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Confidential Computing Consortium Scope

Executive Summary

  • The scope of the Confidential Computing Consortium (CCC) is to "promote the widespread use of hardware-based trusted execution environments".

  • The CCC uses, and recommends the rest of the industry also use, the definition: "Confidential Computing is the protection of data in use by performing computation in a hardware-based Trusted Execution Environment."

  • For both the scope of the CCC, and the definition of confidential computing, the following terms are to be avoided in ways that imply constraints, as being technically problematic: "cloud", "main processor", and "encrypted"/"encryption".

  • Similarly, any language implying that "protecting data in use" is synonymous with "confidential computing" is also to be avoided, as the latter is only a subset of technologies for the former.

1. Related Terminology

The CCC's Technical Advisory Council (TAC) conducted a survey of various terms in the industry related to protecting data in use, and composed the following Venn diagram of technologies:

Figure 1: Related Terminology

Definitions of the various terms in the diagrams can be found in Appendix A.

The solid blue lines indicate that the area is clearly in scope for CCC discussion and projects. The dotted blue lines indicate that other areas would not normally fall under the CCC's definition of Confidential Computing, and would be in scope of the CCC only if a project in the area could be argued to "promote the widespread use of" Confidential Computing. For example, a library that performed encryption/decryption inside a hardware-based TEE, for use with Homomorphic Encryption, would be relevant to the CCC.

Unfortunately, several of the terms used in the diagram have multiple competing definitions. For example, "privacy-preserving computation" is variously defined as being (a) synonymous with multi-party computation, or (b) covering both multi-party computation and homomorphic encryption, or even (c) covering the entire space of protecting data in use.

There are other relevant standards bodies operating in the overall space, as depicted in the following diagram:

Figure 2: Related Organizations

These organizations include:

In addition to those shown in the diagram:

  • ISO/IEC JTC1/SC27 is now doing work (N 20273) on multiparty computation and may expand to other areas, and the ITU has published the UN Handbook on Privacy-Preserving Computation Techniques that covers the entire space of the diagram, even though it has "privacy-preserving computation" in the title. While the ISO work is based on member states, the ITU work has a multistakeholder model.
  • TrustedFirmware.org is another consortium with related open-source projects, including projects for Arm trusted firmware, OP-TEE (a lightweight TEE OS), and mbedTLS.
  • FIDO Alliance develops strong user authentication standards leveraging some Trusted Execution Environments (TPMs, embedded Secure Elements, etc.).

Based on the CCC scoping, various relationships (e.g., liaisons) might be appropriate in the future. (Most of the organizations listed are not legal entities hosting open source projects, but do publish relevant specifications.)

2. Fine-Grained Axes

In discussing Trusted Execution Environments, the TAC started by creating a rough taxonomy of five roughly orthogonal axes, each with a spectrum of narrow-to-broad options:

  1. Hardware/software only or also algorithmic (mathematical)? The CCC focus is on promoting the hardware/software end, which excludes purely algorithmic technologies such as homomorphic encryption and multiparty computation.

  2. Hardware-based (+firmware?) required or also software-only? The CCC position is that only hardware-rooted technologies can provide the desired level of security, in particular for attestation. Software only projects can be considered by the CCC if they demonstrably "promote" the use of hardware-backed solutions. (For example, a development-time-only emulation technology meant to speed development of hardware-backed solutions.)

  3. Generalized (fully programmable) only, or also configurable (semi-programmable) and even specialized (fixed-purpose, non-programmable) also? The CCC focus is on programmability, but it has not explicitly ruled out future submissions on other solutions.

  4. On-main CPU only, or also separate processors also? The CCC encompasses the entire spectrum here.

  5. Cloud only, or also on-premises (including IoT) also? The CCC encompasses the entire spectrum here.

The TAC also discussed that other attributes (e.g., TCB size) are also important security evaluation criteria for any given solution or project, but by themselves weren't considered to be part of the scoping definition per se.

The following table shows how various example technologies fall into the above axes, to help illustrate how answers would affect what sorts of projects might be accepted or rejected as a result:

Figure 3: Example Technologies

3. Confidential Computing Definitions

Prior to the CCC definition, there were various competing definitions of "confidential computing" including (possibly among others):

  • Gartner report 2019 definition: Confidential computing is the combination of CPU-based hardware technology and infrastructure as a service (IaaS) cloud provider virtual machine (VM) images and software tools that enable cloud-using organizations to create completely isolated trusted execution environments (TEE), also called enclaves. Because they offer a form of encryption of data in use, these enclaves render sensitive information invisible to host OSs and cloud providers.

