Cheat sheet of the cryptographic hashes powering Bitcoin

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1- Core Bitcoin Hashes

SHA-256

• Mining (Proof of Work): miners hash block headers
• Transaction IDs (txid): each transaction gets a unique SHA-256 hash
• Merkle tree construction (organizing transactions in blocks)

SHA-256d (Double SHA-256)

• Block hashes (each block header hashed twice)
• Extra security against length extension attacks
• Checksums in addresses

RIPEMD-160

• Address generation: RIPEMD160(SHA256(pubkey))
• Shortens 256-bit SHA-256 into 160-bit hash

HASH-160 (SHA-256 + RIPEMD-160)

• Used in P2PKH & P2SH addresses

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2- Wallet & Key Management Hashes

HMAC-SHA256 / SHA512

• Key derivation in BIP32 (HD wallets)
• Secure key stretching

HKDF

• BIP-324 encrypted P2P transport
• Secure key expansion from master keys
• Advanced key derivation

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3- Networking & Protocol

SipHash-2-4

• Short IDs in Compact Block relay (BIP-152)
• DoS protection
• Fast hash for hash tables
• Prevents hash collision attacks

MuHash


• Accumulators for UTXO set commitments (useful for AssumeUTXO, UTXO snapshots)

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4- Encryption (Not Core Bitcoin)

ChaCha20

• Stream cipher for encrypting data
• Used in BIP324 (v2 P2P transport encryption)

Poly1305

• Works with ChaCha20 for authenticated encryption
• Ensures data integrity

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SHA-3 (SHA3-256)

• Not used in Bitcoin itself. It’s only needed for Tor v3 onion addresses (ed25519 → onion domain)