Linaro Connect San Diego 2019

Till now all keys stored in OP-TEE secure storage are secured at rest by encrypting it with FEK.
But when these keys are being used for operations these keys are kept in plain format in OP-TEE internal structures.

This is because cryptographic operations in OP-TEE are currently done with software libraries(libtomcypt and mbedTLS), and cryptographic operations are nothing but mathematical operations, so software libraries need private keys in “plain format” for operations.

Keeping these keys in plain format makes them vulnerable to following attacks with respect to confidentiality and integrity which is main objective of Trusted Execution Environment.
- By exploiting any vulnerability in code such as buffer overrun or bugs like Heartbleed.
- Using side channel attacks such as cold boot attack - in which an attacker with physical access to a computer performs a memory dump of a computer's RAM by performing a hard reset of the target machine.

Since nature of hardware-based cryptography ensures that the information stored in hardware is better protected from external attacks, so above issue can be fixed when these keys are backed by some hardware component. We need some mechanism in which the keys doesn’t exist in plain format in secure memory.

Hardware component will export the private keys only in encrypted form to secure memory.
During operations takes private keys in encrypted form and convert them into plain format internally and do operations with them.
Even If attacker gets access to this key in secure memory somehow, will not be able to find out the actual key.

Protecting key confidentiality is essential for many kernel security use-cases such as disk encryption, file encryption and protecting the integrity of file metadata. Trusted and encrypted keys provides a mechanism to export keys to user-space for storage as an encrypted blob and for the user-space to later reload them onto Linux keyring without the user-space knowing the encryption key. The existing Trusted Keys implementation relied on a TPM device but what if you are working on a system without one?

This session will introduce a Trusted Keys implementation which relies on a much simpler trusted application running in a Trusted Execution Environment (TEE) for sealing and unsealing of Trusted Keys using a hardware unique key provided by the TEE.