#️⃣ Hashing Deep Dive: One-Way Cryptography
Understand why you can't reverse a hash—and why that's perfect for blockchain
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0 / 5 completed👆 Hashing Deep Dive
Hash functions are one-way mathematical transformations that create unique digital fingerprints. Change one bit of input, and the entire hash changes!
🎮 Interactive Hash Generator
Try changing just one character and see how the hash completely changes!
🔬 Three Critical Properties
Same input always produces the same hash. Hash "Hello" 1000 times = same result.
Tiny input change = completely different hash. Change 1 bit → 50% of hash bits flip.
Impossible to reverse. Given hash, you cannot find the original input (except brute force).
🔐 Common Hash Functions
Used by Bitcoin - 256-bit output (64 hex characters). Industry standard for security.
Used by Ethereum - Different algorithm than SHA-2 family. Latest NIST standard (2015).
DEPRECATED - Do NOT use for security! 128-bit output. Collisions found in 2004. Only for checksums.
DEPRECATED - 160-bit output. Collision found in 2017 (SHAttered attack). Replaced by SHA-256.
⚔️ Collision Resistance
A collision is when two different inputs produce the same hash. Good hash functions make collisions computationally infeasible.
For a hash with n bits, you need roughly 2^(n/2) attempts to find a collision.
Researchers found mathematical shortcuts to generate collisions much faster than brute force. MD5 in seconds, SHA-1 in days. SHA-256 still secure!
💡 Key Takeaways
You cannot decrypt a hash back to the original input. It's a fingerprint, not an envelope.
Change one bit in a gigabyte file, and the entire hash changes. Perfect for detecting tampering!
MD5 and SHA-1 are broken. Bitcoin uses SHA-256, Ethereum uses SHA-3. Both are secure.