.com/cryptomuse/how-the-nsa-caught-
satoshi-nakamoto-868affcef595)

~~~
wyxuan
Stylometry only works too an extent with helping to identify what's what. I
could just stylometry to show that this document was written by a professional
screenwriter, but it writing style isn't unique enough to identify one person
out of billions. Gwern has an excellent post about this.

~~~
zawerf
I remember a really impressive demo where someone found all the alt accounts
of a HN user using stylometry:
[https://news.ycombinator.com/item?id=17944484](https://news.ycombinator.com/item?id=17944484)
The account didn't have that many comments on it (maybe ~1000 karma)

He also claims to have used the same algorithm for identifying company
insiders for trades (see parent comment in that thread for context).

I don't think he was bullshitting even though his tool isn't public because he
has a different NLP project that works reasonably well
([https://hnprofile.com/](https://hnprofile.com/) which can find users based
on their interests).

------
hyperion2010
This is up there for one of the most thorough proofs that God (if she exists,
for most meanings of exists) cannot interact with the universe in ways that
contravene statistical mechanics.

------
jacobush
Someone on HN linked to a list of the best anime - and I can't find it now,
because I foolishly thought I would remember the name of the website.

Anyone know what I am talking about? The "winning entry" was, I think some
kind of pretty abstract anime story. If Death Note was on the list at all (the
list may have been compiled before Death Note was aired), it was not on the
top of the list. The list was written by a single author and it had extensive
long-form style commentary.

~~~
jhpriestley
I think you're a few bits short of specifying a website here

------
PaulHoule
Death Note is great...

[https://www.youtube.com/watch?v=d5HT8HoiAHg](https://www.youtube.com/watch?v=d5HT8HoiAHg)

Death Note is based on the "keep your enemies close" that turns up a lot in
Japanese Culture. For instance, more than once in Sailor Moon the bad guys
wind up embedded with the good guys, and the same thing happens in Tales of
Symphonia. Thus it is almost necessary for the plot for Light to move in with
L.

------
La-ang
Light's mistakes are part of the plot, not an error in it. He eventually loses
as the Shinigami predicts that he will be the one writing his name on his
Death Note. L also sacrifices himself knowing that he should close down on
Kira and Near eventually puts an end to it. Yet my issue was with Light
killing using the bag of chips with the TV inside, what kinda TV could fit
there and render visible information with low light in a dark surveilled room?

~~~
rtkwe
Ah but if he hadn't done that we wouldn't have gotten the classic "I'll take a
chip.... AND I'LL EAT IT!" line which really couldn't be more critical to
Death Note.

On a more serious note I don't think this is trying to say the show is wrong
for having these mistakes just that the character could have done better and
thinking about how is fun and allows you to examine just how much information
leaks from seemingly benign sources.

------
Legogris
This might be the nerdiest article I've seen.

Also a great illustration why CoinJoin is not a complete transaction privacy
solution for Bitcoin.

