Device Unlock Credential Sharing

The credentials necessary for unlocking a device are shared across multiple parties and may expose sensitive information.


Description

“Unlocking a device” often means activating certain, unadvertised, debug and manufacturer-specific capabilities of a device using sensitive credentials. Unlocking a device might be necessary for the purpose of troubleshooting device problems. For example, suppose a device contains the ability to dump the content of the full system memory by disabling the memory-protection mechanisms. Since this is a highly security-sensitive capability, this capability is “locked” in the production part. Unless the device gets unlocked by supplying the proper credentials the debug capablilities are not available. For cases where the chip designer, chip manufacturer (fabricator), and manufacturing and assembly testers are the all employed by the same company, the compromise of the credentials are greatly reduced. However, when the chip designer is employed by one company, the chip manufacturer is employed by another company (a foundry), and the assemblers and testers are employed by yet a third company. Since these different companies will need to perform various tests on the device to verify correct device function, they all need to share the unlock key. Unfortunately, the level of secrecy and policy might be quite different at each company, greatly increasing the risk of sensitive credentials being compromised.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

This example shows how an attacker can take advantage of compromised credentials.

Suppose a semiconductor chipmaker, “C”, uses the foundry “F” for fabricating its chips. Now, F has many other customers in addition to C, and some of the other customers are much smaller companies. F has dedicated teams for each of its customers, but somehow it mixes up the unlock credentials and sends the unlock credentials of C to the wrong team. This other team does not take adequate precautions to protect the credentials that have nothing to do with them, and eventually the unlock credentials of C get leaked.

When the credentials of multiple organizations are stored together, exposure to third parties occurs frequently.

Vertical integration of a production company is one effective method of protecting sensitive credentials. Where vertical integration is not possible, strict access control and need-to-know are methods which can be implenmented to reduce these risks.

See Also

Manufacturing and Life Cycle Management Concerns

Weaknesses in this category are root-caused to defects that arise in the semiconductor-manufacturing process or during the life cycle and supply chain.

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