Electronic signature management system

Abstract

An electronic signature management system includes a graphic tablet digitizer for signaling position coordinates of a stylus being moved to produce a handwritten signature, a clock circuit of the digitizer defining a fixed interval between successive stylus position measurements, a computer processor electrically interfaced with the tablet and programmed for receiving and storing a multiplicity of the coordinates in sequential order as an electronic signature forming a time history of the stylus movement. The computer is also programmed for verifying the fixed time intervals of the measurements, such as by comparing a ratio of total elapsed time and total number of the measurements with a standard measurement interval, and for comparing the electronic signature with a reference signature, such as by feeding a stored reference signature counterpart and the electronic signature into a cross-correlator for evaluating a degree of correspondence between respective time histories of the electronic signature and the reference signature. The signatures can also be compared visually in a simultaneous display wherein respective pointers follow the signatures orthogonally in response to an operator-controlled slider, with pertinent data corresponding to the pointer positions being displayed. The electronic signature is preferably encrypted using a hash function or message digest of the document as a key. Also disclosed are methods for electronically signing a document, wherein the electronic signature is electronically bound to the document, wherein the electronic signature is encrypted using a key derived from the document and not saved, and methods for decrypting and verifying electronic signatures.