The TAC observed the following issues with the above definition:

  1. It is constrained to only cloud, whereas the TAC consensus is that a broader scope is needed, even for projects already in the CCC.

  2. The term "encryption" is problematic since some TEEs of interest may have other forms of protecting data in use, encryption is just one example mechanism. That is, encryption is a specific mechanism rather than a property we are seeking. You can provide confidentiality by access control (for example) and not actually require encryption.

  • CCC press release: Established in 2019, the Confidential Computing Consortium brings together hardware vendors, cloud providers, developers, open source experts and academics to accelerate the confidential computing market; influence technical and regulatory standards; build open source tools that provide the right environment for TEE development' and host industry outreach and education initiatives. Its aims to address computational trust and security for data in use, enabling encrypted data to be processed in memory without exposing it to the rest of the system, reducing exposure to sensitive data and providing greater control and transparency for users.

The TAC observed the following issues with the above text:

  1. The use of "encrypted" is again seen as problematic.

  2. The text is ambiguous about the scope, as the text about tools is constrained to "TEE" development, but the aims are broader, applying to protecting "data in use", where all of Figure 1 would claim to be about protecting data in use.

  • Mark Russinovich blog: Put simply, confidential computing offers a protection that to date has been missing from public clouds, encryption of data while in use. ... Confidential computing ensures that when data is "in the clear," which is required for efficient processing, the data is protected inside a Trusted Execution Environment (TEE - also known as an enclave), an example of which is shown in the figure below. TEEs ensure there is no way to view data or the operations inside from the outside, even with a debugger. They even ensure that only authorized code is permitted to access data. If the code is altered or tampered, the operations are denied and the environment disabled. The TEE enforces these protections throughout the execution of code within it.

The use of "encrypted" was again seen as problematic. Also the definition is similarly ambiguous in that "data while in use" is broad (all of Figure 1) but then the discussion only mentions TEEs. (A request to Mark for clarification resulted in him answering that he did not intend the definition to be limited to TEEs.)

  • TechTarget definition: Confidential computing is a concept in which encrypted data can be processed in memory to limit access to ensure data in use is protected. Confidential computing is a concept promoted by the Confidential Computing Consortium, which is a group of organizations that wants to build tools supporting the protection of data. This concept is especially suitable for public clouds.

The use of "encrypted" was again seen as problematic. However, the rest of the definition is clearly broadly scoped to protecting data in use (not phrased to be limited to TEEs), and the article goes on to discuss the CCC after the above definition.

The TAC iterated on several proposals for wording around the scope of what projects the TAC would recommend as being in scope of the CCC. The following wording obtained rough consensus:

  • "promote the widespread use of hardware-based trusted execution environments".

This proposal puts the focus on hardware-based TEEs, while providing some leeway with the use of "promote" to allow for non-hardware based projects that demonstrably promote the use of hardware-based TEEs.

Similarly, the TAC iterated on several proposals for wording around the definition of the term "confidential computing". The following wording obtained consensus and was subsequently adopted by the CCC Governing Board:

  • CCC Definition: "Confidential Computing is the protection of data in use by performing computation in a hardware-based Trusted Execution Environment."

Subsequent to the adoption of the above definition by the Confidential Computing Consortium, Gartner's [Hype Cycle for Compute Infrastructure, 2020] (https://www.gartner.com/en/documents/3987268/hype-cycle-for-compute-infrastructure-2020) now includes the revised definition, which is consistent with the CCC's:

  • Gartner 2020 Definition: "Confidential computing is a security mechanism that executes code in a hardware-based trusted execution environment (TEE), also called an enclave. Enclaves isolate and protect code and data from the host system (plus the host system’s owners) and may also provide code integrity and attestation."

Appendix A. Related Terminology

A.1. Trusted Execution Environment (TEE)

There are many competing definitions of what a "TEE" is, many of which are listed below:

  • Wikipedia: A secure area of a main processor. It guarantees code and data loaded inside to be protected with respect to confidentiality and integrity. A TEE as an isolated execution environment provides security features such as isolated execution, integrity of applications executing with the TEE, along with confidentiality of their assets.

