Algorithm agility – discussion on TPM 2.0 ECC functionalities

Abstract

The TPM 2.0 specification has been designed to support a number of Elliptic Curve Cryptographic (ECC) primitives, such as key exchange, digital signatures and Direct Anonymous Attestation (DAA). In order to meet the requirement that different TPM users may favor different cryptographic algorithms, each primitive can be implemented from multiple algorithms. This feature is called Algorithm Agility. For the purpose of performance efficiency, multiple algorithms share a small set of TPM commands. In this paper, we review all the TPM 2.0 ECC functionalities, and discuss on whether the existing TPM commands can be used to implement new cryptographic algorithms which have not yet been addressed in the specification. We demonstrate that four asymmetric encryption schemes specified in ISO/IEC 18033-2 can be implemented using a TPM 2.0 chip, and we also show on some ECDSA variants that the coverage of algorithm agility from TPM 2.0 is limited. Security analysis of algorithm agility is a challenge, which is not responded in this paper. However, we believe that this paper will help future researchers analyze TPM 2.0 in more comprehensive methods than it has been done so far.