A computer-implemented method, performed by a server end, for updating data in blockchain, the method comprising: obtaining (511, 521), from a client, one or more requests for updating data in one or more blockchains, comprising obtaining one or more local accounts associated with one or more users of the client, one or more unsigned blockchain transactions to be executed for correspondingly updating a plurality of pieces of data stored in the one or more blockchains and associated with the one or more local accounts, information of the plurality of pieces of data for updating the plurality of pieces of data, and one or more identifications of the one or more blockchains corresponding to the one or more blockchain transactions, wherein the information of the plurality of pieces of data comprises new data to add to the one or more blockchains or changes to make to existing data in the one or more blockchains; and updating the plurality of pieces of data stored in the one or more blockchains, comprising: obtaining one or more blockchain addresses associated with the one or more local accounts and one or more private keys correspondingly associated with the one or more blockchain addresses; correspondingly updating the one or more unsigned blockchain transactions based on the one or more blockchain addresses; correspondingly signing the one or more updated blockchain transactions with the one or more private keys; and transmitting the signed one or more blockchain transactions to one or more blockchain nodes of the one or more blockchains for execution; wherein the one or more blockchain addresses associated with the one or more local accounts and the one or more private keys associated with the one or more blockchain addresses are stored in the server end and not at the client. obtaining (511, 521), from a client, one or more requests for updating data in one or more blockchains, comprising obtaining one or more local accounts associated with one or more users of the client, one or more unsigned blockchain transactions to be executed for correspondingly updating a plurality of pieces of data stored in the one or more blockchains and associated with the one or more local accounts, information of the plurality of pieces of data for updating the plurality of pieces of data, and one or more identifications of the one or more blockchains corresponding to the one or more blockchain transactions, wherein the information of the plurality of pieces of data comprises new data to add to the one or more blockchains or changes to make to existing data in the one or more blockchains; and updating the plurality of pieces of data stored in the one or more blockchains, comprising: obtaining one or more blockchain addresses associated with the one or more local accounts and one or more private keys correspondingly associated with the one or more blockchain addresses; correspondingly updating the one or more unsigned blockchain transactions based on the one or more blockchain addresses; correspondingly signing the one or more updated blockchain transactions with the one or more private keys; and transmitting the signed one or more blockchain transactions to one or more blockchain nodes of the one or more blockchains for execution; wherein the one or more blockchain addresses associated with the one or more local accounts and the one or more private keys associated with the one or more blockchain addresses are stored in the server end and not at the client. obtaining one or more blockchain addresses associated with the one or more local accounts and one or more private keys correspondingly associated with the one or more blockchain addresses; correspondingly updating the one or more unsigned blockchain transactions based on the one or more blockchain addresses; correspondingly signing the one or more updated blockchain transactions with the one or more private keys; and transmitting the signed one or more blockchain transactions to one or more blockchain nodes of the one or more blockchains for execution; wherein the one or more blockchain addresses associated with the one or more local accounts and the one or more private keys associated with the one or more blockchain addresses are stored in the server end and not at the client.