A biometric-based security circuit in which the user database, processor, and biometric map generation functions are all located on the same integrated circuit whose secure contents are inaccessible from external to the integrated circuit. Biometric data, such as a fingerprint, retina scan, or voiceprint, is taken from a user requesting access to restricted resources. The biometric data is transferred into the integrated circuit, where it is converted to a biometric map and compared with a database of biometric maps stored in a non-volatile memory in the integrated circuit. The stored maps represent pre-authorized users, and a match triggers the security circuit to send a signal to a host processor authorizing the host processor to permit the requesting user access to the restricted resources. The integrated circuit essentially serves as a write-only memory for the secure data, because the secure data and security functions in the integrated circuit are not directly accessible through any pin or port, and therefore cannot be read or monitored through a dedicated security attack. A second non-volatile memory, accessible from external to the integrated circuit, can also be provided in the integrated circuit for holding non-secure data. This second memory has its own interface port, and is isolated from the security-related functions and memory so that secure and non-secure functions are physically isolated from each other and cannot be modified to overcome that isolation.