Sealed messages show that the contents have not been accidentally or intentionally changed. Sealing is normally done using a checksum, which is appended to the message or sent separately. A checksum is the result of a calculation which uses data from the message. To check that the message has not been altered, the checksum is recalculated. If the data used in the calculation have been changed, then the result is different, indicating that the seal has been broken.
Most seals use encryption to increase the security of the checksum.
Smart cards are plastic cards which look like credit cards and contain a microchip memory instead of a magnetic strip. A smart card s microprocessor can check that the device reading the card is authorized to do so. However, they are only marginally more secure than traditional storage media, such as magnetic tape. Biometric techniques use unique human attributes to provide high levels of assurance identity and authentication. These attributes include finger prints, voice recognition, and handshape.