explain xkcd - User contributions [en]

1808: Hacking

2017-03-08T15:10:00Z

Rhettinger: Possible references to ShellShock or to compiler injection attacks

{{comic
| number = 1808
| date = March 8, 2017
| title = Hacking
| image = hacking.png
| titletext = The dump also contains a list of millions of prime factors, a 0-day Tamagotchi exploit, and a technique for getting gcc and bash to execute arbitrary code.
}}

==Explanation==
{{incomplete|The main joke from the caption, that this is not dramatic revelation, like Cueball seems to think (sarcasm?) is not mentioned yet.}}
While publishing email addresses on websites, people often add space between parts of the email. For example, john.doe@example.org may be written as john dot doe at example dot org. This is to prevent the page scraping bots from harvesting email addresses, which may in turn be sold as address lists for email marketers.

In this comic, [[Ponytail]] tells [[Cueball]] that there is a tool which can delete such spaces. Such a tool can fix the space and most likely convert the words "dot" and "at" into their respective symbols. This will overcome the problems faced by such harvesting tools, and make these email addresses more prone to receive spam. Cueball appears shocked to hear this news, but given the caption below this may be sarcasm. A program written to remove a space is of course not very complicated, and believing you e-mail to be safe from harvesting by writing a space in to the address is very naive.

This comic is referencing a leak by {{w|WikiLeaks}} that compromises thousands of hacking exploits (thus the title) and programs from the CIA on the day before this comic was released, March 7 2017. (See for instance this article: [https://www.wired.com/2017/03/wikileaks-cia-hacks-dump/ WikiLeaks Just Dumped a Mega-Trove of CIA Hacking Secrets]). Many of the tools that were in the leak were similar to publicly available tools, or not entirely unexpected, with several coming from sites such as StackOverflow and reddit.

The title text references more interesting-sounding, but useless, parts of the dump:
* Millions of prime factors: {{w|Prime factorization}} can be used to break a {{w|RSA (cryptosystem)|RSA cipher}} by turning a large number into prime factors: this is a very hard problem, which is what makes the cipher secure. A list with many prime factors, however, is easy to generate, and the chance of one of the numbers on the list being a prime factor for the number used in the RSA cipher is very slim.
* A 0-day exploit for {{w|Tamagotchi}}: a 0-day exploit is an exploit of which the manufacturer is not (yet) aware. While modern Tamagotchi do have some network functionality, this is likely useless because Tamagotchi are very low-end devices that do not contain microphones or cameras. (There is some truly excellent work on this at [http://natashenka.ca/ Natalie's page] which is a must-read, and as this comic was published on International Women's day, today is a fine day to start if you have not already).
* A way to get {{w|GNU_Compiler_Collection|gcc}} and {{w|Bash_(Unix_shell)|bash}} to execute arbitrary code: gcc is a {{w|compiler}}, so preparing arbitrary code is its main purpose, and bash is a Unix shell, so executing {{w|Shell script|arbitrary code}} is one of its functions. Then again, this could be a reference to {{w|Shellshock_(software_bug)|ShellShock}}, a major vulnerability which allowed the unintentional execution of arbitrary attacker code. Likewise, it could be referring to a [http://wiki.c2.com/?TheKenThompsonHack compiler injection attack] which allows a compiler to inject backdoors via the binary executables in a toolchain and without leaving a trace in the source code being compiled or the compiler itself.

==Transcript==
:[Ponytail is writing on her laptop at her desk while Cueball looks over her shoulder.]
:Ponytail: You know how sometimes people put a space in their email address to make it harder to harvest?
:Cueball: Yeah?
:Ponytail: ''They have a tool that can delete the space!''
:Cueball: Oh my god.

:[Caption below the panel:]
:Less-dramatic revelations from the CIA hacking dump

==Trivia==
*This is the second comic in a row about how computers can be misused and also the second in a row where Cueball is with Ponytail rather than [[Megan]].
**This setup with Ponytail at the computer and Cueball behind has been used several times for instance in [[1513: Code Quality]], part of the [[:Category:Code Quality|Code Quality]] series.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Cueball]]
[[Category:Computers]]
[[Category:Cryptography]]

1806: Borrow Your Laptop

2017-03-04T04:44:49Z

Rhettinger: /* Explanation */ Add a citation for Emacs users swapping the Control and CapsLock keys.

