| Number | Name | Date | Kind |
|---|---|---|---|
| 5319562 | Whitehouse | Jun 1994 | A |
| 5511121 | Yacobi | Apr 1996 | A |
| 5606613 | Lee et al. | Feb 1997 | A |
| 5812991 | Kara | Sep 1998 | A |
| 5872844 | Yacobi | Feb 1999 | A |
| 5936221 | Corder et al. | Aug 1999 | A |
| 6005945 | Whitehouse | Dec 1999 | A |
| 6424954 | Leon | Jul 2002 | B1 |
| 20020146122 | Vestergaard et al. | Oct 2002 | A1 |
| Number | Date | Country |
|---|---|---|
| WO 99343311 | Aug 1999 | AU |
| Entry |
|---|
| Chaum, David Achieving electronic privacy, Internet, Aug. 1992 pp. 1-8. |