1. An apparatus for online signature verification analyzing a reference signature database (DB) of a specific user, the apparatus comprising: a signature data input unit for digitalizing a locus of a user signature and reading the digitized locus as a sequence of points sampled at regular time intervals; a first pattern transform unit for performing a speed equalization on the signature sequence read by the signature data input unit and generating a first transformed pattern sequence; a second pattern transform unit for performing a velocity transform on the signature sequence read by the signature data input unit and generating a second transformed pattern sequence; a feature extraction unit for extracting three feature vectors from the signature sequence read by the signature data input unit, the first pattern sequence transformed by the first pattern transform unit and the second pattern sequence transformed by the second pattern transform unit, respectively, to thereby generate the three feature vectors having different information; a difference vector estimation unit for generating a difference vector between the feature vector of the specific user's reference signature read from the reference DB and the feature vector extracted by the feature extraction unit; and a determination unit for determining whether an input signature and the reference signature are signed by a single person, based on the difference vector generated from the difference vector estimation unit.