{{comic
| number = 1806
| date = March 3, 2017
| title = Borrow Your Laptop
| image = borrow_your_laptop.png
| titletext = If used with software that could keep up, a scroll wheel mapped to send a stream of 'undo' and 'redo' events could be kind of cool.
}}

==Explanation==
{{incomplete|Randall is NOT Cueball (see discussion)! Everything is senseless -- who changes the keyboard layout without changing the keyboard itself? Typing blindly is just a guess but not shown in the comic.}}
[[White Hat]] asks to borrow [[Cueball|Cueball's]] laptop to load something. Cueball (a stand-in for [[Randall]]) permits this, but immediately begins rattling off a list of very unusual key- and mouse-bindings that he has applied to the device. In the caption, [[Randall]] states that he tends to continually re-configure computers that he owns in weird ways, eventually rendering it unusable (or at least unpleasant to use) for everyone else.

Like many other computer users Randall likes to customize his PC. Of the three items in Cueball's list of customizations only one seems like a real and relevant setting. That is the first, which is that hitting both shift keys simultaneously will change the keyboard back to QWERTY. The {{w|QWERTY}} keyboard is the standard in the US (as well as some other places using the roman alphabet). It has been a [[:Category:Dvorak|recurrent theme]] for Randall to refer to the {{w|Dvorak Simplified Keyboard|Dvorak}} keyboard layout, and, although he doesn't say so, it seems safe to assume that this is the current setting, as it is one of the most common QWERTY competitors, and has been repeatedly mentioned in the comic. Supporters claim that typing speed is faster on a Dvorak keyboard, although this is still contentious, and this is a reason Randall often makes jokes about it. (See more details [[:Category:Dvorak|here]]). The laptop has most likely a standard QWERTY keyboard, but if Cueball can type blindly in Dvorak he would not be troubled by the fact that the keys typed a different letter than what is on the keyboard's key. This relation was also the pun in the recent comic [[1787: Voice Commands]]. The same problem would arise if the computer is set to another language than what the keyboard was meant for.

The next point on the list makes less sense, as Cueball has changed his keyboard layout so that caps lock acts as the {{w|control key}}, but then also moved {{w|capslock}} so that is activated when hitting {{w|spacebar}}. Swapping capslock and control is actually a common thing to do in the world of Unix or for users of [https://www.emacswiki.org/emacs/MovingTheCtrlKey the Emacs editor]. Since the "Caps Lock" key (immediately to the left of the "A" in a traditional layout) is much easier to reach for a touch typist than the more out-of-the-way "Ctrl", even though the latter is often used more frequently, especially by programmers. On the other hand, moving the capslock function to the space bar is quite impractical, as the spacebar is the largest key, and one which would likely not normally be used for anything other than spaces, making accidental application of caps lock more likely. Most people do not use capslock enough to justify giving it the largest key on the board, as whichever key Randall now chooses for space will be harder to reach, making him more likely to make mistakes in typing, such as pressing a letter key, or tab, or alt, for example, when trying to type a space. What's worse, he doesn't tell White Hat where he has hidden the space bar, although it could of course be the two ctrl keys, which would at least give him two possible (but much smaller) spacebars to use, one on either side of the keyboard.

People have more reason to change their keyboard layouts on laptops, due to the reduced keyboard, which can leave vital keys out, especially if it was bought in a foreign keyboard layout. Rather than change the keyboard layout all the time in order to access keys which are not accessible in one of the layouts, one can take advantage of text substitution and keyboard remapping programs to set shortcuts for keys they use often.

Finally he goes out on a limb with an impossible setting, which is that his scroll wheel moves through time instead of through "space" (as in up and down on the screen), but only when using {{w|Touchpad#Operation_and_function|two-finger scroll}}, which often used on {{w|Touchpad|touchpads}}/track pads for laptops as a gesture for scrolling. Time travel is also a [[:Category:Time travel|recurrent theme]] on xkcd. Quite likely Randall has chosen this example because of the inconsistency of some systems interpreting two-finger scrolling opposite of others (two-finger scrolling in the up-direction on some systems moves the content up, on others down.) This is often configurable, but is further complicated by the fact that "inverted scrolling" is used in opposite meanings on different systems.

