Crypto glossary
Digital signature
A digital signature is cryptographic proof, created with a private key, that a message or transaction was approved by the key's owner and has not been altered.
Every blockchain transaction must be signed. The wallet combines the transaction data with the private key to produce a signature, and anyone can check it with the matching public key, without ever learning the private key. If even one character of the transaction changes, the signature no longer verifies, so nodes reject it.
Bitcoin and Ethereum use the ECDSA scheme on the secp256k1 curve, and Bitcoin added Schnorr signatures with Taproot in November 2021, which make some multi-party spends cheaper and more private. Wallets also sign plain messages, for example to log into a dApp or prove ownership of an address, and token approvals are often granted through signed off-chain messages.
A signature is only as safe as the key behind it and the attention of the signer. Many thefts come from users signing malicious approvals or messages they did not read, and large quantum computers could one day threaten today's signature schemes.
Example
To prove control of a wallet holding 5 BTC without moving funds, its owner signs the message "Audit 2026" and an auditor verifies the signature against the address.
