2267: Blockchain - Revision history

FaviFake: /* Explanation */

2025-07-26T14:37:50Z

‎Explanation

Davidy22: Reverted edits by Explain xkcd server admin (talk) to last revision by Jacky720

2022-05-21T02:54:32Z

Reverted edits by Explain xkcd server admin (talk) to last revision by Jacky720

Show changes

Explain xkcd server admin at 21:51, 20 May 2022

2022-05-20T21:51:13Z

Show changes

Jacky720: rv

2022-05-04T21:56:37Z

Show changes

Ex Kay Cee Dee at 21:50, 4 May 2022

2022-05-04T21:50:32Z

Show changes

Jacky720: rv

2022-05-04T21:09:57Z

Show changes

Ex Kay Cee Dee at 20:16, 4 May 2022

2022-05-04T20:16:54Z

Show changes

Davidy22: Reverted edits by X. K. C. D. (talk) to last revision by NotaBene

2022-05-04T02:13:06Z

Reverted edits by X. K. C. D. (talk) to last revision by NotaBene

Show changes

X. K. C. D. at 23:26, 3 May 2022

2022-05-03T23:26:51Z

Show changes

NotaBene: /* Explanation */

2020-06-12T17:05:50Z

‎Explanation

@@ Line 22: / Line 22: @@
 Like Blockchains, grappling hooks are thus seen as a cool tool when they encounter a problem for which they are the right solution, like boarding an enemy ship... However, just like for blockchains, in real life there are very few cases where these hooks are the best solution for a given problem.  As an example of a problem that is ''not'' well-solved by a grappling hook, see [[2128: New Robot]] where an electrically-charged "search and rescue" robot has been equipped with such a hook.
-Blockchain was previously mentioned in [[2030: Voting Software]], with Megan and Cueball expressing distrust in its use for electronic voting.
+Blockchain was previously mentioned in [[2030: Voting Software]], with Megan and Cueball expressing distrust in its use for electronic voting. Flowcharts are a [[:Category:Flowcharts|recurring theme]] in xkcd. If you are unfamiliar with them, see [[518: Flow Charts]]. Similar simple flowcharts like this comic, where there is only one reply has been used before like [[1723: Meteorite Identification]] and [[2026: Heat Index]]. See also the similar [[1691: Optimization]], where the flowchart, as it does here, asks if you are using flowcharts.
 ==Transcript==

@@ Line 10: / Line 10: @@
 This comic is a {{w|flowchart}} intended to help project leaders decide if their project needs a blockchain.
-A {{w|blockchain}} is a data storage structure shared between various computers.  Each block is digitally signed and includes the digital signature of the block before it, which makes it highly resilient against tampering.  However, what sets blockchains in the context of {{w|cryptocurrencies}} such as {{w|Bitcoin}} apart from e.g. {{w|Merkle trees}} used in programs such as {{w|Git}} is that ''anyone'' can write to a blockchain.  This is sometimes specified as a "public ledger" or "public blockchain".  In order to prevent the blockchain from being vandalized, various mechanisms are used to determine consensus about which additions to the blockchain are legitimate.  Bitcoin and most cryptocurrencies use a "{{w|proof of work}}" system, where writing a block includes some task which is computationally difficult to perform but simple to verify, such as finding a magic number (called a "{{w|cryptographic nonce}}") that, when appended to the block, makes its hash value start with lots of zeroes.  This results in a system which is, in ideal circumstances, extremely difficult to vandalize, as the attacker must find new nonce values for the block he wishes to modify and every succeeding block, and then broadcast the modified blockchain from enough nodes to convince the rest of the network to go along with it instead of the legitimate one.
+A {{w|blockchain}} is a data storage structure shared between various computers.  Each block is digitally signed and includes the digital signature of the block before it, which makes it highly resilient against tampering.  However, what sets blockchains in the context of {{w|cryptocurrencies}} such as {{w|Bitcoin}} apart from e.g. {{w|Merkle trees}} used in programs such as {{w|Git}} is that ''anyone'' can write to a blockchain.  This is sometimes specified as a "public" or "permissionless" ledger or blockchain.  In order to prevent the blockchain from being vandalized, various mechanisms are used to determine consensus about which additions to the blockchain are legitimate.  Bitcoin and most cryptocurrencies use a "{{w|proof of work}}" system, where writing a block includes some task which is computationally difficult to perform but simple to verify, such as finding a magic number (called a "{{w|cryptographic nonce}}") that, when appended to the block, makes its hash value start with lots of zeroes.  This results in a system which is, in ideal circumstances, extremely difficult to vandalize, as the attacker must find new nonce values for the block he wishes to modify and every succeeding block, and then broadcast the modified blockchain from enough nodes to convince the rest of the network to go along with it instead of the legitimate one.
 In practice, in order to actually make this so-called "51% attack" unfeasible, the network needs to have as many legitimate actors using as much computing power as possible.  This results in the Bitcoin network using approximately [https://www.statista.com/statistics/881541/bitcoin-energy-consumption-transaction-comparison-visa/ a million times more energy per transaction] than Visa's network, while smaller cryptocurrencies have actually [https://news.bitcoin.com/bitcoin-gold-51-attacked-network-loses-70000-in-double-spends/ experienced 51% attacks and double-spending].  For almost any practical project, there is no need to allow ''everyone in the world'' to have write access to a database, so it is generally quite acceptable to use a straightforward centrally-controlled permissioning system rather than proof-of-work or other decentralization schemes to restrict write access.  This is why all branches of the flowchart lead to the answer "No".