Finally it becomes clear these three settings are not the only important points, as Cueball's list continues with at least one other point which is not in the comic.

In the title text it is revealed that Cueball actually did not mean moving in real time, in the sense of time travel, but rather that the two-finger scroll would act as an {{w|undo|undo/redo}} button. This would represent a form of metaphorical "time travel" by using "undo" to recover a past state of the currently open file and "redo" to go to a later (but no later than the present) point in time. Scrolling rapidly up and down would let the user rapidly build and unbuild whatever they were making, potentially a cool visual (see also [https://youtu.be/ZIqWPohGmmM time lapse art]). In the title text Randall says that he would actually find such a feature cool, but that he doesn't think that the programs on his laptop could keep up if his scroll wheel was mapped to send a stream of undo/redo commands to them as he used it. It would also interfere with the normal use of the scroll key for scrolling or zooming.

==Transcript==
:[White Hat walks toward Cueball's desk pointing at his laptop while looking back at Cueball standing behind him.]
:White Hat: Can I load it up on your laptop?
:Cueball: Sure!
:Cueball: Oh, just hit both shift keys to change over to QWERTY.
:Cueball: Caps lock is control. And spacebar is capslock.
:Cueball: And two-finger scroll moves through time instead of space.
:Cueball: And–

:[Caption below the panel:]
:Once I've used a computer for a while no one else will ever use it again.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring White Hat]]
[[Category:Computers]]
[[Category:Time travel]]
[[Category:Time]]

1798: Box Plot

2017-02-14T01:23:33Z

Rhettinger: /* Explanation */ Entasis

{{comic
| number = 1798
| date = February 13, 2017
| title = Box Plot
| image = box_plot.png
| titletext = You have to be careful doing this. Sometimes, when you push the whisker down, dynamite explodes.
}}

==Explanation==
{{incomplete|Are dynamite detonators like this still in use? Better explanation of box plot etc? Inflation of data, is that a real concept, which Randall mocks? Ref to other comics with data manipulation.}}

This comic shows a {{w|Box plot|box plots}} in the first panel, hence the title.

In {{w|descriptive statistics}}, a box plot is a convenient way of graphically depicting groups of numerical data through their {{w|quartiles}}. The second quartile is the median and it is not indicated in this comic, as it should be a line through the box, see the {{w|Quartile#Definitions|definitions of quartiles}}. But the top and bottom of the box is the first and third quartile, which splits the lowest/highest 25% off data of from the highest/lowest 75%, respectively.

Box plots may also have lines extending vertically from the boxes (whiskers) indicating variability outside the upper and lower quartiles, hence the terms box-and-whisker plot. These can be used to indicate the {{w|interquartile range}}, a measure of {{w|statistical dispersion}}. These have been included on the three boxes in the plot.

The joke in the comic arises, because it turns out that the box plot is actually three real world objects and [[Cueball]] walks into the plot in the second panel, climbs up on the lower first box and on to the highest middle box. When the boxes are depicted in the orientation shown, the boxes can look like they are pumps, where the middle part, the box, can be pumped up. And Cueball does just that in the fourth panel, by pushing the top whisker down and when he leaves in the fifth and last panel, this box stays inflated, with the whisker visibly lower than in the first three panels, although higher than when he pushed it down in the fourth panel. (Inflating things, that cannot be inflated, was also the joke in [[1395: Power Cord]]. But as opposed to inflating the meaning of data, which many researchers sadly do in the real world, what [[Beret Guy]] does in that comic, is strictly [[:Category:Strange powers of Beret Guy|supernatural]].)

It could be said that the "data" in this comic was "inflated" and thus Cueball has been trying to show a smaller interquartile range than there actually is, thus inflating the possible conclusions that could be drawn from the data.

It is also possible that Randal is showing [https://en.wikipedia.org/wiki/Entasis Entasis] with [[Cueball]] repairing the aesthetic appearance of the middle column by making it more convex in shape, making the columns appear parallel by correcting the optical illusion of bowed columns.

