explain xkcd - User contributions [en]

1354: Heartbleed Explanation

2014-04-12T13:42:19Z

TaoPhoenix: /* Explanation */ Randall has two l's - spelling

{{comic
| number = 1354
| date = April 11, 2014
| title = Heartbleed Explanation
| image = heartbleed_explanation.png
| titletext = Are you still there, server? It's me, Margaret.
}}

==Explanation==
{{incomplete|PLEASE don not remove this TAG that fast!!! Many issues still have to be solved here.}}
The {{w|Heartbleed bug}} has received a lot of news coverage recently and was also the topic of the previous comic [[1353: Heartbleed]]. This comic explains how the bug may have been discovered and can be exploited to reveal a server's memory contents. A hypothetical cracker [[Megan|Meg]] sends heartbeat requests to the server, the server responds to the heartbeat request by returning the contents of the body of the request up to the number of letters requested. The first two requests are well formed, requesting exactly the number of characters in the request body. The server's memory is showing Meg's request with many other requests going on at the same time.

The last request asks for "HAT" but requests that it be 500 letters long; the server — not checking if or simply unaware that 500 letters is larger than the request body — returns "HAT" plus 497 letters that happened to be next to the word "HAT" in its memory. Included are many sensitive bits of information, including a master key and user passwords. One of the passwords shown is "CoHoBaSt", a reference to [[936: Password Strength]], which suggests using "correct horse battery staple" as a password.

Often popular explanations of security bugs require the issue to be simplified a lot and to leave out a lot of details. In this case Randall didn't have to do much simplifying; the bug is actually that simple. Also, it should be noted that any client which can connect to the server typically can exploit this bug in the underlying OpenSSL software — the use of the term "User Meg" does not imply that Meg had to authenticate first.

The title text is a reference to ''{{w|Are You There God? It's Me, Margaret.|Are you there God? It's me, Margaret.}}'' a novel by Judy Blume, and plays off of the "server, are you still there?" line in every panel where she did start a request. ''Meg'' can be a nickname for ''Margaret'' as well as ''Megan'', which perhaps explains why the character's usual name, Megan, is abbreviated here.

==Transcript==

:How the Heartbleed bug works:

:Megan: Server, are you still there? If so, reply "POTATO" (6 letters).
:The server's memory is shown: ...<tt>wants pages about boats. User Erica requests secure connection using key "4538538374224". '''User Meg wants these 6 letters: POTATO.''' User Ada wants pages about "irl games". Unlocking secure records with key 5130985733435. Maggie (chrome user) sends this message: "Hi</tt>...

:Server shows the same memory content but POTATO is highlighted.
:Server: <tt>POTATO</tt>

:Megan: Server, are you still there? If so, reply "BIRD" (4 letters).
:The server's memory is shown: ...<tt>User Olivia from London wants pages about "mad bees in car why". Note: Files for IP 375.381.283.17 are in /tmp/files-3843. '''User Meg wants these 4 letters: BIRD.''' There are currently 346 connections open. User Brendan uploaded the file selfie.jpg (contents: 834ba962e2ceb9ff89bd3bff8c</tt>...

:Server shows the same memory content but now with BIRD highlighted.
:Server: <tt>BIRD</tt>
:Megan: ''Hmm...''

:Megan: Server, are you still there? If so, reply "HAT" (500 letters).
:Server memory: ...<tt>a connection. Jake requested pictures of deer. '''User Meg wants these 500 letters: HAT.''' Lucas requests the "missed connections" page. Eve (administrator) wants to set server's key to "14835038534". Isabel wants pages about "snakes but not too long". User Karen wants to change account password to "CoHoBaSt". User</tt>...

:Server shows the same memory content, highlighting the first 500 letters of the memory beginning at HAT.
:Server: <tt>HAT. Lucas requests the "missed connections" page. Eve (administrator) wants to set server's key to "14835038534". Isabel wants pages about "snakes but not too long". User Karen wants to change account password to "CoHoBaSt". User Amber requests pages</tt>...
:Megan writes this all down.

{{comic discussion}}
[[Category:Comics featuring Megan]]
[[Category:Computers]]

1352: Cosmologist on a Tire Swing

2014-04-08T11:41:21Z

TaoPhoenix: /* Explanation */spelling

{{comic
| number = 1352
| date = April 7, 2014
| title = Cosmologist on a Tire Swing
| image = cosmologist_on_a_tire_swing.png
| titletext = No matter how fast I swing, I can never travel outside this loop! Maybe space outside it doesn't exist! But I bet it does. This tire came from somewhere.
}}

==Explanation==
[[Cueball]] and a curious child walks through a forest with many small pools/lakes. The setting of trees interspersed with these many small pools resembles the {{w|Wood between the Worlds}}, a meta-verse described in C.S. Lewis's ''{{w|The Magician's Nephew}}''; each pool leads into a different universe — one of these is ours, another is {{w|Narnia}} and the world of the {{w|White Witch}} is also visited through these pools.

The girl ask about the time before the {{w|Big Bang}} and Cueball tells there where no time before - a common theory. But then they happen upon a {{w|cosmologist}} on a swing who has several other theories about the universe...

