origin and authenticity of a trust measurement, but also to authenticate other keys generated by the TPM. Before an AIK can testify the authenticity of any data, a PCA has to issue a credential for it. This credential together with the AIK can therefore be used as an identity for this platform. The protocol for issuing this credential consists in three basic steps. First, the TPM generates an RSA key pair by performing the `TPM_MakeIdentity` command. The resulting public key together with certain credentials identifying the platform is then transferred to the PCA. Second, the PCA verifies the correctness of the produced credentials and the AIK signature. If they are valid the PCA creates the AIK credential which contains an identity label, the AIK public key, and information about the TPM and the platform. A special structure containing the AIK credential is created which is used in step three to activate the AIK by executing the `TPM_ActivateIdentity` command. So far, the TCG-specified protocol is not completely secure, since between steps two and three, some kind of handshake between PCA and platform is missing. The existing protocol could sensibly be enhanced by a challenge/response part to verify the link between the 