The title text refers to how {{w|dynamite}}, an explosive, often used to have detonator boxes (aka. {{w|blasting machine}}s) which also looked similar to the top part of the box (without the lower whisker). These detonators were most commonly used for mining, with long wires leading to the explosives. Modern blasting machines are operated by push buttons and key switches, but the old push-handle design still resonates in the public consciousness today, due to its exposure in classic slapstick cartoon shorts like {{w|Looney Tunes}}, especially often used by {{w|Wile E. Coyote and the Road Runner|Wile E. Coyote}} against the Road Runner. See [https://youtu.be/0R66Fvhx0vQ?t=1m2s this compilation] for examples.

The title text thus warns against this kind of data inflation, since sometimes it can go awry and lead to explosions. [[Randall]] has often made comics about presenting data as more important that they are, in one way or another, and this comics clearly falls into that category. See for example [[882: Significant]], [[1132: Frequentists vs. Bayesians]], [[1478: P-Values]] and [[1574: Trouble for Science]], and this one for manipulating the way data is presented: [[558: 1000 Times]].

A box plot was also used in [[539: Boyfriend]], maybe the only other time in xkcd. There are many other types of [[:Category:Charts|data carts]] that have their own subcategories, but not this type.

==Transcript==
:[A box plot with three data points are shown. Each point consist of a standing rectangular box shaded gray and from each end of the box there extend a whisker which ends in a short line orthogonal to the whiskers line. The middle box is the longest and extends both above and below the other two, as does its whiskers. The first box is larger than the last, but those two are at the same level at their bottoms. But the bottom whisker of the first is longer than the last. If the middle box is about 1.9 cm high it will have a 1 cm whiskers below and an 0.8 cm whisker at the top for a total length of 3.7 cm. Then the first box would be 1.7 cm high with the bottom whisker 0.8 cm, and the top whisker 0.5 cm for a total length of 3 cm. The last box is then 1.4 cm high with the top whisker being 0.6 cm and the bottom 0.5 cm, for a total length of 2.5 cm. The boxes are 0.7 cm wide and the end lines for the whiskers are 0.5 cm wide. The data points stay in the same place and have the same dimensions through all five panels, except the middle point which changes as explained below in the last two panels.]

:[Cueball walks into the panel from the left looking up at the top of the first box.]

:[Cueball climbs on to the first box, by holding on to the top and stem of the first whisker, while putting a bend leg on the top of the box, while the other legs hangs down the side of the box.]

:[Cueball now stands on top of the plot, with one foot on the first box and a second foot on the middle box. He is bend over the whisker on the middle box, holding on to it with both hands, one on either side of the middle stem. He is pushing it up and down, as indicated with two light gray version of Cueball's arms and the stem, with the stem in the top gray version being about 0.1 cm above the original height and with Cueball thus with more bend arms than in the normal black version. He has thus pulled the "lever" a bit further up. The second gray version is in between these two, about 0.2 cm below the upper gray, and thus 0.1 cm below the original position and thus with a bit less bend arms that the top gray. In the final black version where the arms are almost stretched, the top is now only 0.5 cm over the box, 0.3 cm below the original position, further 0.2 cm below the second gray. On top of all this the middle box also increases its width bulging out in the top part with a maximum bulge around 0.6 cm below the top, to a width of 1.1 cm. That the movement of Cueball goes both ways are indicated both with 6 small double lines around Cueball's shoulders, arms and hands, but also by the sound his actions make:]
:''Pump''
:''Pump''
:''Pump''

:[Finally Cueball has climbed down and walks away to the right, the panel panning a bit after him so the inflated box plot moves to the left in the panel. The middle box is now inflated evenly so the maximum bulge is at the middle and it is almost touching the other two boxes with a width of 1.4 cm, double the original thickness. There have all the time been 1.5 cm between the edges of the two other boxes, so the inflated box does not interfere with the other two, but is very close to their edges. The whisker at the bottom of the middle box is unchanged but the top whisker ended up being only 0.6 cm high, 0.2 cm lower than original position, but a 0.1 cm higher than when Cueball pushed down on it in the previous panel.]

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Chart]]
[[Category:Science]]