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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.
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// YouTube Video REFERENCE //
SHA: Secure Hashing Algorithm: • SHA: Secure Hashing Algorithm - Computerphile
Birthday Paradox: • Hash Collisions & The Birthday Paradox - C...
The Next Big SHA? SHA3 Sponge Function Explained: • The Next Big SHA? SHA3 Sponge Function Exp...
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Disclaimer: This video is for educational purposes only.
#cryptography #hashing #encryption