1 00:00:00,000 --> 00:00:04,340 The internet is amazing. You're streaming movies, downloading games, uploading files 2 00:00:04,340 --> 00:00:10,300 to the cloud, and somehow, all that data, mostly, gets from one place to another without 3 00:00:10,300 --> 00:00:15,420 getting corrupted. I mean, it's a miracle, isn't it? No, it's not. It's computer science. 4 00:00:15,420 --> 00:00:20,580 In particular, we owe this modern marvel to checksums, numbers that are used to verify 5 00:00:20,580 --> 00:00:27,100 that a file got sent or copied properly. But how does a simple number manage to perform 6 00:00:27,100 --> 00:00:32,160 this essential function? Well, it works thanks to cryptography. Even if the data that you're 7 00:00:32,160 --> 00:00:38,120 transmitting isn't encrypted, or even particularly sensitive, in applications that use checksums, 8 00:00:38,120 --> 00:00:43,980 the protocol will run the contents of the file through a cryptographic hash function, which 9 00:00:43,980 --> 00:00:50,460 is basically a complicated math function that produces a lengthy and unique string of characters. 10 00:00:50,460 --> 00:00:54,960 The reason this works well for generating checksums is that if you change even one 11 00:00:55,040 --> 00:01:01,200 byte of data, even in a very large file, that string of characters, or hash, will change 12 00:01:01,200 --> 00:01:07,200 completely. And this is actually the same way that passwords are stored securely on websites. 13 00:01:07,200 --> 00:01:11,640 Except, instead of storing the password in plain text, they're run through a hash function 14 00:01:11,640 --> 00:01:17,440 that is virtually impossible to reverse. That way, if a hacker breaks into the server, 15 00:01:17,440 --> 00:01:22,040 they only see a pretty much meaningless hash rather than your plain text password. 16 00:01:22,040 --> 00:01:26,840 So coming back to checksums, they play an important role in digital security as well. 17 00:01:26,840 --> 00:01:31,160 If you download a file from the internet, you make the assumption that the host is providing 18 00:01:31,160 --> 00:01:38,560 you a safe, non-malicious file. But bad actors can sometimes attempt to attack PCs by replacing 19 00:01:38,560 --> 00:01:43,160 files that are commonly downloaded. That's why many responsible websites will provide 20 00:01:43,160 --> 00:01:48,240 a checksum so that you can verify that the file you download is exactly what it's supposed 21 00:01:48,240 --> 00:01:53,440 to be. So, with this level of importance, you would think that checksums are ubiquitous 22 00:01:53,440 --> 00:01:59,360 in computing. But actually, that's not the case. In fact, in Windows, File Explorer 23 00:01:59,360 --> 00:02:04,760 doesn't use checksums by default when performing a file transfer. Even though generating a checksum 24 00:02:04,760 --> 00:02:09,680 would take a trivial amount of time for small files like Word documents, it can take a lot 25 00:02:09,680 --> 00:02:14,440 more time if you're trying to move around many gigabytes worth of data. However, there 26 00:02:14,440 --> 00:02:18,440 are ways to work around this. If you want to compare the checksum of a copied file to 27 00:02:18,440 --> 00:02:23,520 the original in Windows, all you have to do is fire up a command prompt and type in this 28 00:02:23,520 --> 00:02:27,680 command followed by the file path. Because checksums will be very different if the file 29 00:02:27,680 --> 00:02:32,220 contents don't match, you can usually just glance at them instead of tediously comparing 30 00:02:32,220 --> 00:02:36,640 them character by character. You can also get third-party tools that do generate and 31 00:02:36,640 --> 00:02:40,000 validate checksums when you copy files, and we're going to have one of those linked down 32 00:02:40,000 --> 00:02:45,280 below. Did you know that you can select Validate files in Steam if one of your games isn't 33 00:02:45,280 --> 00:02:50,220 running correctly? The service stores checksums of known good game files, so when you click 34 00:02:50,220 --> 00:02:54,760 this button, it compares them to the checksums of the files that are stored on your PC. If 35 00:02:54,760 --> 00:02:58,760 there's any discrepancy, the altered file can be quickly downloaded and replaced with 36 00:02:58,760 --> 00:03:03,240 the original rather than forcing you to reinstall the entire game like we had to do in the old 37 00:03:03,240 --> 00:03:08,120 days. And if you're a video editor, popular editing programs like Adobe Premiere support 38 00:03:08,120 --> 00:03:12,840 the use of checksums to verify large media files to ensure that they don't get corrupted 39 00:03:12,840 --> 00:03:17,240 when you're copying them. Microsoft's OneDrive cloud storage solution for Windows also makes 40 00:03:17,240 --> 00:03:21,720 use of checksums, in this case to make sure that your photos and documents were uploaded 41 00:03:21,720 --> 00:03:26,240 properly. And if you need to transfer lots of files at once, you can use checksums for 42 00:03:26,240 --> 00:03:31,840 zipped folders to quickly verify that all of your files are in good shape. In fact, 43 00:03:31,840 --> 00:03:37,800 TCPIP, the data transmission protocols that underpin the internet, use checksums on every 44 00:03:37,800 --> 00:03:42,920 packet of data to make sure that no bits were flipped in transit. If the checksum that 45 00:03:42,920 --> 00:03:47,720 was sent doesn't match the checksum generated by the receiver, that packet gets dropped 46 00:03:47,720 --> 00:03:52,400 and retransmitted. So basically, every bit of data that you get from the internet goes 47 00:03:52,400 --> 00:03:58,320 through this verification process. Which is cool, but keep in mind that this kind of checksum 48 00:03:58,320 --> 00:04:03,840 doesn't really improve your security. As, like I said, a file could contain malware 49 00:04:03,840 --> 00:04:09,160 from its origin, whether on purpose or due to a bad actor. So it's still very important 50 00:04:09,160 --> 00:04:14,000 that you take caution when dealing with files from unknown sources, as we learned ourselves 51 00:04:14,000 --> 00:04:19,920 the hard way recently. So go watch this video next to learn about how we recently got our 52 00:04:19,920 --> 00:04:25,640 channel hijacked, because it could happen to you too. Thanks for watching, like or dislike, 53 00:04:25,640 --> 00:04:30,920 check out our other videos, and leave a comment if you have a future TechWiki video suggestion. 54 00:04:30,920 --> 00:04:33,800 We don't call it that anymore. I'm rusty.