As noted earlier, the TAC dislikes the above definition because of its constraint to a "main" processor.

  • ARM website: a secure area inside a main processor. It runs in parallel of the operating system, in an isolated environment. It guarantees that the code and data loaded in the TEE are protected with respect to confidentiality and integrity.

Besides the "main" processor issue, another problem the TAC saw with the above definition is that it assumes there exists a regular operating system on the same processor. In some environments (MCUs, FPGAs, etc.), that is not necessarily the case.

  • GlobalPlatform: A device that conforms to specifications from GP's TEE Committee.

The above definition excludes various TEEs (including Intel SGX) from its definition, which the TAC finds problematic.

  • Mike Bursell's strawman: A hardware-based technique for securing sensitive data and algorithms in such a way that even the kernel, root user or hypervisor can't see what's going on

The above definition is narrowly scoped to only hardware-based TEEs, and thus excludes the items in Section A.1.1.

One relatively minor issue as worded is that it implies that the TEE has a kernel, root user, or hypervisor, which may or may not be the case.

  • IETF TEEP WG: An environment that enforces that any code within that environment cannot be tampered with, and that any data used by such code cannot be read or tampered with by any code outside that environment.

Thie above definition is broader, includes language similar to the broader text in the Mark Russinovich blog, and has no immediate flaws that the TAC found. Some individuals might like to see additional constraints added to it, but there is no consensus on such gaps and so the above definition is accepted by both the IETF and the CCC TAC. (Full disclosure: the TAC chair is also a co-editor of the IETF document with the above definition.)

A.1.1. Software TEE

There are multiple products and solutions today that are software-based and use the term "TEE", ranging from ones meant for production use, to ones meant just for development of code to be later used on hardware TEEs.

As one example:

  • QEMU: very widely used open source machine emulator. ... Developers can use the QEMU security extensions that emulate a given TEE to develop and work with Trusted Execution Environments (TEEs) that are likely to be the primary consumers of the added functionality.

A.2. Privacy-Preserving Computation

  • multi-party computation (MPC), or privacy-preserving computation: a subfield of cryptography with the goal of creating methods for parties to jointly compute a function over their inputs while keeping those inputs private. Unlike traditional cryptographic tasks, where cryptography assures security and integrity of communication or storage and the adversary is outside the system of participants (an eavesdropper on the sender and receiver), the cryptography in this model protects participants' privacy from each other.

  • Homomorphic encryption: a form of encryption that allows computation on ciphertexts, generating an encrypted result which, when decrypted, matches the result of the operations as if they had been performed on the plaintext. Homomorphic encryption can be used for privacy-preserving outsourced storage and computation. This allows data to be encrypted and out-sourced to commercial cloud environments for processing, all while encrypted.

Other sources discussing the relationship among these terms, that were instrumental in constructing Figure 1, include:

A.3. Other Terms

  • secure cryptoprocessor: a dedicated computer-on-a-chip or microprocessor for carrying out cryptographic operations, embedded in a packaging with multiple physical security measures, which give it a degree of tamper resistance. Unlike cryptographic processors that output decrypted data onto a bus in a secure environment, a secure cryptoprocessor does not output decrypted data or decrypted program instructions in an environment where security cannot always be maintained. The purpose of a secure cryptoprocessor is to act as the keystone of a security subsystem, eliminating the need to protect the rest of the subsystem with physical security measures.

  • Trusted Platform Module (TPM, also known as ISO/IEC 11889): an international standard for a secure cryptoprocessor, a dedicated microcontroller designed to secure hardware through integrated cryptographic keys.

  • hardware security module (HSM): a physical computing device that safeguards and manages digital keys for strong authentication and provides cryptoprocessing.

  • Secure Element (SE): a microprocessor chip which can store sensitive data and run secure apps such as payment. It acts as a vault, protecting what's inside the SE (applications and data) from malware attacks that are typical in the host (i.e. the device operating system).

  • Dedicated Security Component: the combination of a hardware component and its controlling firmware dedicated to providing the encompassing platform with services for the provisioning, protection, and use of Security Data Objects (SDOs) consisting of keys, identities, attributes, and other types of Security Data Elements (SDEs).