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Intel SGX promises powerful security: an arbitrary number of user-mode enclaves protected against physical attacks and privileged software adversaries. However, to achieve this, Intel extended the x86 architecture with an isolation mechanism approaching the complexity of an OS microkernel, implemented by an inscrutable mix of silicon and microcode. While hardware-based security can offer performance and features that are difficult or impossible to achieve in pure software, hardware-only solutions are difficult to update, either to patch security flaws or introduce new features. Komodo illustrates an alternative approach to attested, on-demand, user-mode, concurrent isolated execution. We decouple the core hardware mechanisms such as memory encryption, address-space isolation and attestation from the management thereof, which Komodo delegates to a privileged software monitor that in turn implements enclaves. The monitor's correctness is ensured by a machine-checkable proof of both functional correctness and high-level security properties of enclave integrity and confidentiality. We show that the approach is practical and performant with a concrete implementation of a prototype in verified assembly code on ARM TrustZone. Our ultimate goal is to achieve security equivalent to or better than SGX while enabling deployment of new enclave features independently of CPU upgrades. The Komodo specification, prototype implementation, and proofs are available at https://github.com/Microsoft/Komodo.
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Notary: a device for secure transaction approval
Notary is a new hardware and software architecture for running isolated approval agents in the form factor of a USB stick with a small display and buttons. Approval agents allow factoring out critical security decisions, such as getting the user's approval to sign a Bitcoin transaction or to delete a backup, to a secure environment. The key challenge addressed by Notary is to securely switch between agents on the same device. Prior systems either avoid the problem by building single-function devices like a USB U2F key, or they provide weak isolation that is susceptible to kernel bugs, side channels, or Rowhammer-like attacks. Notary achieves strong isolation using reset-based switching, along with the use of physically separate systems-on-a-chip for agent code and for the kernel, and a machine-checked proof of both the hardware's register-transfer-level design and software, showing that reset-based switching leaks no state. Notary also provides a trustworthy I/O path between the agent code and the user, which prevents an adversary from tampering with the user's screen or buttons. We built a hardware/software prototype of Notary, using a combination of ARM and RISC-V processors. The prototype demonstrates that it is feasible to verify Notary's reset-based switching, and that Notary can support diverse agents, including cryptocurrencies and a transaction approval agent for traditional client-server applications such as websites. Measurements of reset-based switching show that it is fast enough for interactive use. We analyze security bugs in existing cryptocurrency hardware wallets, which aim to provide a similar form factor and feature set as Notary, and show that Notary's design avoids many bugs that affect them.
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- PAR ID:
- 10206980
- Date Published:
- Journal Name:
- Proceedings of the 27th ACM Symposium on Operating Systems Principles (SOSP 2019)
- Page Range / eLocation ID:
- 97 to 113
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1145/3341301.3359661
