What it looks like
Random entropy is simply bits: unpredictable zeroes and ones. Sixteen random bytes give 128 bits, enough for a 12-word BIP39 phrase after adding a checksum.
Bitcoin Entropy Lab
Information about entropy
Entropy is uncertainty that an attacker must guess. A wallet needs enough unpredictable entropy to create private keys no one else can reproduce.
2128
possible starting values
What can go wrong
Dates, quotations, repeated patterns, biased coins, and human-chosen words occupy tiny, guessable corners of the possible range. More characters do not automatically mean more entropy.
How wallets do it
Good wallets use a cryptographically secure random-number generator, ideally with hardware randomness and health checks. Generate keys in a trusted wallet or signing device, never on this page.
Interactive microscope
Build and inspect uncertainty
Learning only. Never use entropy shown by a website to protect real bitcoin.
Ask the operating system
The browser requests cryptographically secure bytes from your device. Regenerating should change roughly half the squares.
Flip a fair coin
Record the result before flipping again. One independent fair flip can contribute one bit. Keyboard: H or T.
Roll a fair six-sided die
Each independent roll carries about 2.58 bits. A real conversion must remove modulo bias; the raw three-bit display below is only a visual trace.
Watch humans make patterns
Type anything. The estimate measures variety inside this sample, not how difficult your idea is to guess from dictionaries or personal information.
Capture a changing environment
Images, movement, and sound contain variation, but their true unpredictability is unknown. Capture a sample, inspect its fingerprint, then mix it with secure device randomness.
Move your pointer inside the field
Microphone audio stays in this browser and is discarded after its fingerprint is made.
Choose an environmental source.
Secure device128 / 128 bits
Cryptographic source- Recorded
- 128 bits
- Balance
- Checking…
- Longest run
- Checking…
- Average guess
- Checking…
Hexadecimal view
What entropy protects
One secret in an unthinkably large space
A wallet deterministically derives many private keys from one starting secret. These fingerprints demonstrate that branching behavior without creating recovery words, real private keys, or Bitcoin addresses.
Symbolic map, not to scale2^128 possible secrets
Starting secret fingerprint
Calculating…Demo branch 0
—Demo branch 1
—Demo branch 2
—These are domain-separated SHA-256 teaching fingerprints. They illustrate deterministic derivation but are deliberately not usable wallet credentials.
Change one bit
The descendants become unrelated
Flip one bit in the starting entropy and compare its demonstration fingerprint. A good cryptographic function changes roughly half its output bits.
—of 256 bits changed
Brute-force race
Guessing a 128-bit wallet
Watch an imaginary attacker test one trillion candidates every second. The counter moves quickly; its share of the full keyspace effectively does not.
- Guesses simulated
- 0
- Keyspace searched
- 0%
- Average time
- —
Under the hood
Entropy becomes word indexes
BIP39 does not pick twelve words independently. It starts with entropy, appends checksum bits derived from SHA-256, then cuts the result into 11-bit indexes for a 2,048-word list.
128entropy bits
4checksum bits
12BIP39 words
1 · Append the checksum
Entropy bits SHA-256 checksum
Split every 11 bits
Each 11-bit group is a number from 0 to 2,047: an index into the selected BIP39 wordlist. Hover or focus an index to see exactly which bits created it. The words themselves are intentionally not shown.
Attacker's view
Small bit counts collapse quickly
Move the control to change the search space. This assumes an unrealistically favorable attacker trying one trillion guesses every second.
Possible values2^32Average guessing timeless than a second