Transaction signing is the use of a cryptographic key to attach a digital signature to a transaction. The signature proves that the transaction was authorized by the holder of the key and helps detect tampering after it is created. In secure systems, signing usually covers the important fields of a payment, transfer, contract action, or blockchain operation so that even a small change invalidates the signature.
This matters because attackers often try to alter transaction data, replay old requests, or forge approvals. Proper signing blocks those attacks when private keys are protected and verification is done correctly. In real defenses, transaction signing supports non-repudiation, audit trails, and integrity checks. In practice, security teams must manage key storage, rotation, and algorithm choice carefully, because weak implementations can make a signed transaction look trustworthy even when the system is compromised.