Decorative Cryptography

All encryption is end-to-end, if you’re not picky about the ends. config TCG_TPM2_HMAC bool "Use HMAC and encrypted transactions on the TPM bus" default n select CRYPTO_ECDH select CRYPTO_LIB_AESCFB select CRYPTO_LIB_SHA256 select CRYPTO_LIB_UTILS help Setting this causes us to deploy a scheme which uses request and response HMACs in addition to encryption for communicating with the TPM to prevent or detect bus snooping and interposer attacks (see tpm-security.rst). Saying Y here adds some encryption overhead to all kernel to TPM transactions. Last year, I came agross a Linux kernel feature called TCG_TPM2_HMAC. It claims to detect or prevent active and passive interposer attackers. That’s one of my sleeper agent activation phrases, so I dug in. TCG_TPM2_HMAC lives primarily in drivers/char/tpm/sessions.c and is discussed at further length in Documentation/security/tpm/tpm-security.rst. It all sounds really great. We should care about interposer adversaries. It’s great to use the TPM…