There is described an authentication system in which during an enrolment process a distinctive characteristic of a subject being enrolled is measured to generate a reference number representative of the subject. Authentication data is then generated using the reference number, and the authentication data is stored for use in a subsequent verification process. During verification, the representative characteristic of the subject being verified is re-measured to generate a test number representative of the subject being verified and the authentication data during enrolment is retrieved. The authentication system then checks for equality between the test number and the reference number using the retrieved authentication data. If the test number and the reference number are equal, then the authenticity of the subject is verified, otherwise the authenticity is denied.