Simply put, the tire swing is a symbolic representation of our universe. Scientific observations tell us that both space and time began with the {{w|Big Bang}} ~13.8 billion years ago. We don't know if there was such a thing as "before" the universe, or what that might be.

The first 6 panels reference ongoing speculation about where the universe came from and why it even exists in the first place. The last 2 panels relate to recent observations of the {{w|accelerating universe}} in which galaxies are now receding from each other at higher and higher speeds, due to {{w|dark energy}}.

The swing itself is likely a reference to the {{w|Cyclic Model}}, where the universe expands from a Big Bang, then contracts back in on itself under its own gravity for a {{w|Big Crunch}}, before bouncing outward again in another Big Bang, and repeating the whole process. On the other hand the swing is accelerating as the universe - so it may also be a reference to the entire universe. We are all "trapped" on this swing - and it is accelerating!

The title text references questions about the {{w|shape of the universe}} (which may as well be donut shaped like a tire) and what could lie "outside" of it. We can't see outside of the {{w|observable universe}}, but it's likely that the universe is bigger than the observable universe and uniform on large scale. Even though nobody can leave our own universe, the cosmologist ([[Randall]]?) bets that such unknown worlds do exist.

==Transcript==
:Girl: What was before the big bang?
:Cueball: I think time began with the big bang. So it doesn't make sense to ask what came before it.
:Cosmologist (off panel): ''Look out''

:Cosmologist: ''WHEEEE'' Hi I'm a cosmologist on a tire swing!

:Cosmologist: We don't know whether time

:Cosmologist: started at the big bang.

:Cosmologist: It might have!

:Cosmologist: Or maybe not! We don't know!
:Cueball: Oh. OK!

:Girl: ...Your tire swing looks fun!
:Cosmologist: I can't stop!

:Girl: Won't the swing stop on its own?
:Cosmologist: I thought it would, but it seems to be accelerating.
:Girl: Cosmology sounds pretty confusing.
:Cosmologist: ''WHEEEEE!''

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Astronomy]]
[[Category:Science]]

1352: Cosmologist on a Tire Swing

2014-04-08T11:40:57Z

TaoPhoenix: /* Explanation */ spelling

{{comic
| number = 1352
| date = April 7, 2014
| title = Cosmologist on a Tire Swing
| image = cosmologist_on_a_tire_swing.png
| titletext = No matter how fast I swing, I can never travel outside this loop! Maybe space outside it doesn't exist! But I bet it does. This tire came from somewhere.
}}

==Explanation==
[[Cueball]] and a curios child walks through a forest with many small pools/lakes. The setting of trees interspersed with these many small pools resembles the {{w|Wood between the Worlds}}, a meta-verse described in C.S. Lewis's ''{{w|The Magician's Nephew}}''; each pool leads into a different universe — one of these is ours, another is {{w|Narnia}} and the world of the {{w|White Witch}} is also visited through these pools.

The girl ask about the time before the {{w|Big Bang}} and Cueball tells there where no time before - a common theory. But then they happen upon a {{w|cosmologist}} on a swing who has several other theories about the universe...

Simply put, the tire swing is a symbolic representation of our universe. Scientific observations tell us that both space and time began with the {{w|Big Bang}} ~13.8 billion years ago. We don't know if there was such a thing as "before" the universe, or what that might be.

The first 6 panels reference ongoing speculation about where the universe came from and why it even exists in the first place. The last 2 panels relate to recent observations of the {{w|accelerating universe}} in which galaxies are now receding from each other at higher and higher speeds, due to {{w|dark energy}}.

The swing itself is likely a reference to the {{w|Cyclic Model}}, where the universe expands from a Big Bang, then contracts back in on itself under its own gravity for a {{w|Big Crunch}}, before bouncing outward again in another Big Bang, and repeating the whole process. On the other hand the swing is accelerating as the universe - so it may also be a reference to the entire universe. We are all "trapped" on this swing - and it is accelerating!

The title text references questions about the {{w|shape of the universe}} (which may as well be donut shaped like a tire) and what could lie "outside" of it. We can't see outside of the {{w|observable universe}}, but it's likely that the universe is bigger than the observable universe and uniform on large scale. Even though nobody can leave our own universe, the cosmologist ([[Randall]]?) bets that such unknown worlds do exist.

==Transcript==
:Girl: What was before the big bang?
:Cueball: I think time began with the big bang. So it doesn't make sense to ask what came before it.
:Cosmologist (off panel): ''Look out''

:Cosmologist: ''WHEEEE'' Hi I'm a cosmologist on a tire swing!

:Cosmologist: We don't know whether time

:Cosmologist: started at the big bang.

:Cosmologist: It might have!

:Cosmologist: Or maybe not! We don't know!
:Cueball: Oh. OK!

:Girl: ...Your tire swing looks fun!
:Cosmologist: I can't stop!

:Girl: Won't the swing stop on its own?
:Cosmologist: I thought it would, but it seems to be accelerating.
:Girl: Cosmology sounds pretty confusing.
:Cosmologist: ''WHEEEEE!''

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Astronomy]]
[[Category:Science]]