Integrity Measurement Architecture

The Linux Integrity Measurement Architecture (IMA) maintains a runtime measurement list and, if anchored in a hardware Trusted Platform Module (TPM), an aggregate integrity value over this list. The benefit of anchoring the aggregate integrity value in the TPM is that the measurement list cannot be compromised by any software attack without being detectable. Hence on a trusted boot system, IMA can be used to attest the system’s runtime integrity.

strongTNC IMA Database

TPM BIOS/IMA Measurements and SW ID Subscription Policy

In order to enable BIOS and IMA measurements, add the TPM BIOS/IMA group in the Device Info menu for a given device.

Assignment of Group Memeberships
Figure 1. Assignment of Group Memberships

Since IMA measurements needs current file reference hashes, the SW ID Subscription Policy is added via a special PT-TLS group.

Assignment of Group Memeberships
Figure 2. Add SW ID Subscription Policy to PT-TLS Gropu

Additionally set the Trusted flag in order to put trust into the Attestation Key sent by the endpoint via the PA-TNC protocol. The Device ID is the keyid of the AK, so that the correctness of the public key can be verified.

Device Report

The session details of the device report show that 26 SW ID events, 1732 IMA measurements and 136 BIOS measurements were received and successfully verified.

SW ID Events and BIOS/IMA Measurements
Figure 3. Session Details showing SW ID Events and BIOS/IMA Measurements

TPM Evidence

The TPM Evidence consists of 136 BIOS Measurements extended to PCR registers 0..9 and 14

Top of TPM Evidence Entries
Figure 4. Top of TPM Evidence Entries

At the very end of the evidence list is the boot aggregate (SHA256 hash of the concatenated SHA256 hashes of the final state of PCRs 0..9 which is the first value that is extended into PCR 10)

Tail of TPM Evidence Entries
Figure 5. Tail of TPM Evidence Entries

IMA Client

The IMA Client is the TNC component located on the client side, retrieving and transmitting the TPM BIOS and IMA evidence measurements and updating the file hashes via the collector.db database.

IMA Server

The IMA Server is the TNC component running on the server side, receiving the TPM BIOS evidence measurements and storing or verifying them in the strongTNC database. The received IMA evidence measurements are compared with the reference file hashes stored in the strongTNC database that are periodically updated.