An identity authentication method is provided. The method comprises obtaining records information of a valid user, where the records information indicates behaviors having been executed by the valid user; mapping, based on an orthogonal behavior model having multiple mutually orthogonal dimensions, records information to the multiple dimensions, wherein behaviors indicated by records information mapped to different dimensions do not overlap therebetween and have no logical cause and effect relationship; sampling records information mapped to different dimensions, respectively, so as to generate an authentication questionnaire including a plurality of authentication questions; computing, responsive to answers of a client to the authentication questionnaire, a total confidence P for the client being a valid user; outputting a positive authentication result, responsive to the total confidence probability P falling into a confidence interval; and outputting a negative authentication result, responsive to the total confidence probability P failing to fall into a confidence interval. The present invention further provides a corresponding identity authentication apparatus.