| US 7,590,240 B2 | ||
| Conditional access system and method prevention of replay attacks | ||
| David C. Platt, Mountain View, Calif. (US); Andrew Goodman, Menlo Park, Calif. (US); and Daniel Zenchelsky, Los Gatos, Calif. (US) | ||
| Assigned to TiVo Inc., Alviso, Calif. (US) | ||
| Appl. No. 10/220,356 PCT Filed Mar. 02, 2001, PCT No. PCT/US01/06911 § 371(c)(1), (2), (4) Date Dec. 11, 2002, PCT Pub. No. WO01/65762, PCT Pub. Date Sep. 07, 2001. |
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| Prior Publication US 2004/0126093 A1, Jul. 01, 2004 | ||
| Int. Cl. H04N 7/167 (2006.01) | ||
| U.S. Cl. 380—210 | 30 Claims |
| 1. A cryptographic method for rendering a conditional access system resistant to replay attacks comprising the steps of:
generating a set of one or more keys usable for encryption or decryption, said generating caused by an authorization module
controlling authorization of access to a plurality of transport streams, said authorization module on or in communication
with a receiver among a plurality of receivers in communication with a headend;
storing an encrypted transport stream transmitted from said headend, wherein said encrypted transport stream is further encrypted
at said receiver, using one or more keys from said set of one or more keys usable for encryption or decryption, so that a
doubly encrypted transport stream is stored on a storage medium on or accessible to said receiver; and
decrypting said doubly encrypted transport stream by a decryption module on or in communication with said receiver using one
or more keys from said set of one or more keys usable for encryption or decryption.
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