# US 9,520,993 B2 · Renewable traitor tracing > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,520,993 B2 - Document ID: US9520993B2 - Status: Granted - Kind: B2 - Application number: 11/230,022 - Filed: 2005-09-19 - Published: 2007-03-22 - Granted: 2016-12-13 - Earliest claimed: 2005-09-19 - Assignees: International Business Machines Corporation - Applicants: Hongxia Jin; Jeffrey Bruce Lotspiech; Sigfredo Ismael Nin - Inventors: Hongxia Jin; Jeffrey Bruce Lotspiech; Sigfredo Ismael Nin - Web page: https://patentgrep.com/patent/US9520993B2 ## CPC - H04L 9/3268: {using certificate validation, registration, distribution or revocation, e.g. certificate revocation list [CRL]} - H04L 9/083: {involving central third party, e.g. key distribution center [KDC] or trusted third party [TTP]} - H04L 9/0891: {Revocation or update of secret information, e.g. encryption key update or rekeying} - H04L 9/3247: {involving digital signatures} - H04L 63/061: {for key exchange, e.g. in peer-to-peer networks (cryptographic mechanisms or cryptographic arrangements for key agreement H04L9/0838)} - H04L 2209/601: Broadcast encryption - H04L 2209/606: Traitor tracing - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract The present invention provides a method performed on a computer of preventing re-use of compromised keys in a broadcast encryption system. In an exemplary embodiment, the method includes (1) incorporating a particular set of Sequence Keys assigned by a license agency into individual receivers, (2) assigning a Sequence Key Block (SKB) by the license agency to at least one distributed protected file, (3) performing incremental cryptographic testing by the individual receivers to determine if a selected Sequence Key from the set of Sequence Keys is compromised, (4) if the selected Sequence Key is not compromised, decrypting the file, and (5) if the selected Sequence Key is compromised and if a subsequent Sequence Key from the set of Sequence Keys is available, selecting the subsequent Sequence Key. ## Claims ### Claim 1 A method of preventing re-use of compromised sequence keys in a broadcast encryption system, the method comprising: receiving a distributed protected file and a sequence key block at a receiver, the sequence key block being formulated to cryptographically revoke traitorous receivers; selecting a first Sequence Key from a plurality of Sequence Keys, the plurality of Sequence Keys being associated with the receiver, and the plurality of Sequence Keys being related by the sequence key block; determining by cryptographic testing that the first Sequence Key is compromised, cryptographic testing comprising applying the first Sequence Key to the sequence key block; determining that at least one additional Sequence Key is available; traversing the sequence key block to select a second Sequence Key from the plurality of sequence keys; determining by cryptographic testing that the second sequence key is compromised, cryptographic testing comprising applying the first Sequence Key to the sequence key block; traversing the remainder of the sequence key block and thereby determining that no uncompromised sequence keys can be determined from the sequence key block; identifying the receiver as traitorous based on the lack of uncompromised sequence keys. ### Claim 2 (depends on 1) The method of claim 1, wherein the distributed protected file includes digital forms of at least one of: a cryptographic key, text, audio, an image, video, a multimedia presentation, music, a movie, an operating system, a video game, play instructions that select segments according to an inner codeword, and a software application. ### Claim 3 (depends on 1) The method of claim 1, wherein the distributed protected file is distributed by at least one of: computer networks, satellite networks, cable networks, television transmission, and physical storage media. ### Claim 4 (depends on 1) The method of claim 1, wherein the plurality of Sequence Keys is related by a linked list. ### Claim 5 (depends on 1) The method of claim 1, wherein the cryptographic testing of the first sequence key comprises: determining that a Link Key is available; cryptographically applying the first Sequence Key and the Link Key to the Sequence Key Block to obtain a predetermined value indicating whether the first Sequence Key is compromised. ### Claim 6 (depends on 5) The method of claim 5, further comprising: generating a Link Key leading to the second Sequence Key. ### Claim 7 A computer program product for preventing re-use of compromised sequence keys in a broadcast encryption system, the computer program product comprising a non-transitory computer readable storage medium having computer readable program code embodied therewith, the computer readable program code comprising computer readable code for: receiving a distributed protected file and a sequence key block at a receiver, the sequence key block being formulated to cryptographically revoke traitorous receivers; selecting a first Sequence Key from a plurality of Sequence Keys, the plurality of Sequence Keys being associated with the receiver, and the plurality of Sequence Keys being related by the sequence key block; determining by cryptographic testing that the first Sequence Key is compromised, cryptographic testing comprising applying the first Sequence Key to the sequence key block; determining that at least one additional Sequence Key is available; traversing the sequence key block to select a second Sequence Key from the plurality of sequence keys; determining by cryptographic testing that the second sequence key is compromised, cryptographic testing comprising applying the first Sequence Key to the sequence key block; traversing the remainder of the sequence key block and thereby determining that no uncompromised sequence keys can be determined from the sequence key block identifying the receiver as traitorous based on the lack of uncompromised sequence keys. ### Claim 8 (depends on 7) The computer program product of claim 7, wherein the distributed protected file includes digital forms of at least one of: a cryptographic key, text, audio, an image, video, a multimedia presentation, music, a movie, an operating system, a video game, play instructions that select segments according to an inner codeword, and a software application. ### Claim 9 (depends on 7) The computer program product of claim 7, wherein the distributed protected file is distributed by at least one of: computer networks, satellite networks, cable networks, television transmission, and physical storage media. ### Claim 10 (depends on 7) The computer program product of claim 7, wherein the plurality of Sequence Keys is related by a linked list. ### Claim 11 (depends on 7) The computer program product of claim 7, wherein the cryptographic testing of the first sequence key comprises: determining that a Link Key is available; cryptographically applying the first Sequence Key and the Link Key to the Sequence Key Block to obtain a predetermined value indicating whether the first Sequence Key is compromised. ### Claim 12 (depends on 11) The computer program product of claim 11, further comprising: generating a Link Key leading to the second Sequence Key. ### Claim 13 (depends on 1) The method of claim 1, wherein traversing the sequence key block comprises: obtaining a link key based on the first sequence key; and determining the second sequence key based on the link key. ### Claim 14 (depends on 7) The computer program product of claim 7, wherein traversing the sequence key block comprises: obtaining a link key based on the first sequence key; and determining the second sequence key based on the link key. ### Claim 15 (depends on 1) The method of claim 1, wherein traversing the remainder of the sequence key block comprises: obtaining a link key based on the second sequence key. ### Claim 16 (depends on 7) The computer program product of claim 7, wherein traversing the remainder of the sequence key block comprises: obtaining a link key based on the second sequence key. ### Claim 17 (depends on 7) The method of claim 7, further comprising: disabling the receiver as traitorous. ### Claim 18 (depends on 7) The computer program product of claim 7, the computer readable program code further comprising computer readable code for: disabling the receiver as traitorous. ### Claim 19 (depends on 7) The method of claim 7, further comprising: revoking the plurality of sequence keys. ### Claim 20 (depends on 7) The computer program product of claim 7, the computer readable program code further comprising computer readable code for: evoking the plurality of sequence keys.