Patent ID: 9667428
Date: 2017-05-30
CPC Classifications: H04L

Claim:
1. A user computer configured to produce a cryptographic signature on a message under a key which is shared between the user computer and an authentication computer, wherein the authentication computer stores a second key-share and a first authentication value which encodes a secret value of the user computer and a predetermined user password, the user computer comprising memory configured to store a first key-share, a user interface, a communications interface configured to communicate with the authentication computer, and control logic configured to: in response to provision of the message and input, via said user interface, of said user password, to encode the message to produce a blinded message, to produce said first authentication value from the user password and said secret value and produce a second authentication value which encodes the first authentication value and a nonce, and to send the second authentication value and the blinded message to the authentication computer via said communications interface; and in response to receipt from the authentication computer of a partial signature produced by encoding the blinded message using the second key-share, to produce a signature on the message under said key by encoding the partial signature and the message using the first key-share and an unblinding function configured to unblind the blinded message in the partial signature.