explain xkcd - User contributions [en]

1935: 2018

2017-12-30T19:15:59Z

108.162.212.107: /* Explanation */

{{comic
| number = 1935
| date = December 29, 2017
| title = 2018
| image = 2018.png
| titletext = We should really start calculating it earlier, but until the end of December we're always too busy trying to figure out which day Christmas will fall on.
}}

==Explanation==
{{incomplete|Anything missing? - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

In this [[:Category:New Year|New Year comic]], [[Megan]] wonders if 2018 will be a leap year. [[Cueball]] thinks 2018 will not be a leap year, and Megan responds that she "doubts anyone knows at this point." This appears to be a jab at the complexity of the leap year system. As Cueball says, leap years occur every four years (though there are a few exceptions), adding an extra day to account for the fact that Earth takes a bit longer than 365 days to orbit the Sun. Therefore, most years that are a multiple of four are leap years. As Megan says, this is easy for odd-numbered years, since no odd numbers are divisible by four. However, for even-numbered years, it isn't always obvious.

The last panel expresses a misunderstanding of modern {{w|Cryptography|cryptography}}, which relies on the fact that it is difficult to factorize large numbers. Megan is applying this concept to the year, claiming that it is hard to determine whether or not 2018 is a multiple of four and hence is a leap year. In reality, factorization is not needed here, since we already know the factor, which is four. Megan states that if it were possible to factor large numbers with a calculator, modern cryptography would collapse. While true, it is only true for truly large numbers (hundreds of digits), and no factorization is needed in this case.

At the end of the strip, Megan hopes the answer can be {{w|Brute-force attack|brute-forced}} by February. Brute force is a method of breaking cryptography by trying every possible option until one works. This is a misdirection upon misdirection, in that even if we needed to factorize 2018 (which we don't), the simplest brute forcing algorithm would only need to try 43 numbers - from 2 to square root of 2018 (44). In cryptography, the algorithms use numbers much, much bigger than 2018 -- on the order of hundreds (or even thousands) of digits.

The title text refers to calculating which day of the week Christmas will fall on. Given that any calendar will easily tell you, this is not a difficult thing to calculate. Also it always falls on December 25th, and not like, for instance, Easter which date jumps from year to year. But nevertheless December 25th is either the 359th or the 360th (leap years) day of the year and so the day of the week could be different.

Wikipedia and many other sites reveal spoilers for this comic:
<blockquote>Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400. For example, the years 1700, 1800, and 1900 were not leap years, but the years 1600 and 2000 were.<ref>[http://aa.usno.navy.mil/faq/docs/calendars.php Introduction to Calendars]. (15 May 2013). [[United States Naval Observatory]].</ref></blockquote>

2018 is not divisible by 4, so the year is not a leap year. 2016 and 2020 are leap years. Assuming your calendar is Gregorian!

A year is roughly 365.2422 days long.

==Transcript==

:[Megan is walking.]
:Megan: I wonder if 2018 will be a leap year.

:[Now it turns out that Cueball walks behind Megan.]
:Cueball: ...it won't be, right?
:Megan: I doubt anyone knows at this point.

:[Same scene in a frame-less panel.]
:Cueball: No, it's definitely not. Leap years are divisible by 4.
:Megan: Right, and for odd numbers, that's easy.
:Megan: But 2018 is even.
:Megan: 50/50 chance.

:[Zoomed-out view with both walking in silhouette on a dark slightly curved ground.]
:Cueball: I can settle this with a calculator.
:Megan: No way. If it were easy to factor large numbers like that, modern cryptography would collapse.
:Cueball: I see.
:Megan: I just hope we manage to brute-force it by February.

==Trivia==
*Released on Friday, December 29, this is the last comic of 2017. The next scheduled comic will be on New Year's Day of 2018.

*This is the third year in a row with New Year's comics with only the year used as the title, before that there were two more comics with such titles, but those two (and thus the first three) were only released in the even years: [[998: 2012]] in 2012, [[1311: 2014]] in 2014, [[1624: 2016]] in 2016 and [[1779: 2017]] in 2017.

