METHOD AND APPARATUS FOR EMBEDDING SECRET INFORMATION IN DIGITAL CERTIFICATES
A method and system is provided for embedding cryptographically modified versions of secret in digital certificates for use in authenticating devices and in providing services subject to conditional access conditions.
1 . A method of enabling provision of a service to a first entity, comprising the steps of:
receiving a service request in a second entity from the first entity, the service request comprising a leaf digital certificate generated and digitally signed by a certification entity and provided to the first entity, the leaf digital certificate having a unique identifier of the first entity and a two-way cryptographic function of a secret generated according to a provision key unknown to the first entity and the digital certificate digitally signed by a private key of the certification entity according to an asymmetric crypto algorithm;
recovering the secret in the second entity from the leaf digital certificate; and
enabling provision of the service to the first entity according to the recovered secret.
2 . The method of claim 1 , wherein the step of recovering the secret comprises:
recovering the two-way cryptographic function of the secret from the digitally signed digital certificate; and
inverting the two-way cryptographic function to recover the secret.
3 . The method of claim 2 , wherein the step of inverting the two way cryptographic function comprises:
inverting the two-way cryptographic function according to the provision key.
4 . The method of claim 3 , wherein the two-way cryptographic function is a symmetric function and the provision key is a symmetric key known to the certification entity and the service enabling entity.
5 . The method of claim 3 , wherein the two-way cryptographic function is an asymmetric function and the provision key is an encryption key and the two-way cryptographic function is inverted according to a decryption key corresponding to the encryption key.
6 . The method of claim 2 , wherein the step of recovering the two-way cryptographic function of the secret from the digital certificate comprises:
attempting verifying the digitally signed leaf digital certificate; and
recovering the two way cryptographic function of the secret from the leaf digital certificate only if the leaf digital certificate is verified.
7 . The method of claim 6 , wherein the leaf digital certificate is verified according to a public key of the certification entity.
8 . The method of claim 6 , wherein:
the first entity is a member of a class of devices, and the certification entity comprises a sub-certification entity providing the leaf digital certificate to the first entity and other leaf digital certificates to each of the other devices in the class of devices;
each leaf digital certificate comprises a unique identifier of each associated device and an associated secret unique to the associated device;
each leaf digital certificate is digitally signed according to a trusted sub-certification entity digital certificate provided by the sub-certification entity; and
the method further comprises:
determining if the sub-certification entity certificate or any digital certificate in a chain up to a root of trust has been revoked; and
verifying the leaf digital certificate only if the trusted digital sub-certification entity digital certificate and any digital certificate in the chain up to the root of trust has not been revoked.
9 . The method of claim 8 , wherein the step of determining if the trusted sub-certificate has been revoked comprises:
receiving, from the second entity, a list identifying revoked sub-certification entity certificates; and
determining that the trusted sub-certification entity certificate has been revoked if the list identifies the trusted sub-certification entity certificate.
10 . The method of claim 1 , wherein the certification entity further provides the secret to the first entity and the provision of the service is enabled at least in part on a match between the secret provided to the first entity and the secret recovered by the second entity.
11 . The method of claim 10 , wherein the secret is provided to the first entity in a same message as the digital certificate.
12 . The method of claim 1 , wherein the provision of the service is enabled only if the digital certificate and all digital certificates in the chain from the digital certificate up to a root of trust are not a member of a set of revoked digital certificates.
13 . The method of claim 12 , further comprising the steps of:
receiving, in the second entity, a list identifying revoked digital certificates; and
determining if the digital certificate is among the identified the revoked digital certificates;
enabling the provision of the service only if the digital certificate and all digital certificates in the chain from the digital certificate up to a root of trust are not among the identified revoked digital certificates.
14 . An apparatus for enabling provision of a service to a first entity the apparatus disposed in a second entity and comprising:
a communications module, for transceiving information, wherein the information comprises:
a service request from the first entity, the service request comprising a leaf digital certificate generated and digitally signed by a certification entity and provided to the first entity, the leaf digital certificate having a unique identifier of the first entity and a two-way cryptographic function of a secret generated according to a provision key unknown to the first entity and the digital certificate digitally signed by a private key of the certification entity according to an asymmetric crypto algorithm;
a processor, for executing instructions stored in a memory communicatively coupled to the processor, the instructions including instructions for:
recovering the secret in the second entity from the leaf digital certificate; and
enabling provision of the service to the first entity according to the recovered secret.
15 . The apparatus of claim 14 , wherein the instructions for recovering the secret comprise instructions for:
recovering the two-way cryptographic function of the secret from the digitally signed digital certificate; and
inverting the two-way cryptographic function to recover the secret.
16 . The apparatus of claim 15 , wherein:
the instructions for inverting the two way cryptographic function comprise instructions for inverting the two-way cryptographic function according to the provision key;
17 . The apparatus of claim 16 , wherein the two-way cryptographic function is a symmetric function and the provision key is a symmetric key known to the certification entity and the service enabling entity.
18 . The apparatus of claim 16 , wherein the two-way cryptographic function is an asymmetric function and the provision key is an encryption key and the two-way cryptographic function is inverted according to a decryption key corresponding to the encryption key.
19 . The apparatus of claim 15 , wherein the instructions recovering the two-way cryptographic function of the secret from the digital certificate comprise instructions for:
attempting verifying the digitally signed leaf digital certificate; and
recovering the two way cryptographic function of the secret from the leaf digital certificate only if the leaf digital certificate is verified.
20 . The apparatus of claim 19 , wherein:
the first entity is a member of a class of devices, and the certification entity comprises a sub-certification entity providing the leaf digital certificate to the first entity and other leaf digital certificates to each of the other devices in the class of devices;
each leaf digital certificate comprises a unique identifier of each associated device and an associated secret unique to the associated device;
each leaf digital certificate is digitally signed according to a trusted sub-certification entity digital certificate provided by the sub-certification entity; and
the instructions further comprise instructions for:
determining if the sub-certification entity certificate or any digital certificate in a chain up to a root of trust has been revoked; and
verifying the leaf digital certificate only if the trusted digital sub-certification entity digital certificate and any digital certificate in the chain up to the root of trust has not been revoked.