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Integrity Measurement Architecture

Integrity Measurement Architecture (IMA) is a classic static remote attestation model developed by IBM[1] for measurement and reporting of the integrity of Linux-based systems. It takes a hash of the binaries of the software code that run on any system, and compares them against known-good hashes to assert that the system is high integrity. IMA extends the trusted boot process of the TCG beyond the bootstrapping of the Linux loader, to the chain of trust from the TPM, to applications running on the system. Through extensions to the kernel of the Linux system, IMA measures the code that's loaded into memory for execution by taking a SHA-1 hash of the code prior to that execution. A measurement archive is maintained for measurements previously taken.

Integrity Measurement Architecture was the first practical implementation of a TCG-based remote attestation technique. It allows a challenger to verify a platform status by measuring the executables running on that platform. IMA forms the basis for many remote attestation techniques that followed the original implementation. The requirement for using IMA is to download a kernel patch from IBM. The prototype of IMA was implemented as a Linux Security Module on RedHat 9.0 Linux distribution and kernel version 2.6.5.

Policy Reduced Integrity Measurement Architecture

Policy Reduced Integrity Measurement Architecture (PRIMA) is a variation of IMA. According to the authors of this architecture,

[2] the static code and load-time measurement cannot be used to assess the run-time behavior. This architecture introduces the concept of measured security context or label of the subject, in addition to static code. The code/ data digest also includes a role field so that additional identification of subjects and objects can be done. This approach allows remote attestation to be made on the basis of secure information-flow models. The approach is rather low level and cannot be used for distributed services in an organization or the information flows that occur within the organization and in outside world. There are no known implementations in a commonly available operating system environment.

Semantic Remote Attestation

Semantic Remote Attestation is an attempt at creating a platform-independent remote attestation technique.[3] The core idea is that of a trusted virtual machine (TVM) capable of enforcing the requirements for those applications running within this virtual machine. The model establishes trust on the TVM and uses this trust to enforce security requirements. It attempts to measure the behavior of the code running inside a trusted virtual machine. The architecture is an incremental improvement over the original remote attestation techniques and is more flexible compared with binary attestation techniques with regard to expressiveness. This model of attestation has not been implemented, or at least published, owing to the complexity of defining and analyzing the notion of trust.

  • [1] See researcher.watson.ibm.com/researcher/files/us-msteiner/ima.sailer_ usenix_security_2004_slides.pdf
  • [2] Trent Jaeger et al., “PRIMA: PolicyReduced Integrity Measurement Architecture, SACMAT2006,

    June 7–9, 2006, Lake Tahoe, California. ACM 1595933549/06/0006

  • [3] Vivek Haldar et al., Semantic Remote Attestation: a Virtual Machine Directed Approach to Trusted Computing, VM2004 Proceedings of the 3rd conference on Virtual Machine Research and Technology Symposium, vol. 3 (Berkeley, CA: USENIX Association)
 
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