Could The Internet Send You The WRONG Thing?

Learn about checksums and their many uses - including ensuring data gets from one place to the other without being changed in transit.

File checksum utilities:

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[juaniththomas]

yes my son got sent adult videos after he tried to download homework questions, the internet is scary

[miigon]

Programmer here: Linus mentioned that the data goes through a CRYPTOGRAPHIC hash. While they certainly can be used to verify file integrity, more commonly used for such purpose are NON-cryptographic hash algorithms since they are generally faster. While the cryptographic ones are generally reserved for well, cryptography. (Difference: Protection against active malicious manipulation vs just plain transmission damage)

What makes a hash function cryptographic(or not)? Basically it's how hard it is for a bad actor to crack (or produce a collision). MD5 is once considered a cryptographic hash and are popular among website as a mean as storing password, but has since been deprecated and regarded as a non-cryptographic hash just for file integrity verification after people start finding fast ways to crack MD5 hashes

[CarlosCabrera-knjb]

Actually Linus, as a CS Major it’s actually a miracle that information gets from point A to point B, fucking magic man, that’s why those low level devs always have a long beard, they’re magicians.

[demophoon]

Fun fact, every credit/debit card has a checksum built into the number so computers can quickly determine if users accidentally typoed their number in wrong when paying for things online. Many other numbers which humans are expected to enter manually usually are designed with these sorts of checks in mind like insurance numbers, IMEI numbers and even those lil survey codes you find on receipts

[redaceFR]

7-zip can generate the checksums of files too ! It's the CRC option in the 7-zip menu in the explorer. It avoids downloading something else to check it or typing a command.

[danimayb]

Checksums are redundant pieces of information added to data that allow the receiver to verify if the data was received correctly. A simple checksum is to use only the first seven of the 8 bits in a byte for data. The eighth bit is a sum of the first 7 bits (modulo 2) that acts as a check for the first 7 -therein the name 'checksum'. In a nutshell :)

[JV-pukx]

Data transmitted with UDP does not get resent. The UDP protocol is used for things like video streaming where an occasional dropped packet won't be missed.

[theyruinedyoutubeagain]

Not all CRCs are cryptographic, actually I'm pretty sure most fast checksums are not crypto hardened. Still, great video!

[JV-pukx]

I've heard that many of the free cloud storage services use checksums to save space. They run the hash and compare to what is already on their servers. If two matching files are uploaded, only one copy gets stored. It does not matter if the files were uploaded to separate accounts, only one copy is actually stored.

[thoria]

I'm kind of surprised there was no mention of block-level CRC for storage media, the checksum that makes it possible for RAID-scrubbing to find faults, and for disks in general to be reasonably certain they're reading back the same values that were written in the first place, something almost everyone takes for granted.

[soup]

personally i prefer the method of looking at the files and going "Yeah that seems about right"

[VFPnkQT]

There is a big difference between *Cryptographic* checksum and the one used for verification that a file arrived correctly such as TCP/IP protocol

[SuperFromND]

if you have 7-zip installed (which you really should if you don't, it's amazing), it actually adds all sorts of checksum-generation options to the right-click menu in windows, its really handy

[trzw]

Noteworthy that a checksum on the download page being the same as the downloaded file doesn't mean that it hasn't been tampered with. If you're man in the middle-d or the site is compromised enough, hackers could also just replace the hash shown on the site to match the modified file.

[Bacender]

Hashtab is one of the best checksum tools for Windows. It adds a tab in the properties dialog of a file to let you compare checksums.

[Schalari]

This is the MOST informative Video I´ve watched so far. Thanks!!

[delofon]

1:33 If those bad actors could replace the download with a malicious one on some website, it would be of no hassle for them to replace the checksum as well. MITM attacks are guarded against with protocols like SSL. Checksums are not used to validate the security of a file but rather to confirm it was downloaded correctly from the origin (even though TCP handles it too) so that, in the worst case scenario, your PC doesn't break down from an incorrect OS download.

[ArdentMoogle]

And we're slowly moving to quantum-resistant hash functions, to avoid the issue of quantum computing in the future.

[SamarthCat]

4:23 not every service uses TCP, for example, most online games and realtime apps use UDP to reduce latency because packets don't have to arrive correctly.

[semmu]

i expected you to talk about error correction codes and how they are used in transmit, would love to see a video of it from you!