{{comic discussion}}

[[Category:New Year]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Cueball]]
[[Category:Comics sharing name|2017]]
[[Category:Math]]
[[Category:Time]]
[[Category:Cryptography]]

Talk:1934: Phone Security

2017-12-30T19:08:20Z

108.162.212.107:

"Detonated" ah, so this is the feature that Samsung was prototyping last year... [[User:Andyd273|Andyd273]] ([[User talk:Andyd273|talk]]) 15:39, 27 December 2017 (UTC)

:Ha! Yes, it's too bad their phones kept mistakenly registering as being stolen... stupid bugs. [[Special:Contributions/172.69.70.107|172.69.70.107]] 17:28, 27 December 2017 (UTC) Sam

:Back in the day if a hacker really hated you, you'd come back to your computer and see smoke pouring out of the CPU. I bet there's some way to detonate a phone in software by overheating the battery, but I imagine it could be different for every phone/battery combination. {{unsigned ip| 108.162.219.64}}

::Already done. http://www.zdnet.com/article/this-crypto-mining-android-malware-is-so-demanding-it-burst-a-smartphone/ [[User:Silverpie|Silverpie]] ([[User talk:Silverpie|talk]]) 23:09, 28 December 2017 (UTC)

Someone needs to make a jailbreak that does as much of this as possible, especially the ridesharing and siren 😂 [[User:PotatoGod|PotatoGod]] ([[User talk:PotatoGod|talk]]) 15:52, 27 December 2017 (UTC)

: there was or is at least one house in the U.S. that was reported, apparently inaccurately, as the location of an extraordinary number of stolen cell phones. Presumably that house would suffer all of the pranks that this phone security performs. As for payment details - someone who stole a phone may have also stolen banking cards, so, the account number that you steal back may belong to another innocent victim. It's just a joke of course, but, saying. [[Special:Contributions/162.158.111.235|162.158.111.235]] 22:02, 27 December 2017 (UTC)

Made a account just to ask this - why is the post still considered incomplete? It looks complete to me. [[User:Donutman|Donutman]] ([[User talk:Donutman|talk]]) 13:59, 28 December 2017 (UTC)

: Because I added the core explanation, but many improvements have been made since then (bullet points, bolding, transcript). Also, the siren would be insanely easy to do, as would an automated "send the GPS location to the police" among other things. [[User:Kashim|Kashim]] ([[User talk:Kashim|talk]]) 14:15, 28 December 2017 (UTC)
::I've removed the tag right now after I added that the phone would have to sense that it is stolen. There is no sensor to detect this. --[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 19:46, 28 December 2017 (UTC)
:::Bluetooth. With paired device on owner, the phone can detect if it was moved from owner. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 01:19, 29 December 2017 (UTC)
:::: No good. Firstly, no phone (that I know of) comes with such a device, which I would guess would be called a dongle. Secondly, if they did it wouldn't take long for thieves to realize they have to get the dongle, too. Thirdly, that would mean the owner could never put down their phone, like at home or at work - I've heard of a few workplaces which are high security and don't allow cell phones, so they have to be left in the car or in a locker near the entrance - unless they remember to put down the device too (which would largely defeat the purpose of such a device). And the first time they forget and the phone identified itself as stolen would be enough to convince the rightful owner that this system doesn't work. Fourthly, anything wireless must work by battery. When that battery dies, either the phone would trigger as being stolen, or it would have to detect the battery dying to not go off, in which case you're vulnerable to theft until you charge the ownership dongle. [[User:NiceGuy1|NiceGuy1]] ([[User talk:NiceGuy1|talk]]) 09:36, 29 December 2017 (UTC)
:::::All points you raised are real, but don't make it impossible. Sure, it would be bad idea to detonate or something like that when the dongle gets out of range, but it can be used to start making noise (the siren option). For the other countermeasures, the phone should detect being stolen by incorrect password being entered repeatedly. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 23:36, 29 December 2017 (UTC)
::::::Just to follow this up, for most of the countermeasures, it seems relatively clear that the phone would consider itself stolen when somebody tries to wipe it or enters the wrong password too many times. The owner would have some secret wiping procedure that performs a legitimate wipe, and when the phone is wiped using a normal procedure it considers itself stolen and engages all its countermeasures. [[Special:Contributions/108.162.212.107|108.162.212.107]] 19:08, 30 December 2017 (UTC)
: You didn't need an account to write a comment - any commenter name that's an IP address is such a guest commentor. I posted many before I created an account. :) [[User:NiceGuy1|NiceGuy1]] ([[User talk:NiceGuy1|talk]]) 09:36, 29 December 2017 (UTC)

I first thought "erase phone" meant "erase physically", but "detonate" makes that somewhat redundant. [[Special:Contributions/141.101.105.240|141.101.105.240]] 11:54, 29 December 2017 (UTC)