Revocation of TPM Keys
A Trusted Platform Module (TPM) offers a number of basic security services which can be used to build complex trusted applications. One of the main functionalities of a TPM is the provision of a protected storage, including access management for cryptographic keys. To allow for scalability in spite of the resource constraints of the TPM, keys are not stored inside the TPM, but in encrypted form on external, untrusted storage. This has the consequence that the actual key storage is not under control of the TPM, and it is therefore not possible to revoke individual keys. In this paper we introduce two basic methods to implement key revocation without major changes to the TPM command set, and without inhibiting backwards compatibility with the current specification. Our methods introduce no overhead for normal operation, and a reasonable small effort for managing revocable keys.
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