Block data processing method, device and system

The embodiment of the invention provides a block data processing method, device and system, relates to the technical field of block chains, and can also be used in the financial field, and the method comprises the steps: receiving a secret file sent by a service gateway, and storing the secret file; and generating a content identifier corresponding to the file content of the encrypted file and carrying out data copy broadcasting, so that a blockchain node executes an evidence storage processing smart contract after receiving an initialized security parameter and a file evidence storage request sent by the service gateway, and stores the user public key and the master key, generating a new block by the block chain node according to the content identifier, generating a symmetric key according to the user public key after the new block is confirmed, and returning the symmetric key to the user through the service gateway and the client; according to the method and the device, on-chain and off-chain data transmiss