Multiparty computation for approving digital transaction by utilizing groups of key shares

A method for securing a digital transaction operable by a multiparty signing server communicating with a coordinator, wherein the multiparty signing server is connected to a first subset of end-user nodes and the coordinator is connected to a second subset of end-user nodes thereby forming an approving subsystem, comprising:

• receiving a transaction to sign by the multiparty signing server, wherein the transaction to sign is received from a third-party server;
• sending by the multiparty signing server a first request to receive a first group of key shares, wherein said first request is sent to a coordinator;
• sending by the coordinator a second request to receive the first group of key shares, wherein the second request is sent to the second subset of the end-user nodes;
• receiving the first group of key shares by the coordinator, wherein the first group of key shares is sent by the second subset of the end-user nodes;
• sending the received first group of key shares by the coordinator, to the multiparty signing server;
• conducting a multiparty computation (MPC) process by the multiparty signing server to generate a signature, wherein the MPC process is conducted between the multiparty signing server and the to the first subset of the end-user nodes, by using the received first group of key shares and a second group of key shares held by the first subset of the end-user nodes;
• receiving by the multiparty signing server the signature on the transaction as a result of the MPC process;
• and
• sending the signed transaction to the third-party server,
• wherein the second subset of the end-user nodes which are connected to the approving subsystem are connected off-line such that the end-user nodes are configured to guarantee to be connected to receive a single message or send a single message but are not synchronized nor connected to each other at the same time, during the MPC process.