01 / input
It starts as anything.
A word, a file, a whole block of transactions. Here it's just two letters.
HASH
sha256("hash") =
Change one letter. Change everything. Scroll to hash it.
02 / mixing
Then it goes in the blender.
SHA-256 chops it up and runs 64 rounds of shuffling, rotating and mixing bits.
03 / output
Out comes a fingerprint.
Exactly 64 characters, 256 bits. Same input, same fingerprint, every time.
04 / one letter
Now change one letter.
Just m to n. Watch the fingerprint.
05 / avalanche
Everything changes.
About half of all bits flip. That's the avalanche effect, and it's why nobody can fake a hash.
input
sha256 ↓
waiting for input
Up close
256 bits. Four rules.
Keep scrolling to zoom in.
How many hashes are there
2256. One scroll.
100things counted
1digits long
One thing
Pack the block
Everything goes in.
Transactions, the time, and the last block's hash. Scroll to start mining.
0nonces tried
0leading zeros
Try it yourself
Hash anything.
Type something, then change one letter. This is real SHA-256, running right in your browser.
0characters changed
0of 256 bits flipped
Nothing you type leaves your device. Still, never type a seed phrase or password into any website.
Take it apart
What's inside SHA-256?
Hash history
The people who scrambled it first.
1953
The first hash idea
Hans Peter Luhn at IBM writes up a way to file information by chopping it into short codes. Hashing is born.
1979
Merkle's trees
Ralph Merkle shows how to hash hashes into a tree, so one short root can vouch for thousands of records.
1991
A chain of documents
Stuart Haber and Scott Stornetta link timestamped documents with hashes, so no one can backdate one. Sound familiar?
2001
SHA-256 arrives
The US government publishes the SHA-2 family, including SHA-256, as a standard anyone can use.
2009
The genesis block
On January 3, Bitcoin's first block is mined using SHA-256. Every Bitcoin block since points back to it.
Now
Quintillions a second
Bitcoin miners worldwide make hundreds of quintillions of SHA-256 guesses every second, all looking for a lucky hash.
Next
Your hash
The chain isn't finished. Someone reading this adds the next block.
Why no two hashes match
The birthday problem.
With just 23 people in a room, there's a 50% chance two share a birthday. Hashes face the same math, but with 2²⁵⁶ birthdays instead of 365, you'd need about 2¹²⁸ hashes for an even chance of one match.
1 person
Merkle tree
Thousands of transactions. One hash.
Pair them up, hash the pairs, then hash those pairs, until one root is left. Change any transaction and the root changes too.
Hashing transactions
A hash doesn't keep your secret. It proves you knew it. Change one letter, and the whole world can tell.
Mine lab
Mine a block.
Your browser is guessing for real. Find a hash that starts with enough zeros and you've mined a block. Scroll fast to overclock.
0hashes tried
0hashes a second
0blocks found
Right now
Your device
We timed your device hashing a few thousand times when the page loaded. Here's what that speed means.
0seconds on this page
0hashes you could have made
100years to guess one hash
100times the age of the universe