Big thank you to DeleteMe for sponsoring this video. Use my link http://joindeleteme.com/Bombal to receive a 20% discount or use the QR Code in the video. 

In this interview, David Bombal sits down with Dr. Mike Pound (Computerphile) to clear up one of the biggest crypto misconceptions on the Internet: hashing is not encryption, and hash functions are not reversible. 

In this video you’ll learn what a hash function actually does (a deterministic, fixed-length, “random-looking” summary of data) and why the whole point is that you cannot take a hash and reconstruct the original file. Dr Mike explains the key properties of secure hashing, including the avalanche effect (tiny input change, massive output change), and why older algorithms like MD5 and SHA-1 became unsafe due to collisions. We also cover what “collisions” really mean, why they must exist in theory (the pigeonhole principle) and why they can appear sooner than expected (the birthday paradox). 

Then we tackle the YouTube-comments classic: rainbow tables. If hashes are one-way, how do attackers “crack” passwords? The answer: they don’t reverse hashes. They guess passwords, hash them forward, and match the results. Mike breaks down how rainbow tables speed this up with precomputed hashes, and why salting makes those precomputations far less effective by forcing attackers to redo work per user. 

Finally, we zoom out into modern cryptography: why SHA-2 is widely used today, why SHA-3 exists as a structurally different backup option, what length extension attacks are, and what quantum computing changes (and doesn’t change) for hashing and encryption. We also touch on how hashes power digital signatures, file integrity checks (like verifying an ISO download), and why AES dominates symmetric encryption. 

// Mike's SOCIAL // 
X: https://twitter.com/_mikepound  

// YouTube Video REFERENCE // 
SHA: Secure Hashing Algorithm: https://youtu.be/DMtFhACPnTY?si=HFPs-T_3Dn_U7Er4
Birthday Paradox: https://youtu.be/jsraR-el8_o 
The Next Big SHA? SHA3 Sponge Function Explained: https://youtu.be/fzlflyw7X2I?si=csnfTzLZoAPE681q

// David's SOCIAL //  
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SoundCloud:  https://soundcloud.com/davidbombal 
Apple Podcast:  https://podcasts.apple.com/us/podcast/david-bombal/id1466865532 

// MY STUFF // 
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// SPONSORS //  
Interested in sponsoring my videos? Reach out to my team here: sponsors@davidbombal.com 

// MENU // 
0:00 - Coming up 
01:09 - DeleteMe sponsored segment 
02:54 - Hashing is not Encryption // Encryption and Hashing explained 
09:47 - Hash functions are irreversible 
15:22 - How hashing works 
17:23 - Why MD5 is bad 
20:09 - Recommended hashing function 
21:47 - Birthday paradox explained 
23:39 - Rainbow table explained 
29:44 - Salting explained 
33:35 - Pigeon Hole principle explained 
36:35 - SHA-2 is the answer 
37:17 - SHA-3 vs SHA-2 
40:42 - The effect of quantum computing 
42:47 - Quick summary 
43:52 - Sign-In with private key 
45:21 - Avalanche effect explained 
49:10 - Where to learn more about hash functions 
50:27 - Conclusion 

Please note that links listed may be affiliate links and provide me with a small percentage/kickback should you use them to purchase any of the items listed or recommended. Thank you for supporting me and this channel!  

Disclaimer: This video is for educational purposes only. 

#cryptography  #hashing #encryption

Why Hashes Are NOT Reversible: Rainbow Tables and Collisions EXPLAINED