On Thu, Mar 05, 2026 at 10:37:08AM -0500, Mimi Zohar wrote: > On Tue, 2026-03-03 at 23:32 +0200, Jarkko Sakkinen wrote: > > On Fri, Feb 20, 2026 at 10:30:26AM -0800, Chris Fenner wrote: > > > My conclusion about TCG_TPM2_HMAC after [1] and [2] was that > > > TPM2_TCG_HMAC doesn't (or didn't at the time) actually solve the > > > threat model it claims to (active interposer adversaries), while > > > dramatically increasing the cost of many kernel TPM activities beyond > > > the amount that would have been required to just solve for > > > passive/bus-sniffer interposer adversaries. The added symmetric crypto > > > required to secure a TPM transaction is almost not noticeable; the big > > > performance problem is the re-bootstrapping of the session with ECDH > > > for every command. > > > > > > My primary concern at that time was, essentially, that TCG_TPM2_HMAC > > > punts on checking that the key that was used to secure the session was > > > actually resident in a real TPM and not just an interposer adversary. > > > I wrote up my understanding at > > > https://www.dlp.rip/decorative-cryptography, for anyone who wants a > > > long-form opinionated take :). > > > > > > Unless I'm wrong, or TCG_TPM2_HMAC has changed dramatically since > > > August, I don't think "TPM2_TCG_HMAC makes this too costly" is a > > > compelling reason to make a security decision. (There could be other > > > reasons to make choices about whether to use the TPM as a source of > > > randomness in the kernel! This just isn't one IMHO.) > > > > > > The version of TCG_TPM2_HMAC that I'd like to see someday would be one > > > that fully admits that its threat model is only passive interposers, > > > and sets up one session upon startup and ContextSaves/ContextLoads it > > > back into the TPM as needed in order to secure parameter encryption > > > for e.g., GetRandom() and Unseal() calls. > > > > Neither agreeing nor disagreeing but this patch set clearly does not > > move forward and I spent already enough energy for this. For better > > ideas the patches are available in queue branch. > > Jarkko, you totally ignored my comments below. I object to your removing the > TPM trusted-keys RNG support.
It has not been removed but I can keep the patches still backed up in a branch, can't I? BR, Jarkko
