Implementations of the present disclosure include receiving, by a consensus node of a blockchain, transaction data and a digital signature of the transaction data. The transaction data includes a commitment value, a random number, and a transaction amount to be transferred from one of a public account or a private account of the first user node to one of a public account or a private account of asecond user node. The consensus node verifies the digital signature of the transaction data using a public key of the first user node. It then determines that the transaction amount is valid, if the commitment value is correct based on the random number and the commitment scheme, and the transaction amount is less than or equal to a balance of the one of the public account or the private account of the first user node before transfer of the transaction amount.