Cryptography
Hash functions, signatures and elliptic curves, the tools that make Bitcoin secure.
Hash functions
A hash function turns any data into a short, fixed-size fingerprint, and one changed letter changes it completely. Try it live and see how Bitcoin uses it.
SHA-256
SHA-256 is the hash function Bitcoin uses for blocks, transaction IDs and mining, usually applied twice. Learn how it works and test it live.
HASH160 and RIPEMD-160
HASH160 is SHA-256 followed by RIPEMD-160. It turns a 33-byte public key into the 20-byte hash inside most Bitcoin addresses. See how and why.
Hexadecimal
Hex writes each byte as two characters from 0-9 and a-f. Learn to read hashes, keys and raw transactions, and convert numbers with our tool.
Bytes and endianness
Bitcoin stores most numbers least-significant byte first (little-endian), which is why txids and block hashes look reversed in raw data. Learn why.
Digital signatures
A digital signature proves you hold a private key without revealing it. Learn how Bitcoin signatures authorise every spend and why they can't be reused.
Elliptic curve cryptography
Bitcoin keys live on the secp256k1 curve, y² = x³ + 7. Multiplying a point is easy and undoing it is practically impossible. See how it works.
ECDSA signatures
ECDSA is the signature scheme Bitcoin used from the start. A signature is two numbers, r and s. Learn how it works and why nonce reuse is fatal.
Schnorr signatures
Taproot introduced Schnorr signatures: a fixed 64 bytes, simpler maths, batch verification and multi-party key aggregation. Learn what changed.
Randomness and entropy
A private key is only as safe as the randomness that made it. Learn what entropy means, how weak randomness led to real thefts, and how to stay safe.