Protection of control words employed by conditional access systems

1. A method for providing secure transmission of video, wherein the transmission provides for communicating a control word (CW) to a server associated with a conditional access system (CAS), comprising:

establishing communication between a client and the server over a secure connection to transmit the video;

receiving at the client a control word to be encrypted;

encrypting at the client the control word using a first and second key, the first key being a global secret key (GSK) that is known to the client and the server without being communicated over the secure connection, the second key being a control word encryption key (CWEK) that is derived from a locally generated client nonce (CN) and a server nonce (SN) obtained from the server over the secure connection; and

sending the encrypted control word (ECW) to the server over the secure connection,

wherein the client is a SimulCrypt Synchronizer (SCS) and the server is an entitlement control message generator (ECMG) that generates entitlement control message (ECMs) using the control words received from the SCS.

2. A method for providing secure transmission of video, wherein the transmission provides for communicating a control word (CW) to a server associated with a conditional access system (CAS), comprising:

establishing communication between a client and the server over a secure connection to transmit the video;

receiving at the client a control word to be encrypted;

sending a list of global secret key (GSK) identifiers to the server over the secure connection, each of the GSK identifiers identifying a different GSK; and

receiving a selected GSK identifier over the secure connection, the selected GSK identifier identifying a selected GSK that is used as a first key

encrypting at the client the control word using the first key and a second key, the first key being one of the GSKs that is known to the client and the server without being communicated over the secure connection, the second key being a control word encryption key (CWEK) that is derived from a locally generated client nonce (CN) and a server nonce (SN) obtained from the server over the secure connection; and

sending the encrypted control word (ECW) to the server over the secure connection.

3. A method for providing secure transmission of video, wherein the transmission provides for communicating a control word (CW) to a server associated with a conditional access system (CAS), comprising:

establishing communication between a client and the server over a secure connection to transmit the video, wherein the server is one of a plurality of load-balancing servers associated with the CAS;

receiving an encrypted control word encryption nonce (CWEN) from the server over the secure connection, the CWEN being derived from a locally generated client nonce (CN) and a server nonce SN;

encrypting at the client the control word using a first key and a second key, the first key being one of the GSKs that is known to the client and the server without being communicated over the secure connection, the second key being a control word encryption key (CWEK) that is derived from the CN and the SN;

sending the encrypted control word (ECW) to the server over the secure connection;

encrypting the CWEN using a key associated with the server, the encrypted CWEN being available to and decryptable by the plurality of servers;

sending the encrypted CWEN to the server along with the encrypted control word.

4. The method of claim 3 , wherein the CWEN is derived by combining the CN and the SN.

5. The method of claim 2 , wherein each of the GSKs is maintained in a secure hardware module associated with the client and further comprising accessing the selected GSK from the secure hardware module.

6. The method of claim 1 , further comprising sending an ECM request to the ECM generator over the secure connection, the ECM request including the encrypted control word.

7. The method of claim 1 , wherein establishing communication between the client and the server over the secure connection includes authenticating the SCS using a digital certificate issued by a certificate authority associated with the CAS.

8. The method of claim 7 , wherein the secure connection conforms to a Transport Layer Security (TLS) protocol.

9. The method of claim 1 , further comprising:

deriving a control word authentication key (CWAK) from the locally generated CN and the SN;

generating a control word authenticator (CWA) using the ECW and the CWAK; and

sending the CWA to the server for use in authenticating the CW.

10. One or more non-transitory computer-readable storage media containing instructions which, when executed by one or more processors allow secure transmission of video, wherein the processor accomplishes the transmission performing a method comprising:

receiving a client nonce (CN) from a client associated with an encryption engine over a secure connection between the client and a server associated with a conditional access system (CAS);

sending a server nonce (SN) from the server to the client over the secure connection;

deriving a control word encryption key (CWEK) for use in encrypting and decrypting a control word, the CWEK being derived using the client nonce (CN) and the server nonce (SN);

receiving a list of global secret key (GSK) identifiers over the secure connection, each of the GSK identifiers identifying a different GSK;

selecting a GSK identifier, the selected GSK identifier identifying a selected GSK that is used by the client to encrypt the control word;

sending the selected GSK identifier to the client;

receiving from the client a request for receipt of an entitlement control message (ECM), the request including the control word in encrypted form using the CWEK and an identified one of the global secret keys (GSK) that is known to the client and the server without being communicated over the secure connection;

decrypting the encrypted control word using the GSK and the CWEK; and

generating an ECM that includes the control word; and sending the ECM to the client over the secure connection.

11. The one or more computer-readable storage media of claim 10 , further comprising:

deriving a control word authentication key (CWAK) for use in authenticating the control word, the CWAK being derived using the CN and the SN;

deriving a control word authentication (CWA) using the encrypted control word and the CWAK;

comparing the derived CWA to a CWA received from the client; and

authenticating the control word if the derived CWA matches the CWA received from the client.

12. The one or more computer-readable storage media of claim 10 , further comprising:

deriving a control word encryption nonce (CWEN) using the CN and SN;

encrypting the CWEN with a private key associated with the server; and

sending the encrypted CWEN (ECWEN) to the client.

13. The one or more computer-readable storage media of claim 12 , wherein the server is one of a plurality of load-balancing servers associated with a CAS, the ECWEN being available to and decryptable by the plurality of servers, and further comprising:

receiving the ECWEN from the client along with the encrypted control word; and

obtaining the CWEK by identifying a cached CWEK corresponding to the received ECWEN.

14. The one or more computer-readable storage media of claim 12 , wherein deriving the CWEN further comprises combining the CN and SN to form the CWEN.

15. The one or more computer-readable storage media of claim 10 , further comprising accessing the GSK from a secure hardware module associated with the server.

16. The one or more computer-readable storage media of claim 10 , wherein the server is an ECM generator associated with the CAS.

17. The one or more computer-readable storage media of claim 16 , further comprising establishing communication between the client and the ECM generator over the secure connection, wherein establishing communication includes authenticating the client using a digital certificate issued by a certificate authority associated with the CAS.

18. The one or more computer-readable storage media of claim 10 , wherein the secure connection conforms to a Transport Layer Security (TLS) protocol.