Abstract: A system for signing transactions. The system includes a first module with a communication interface to a public network; and a controller to handle a transaction with a Blockchain network or a transaction server accessible at the public network. The system also includes a second module with a random number generator; and a secure controller to generate seed words and private keys. The system further includes a bridge module with a controller; and a switch to selectively connect the data interface of the bridge module to either the data interface of the first module or the data interface of the second module such that the data interface of the first module is never connected with the data interface of the second module.