Show HN: ssh-tpm-agent – SSH agent for TPMs
What’s the threat model of TPM? They claim it’s for “physical attacks” but they can only enforce it when there is no software vulnerability or unauthorized privileged access anywhere so it’s a very small area of the Venn diagram where you have an attacker whose capability is “physical access” but also “does not possess any exploit or one-touch-access”. This narrows down the list to:<p>• Malicious coworkers, family members, and house keepers against a computer who is NEVER left unattended (i.e. screen locked when you leave 100% of the time)<p>• Local government agents (i.e. the local police) who can confiscate your powered on device but cannot afford to buy 3rd party cracking services that utilize exploits or more advanced extraction techniques (external RAM dumping)<p>• A device that is completely powered off and confiscated by a powerful nation state agent but not later on returned to the original owner and they forgot to wipe the device in case of implants.<p>In any case the design of TPM is completely flawed and suffers from “astronaut architects”. If you grep the three volume 1000+ pages of the TPM 2.0 architecture documents, you’ll not find a single mention of “threat model”.<p>Specifically TPM is a multi-million dollar industry signed on by many tech companies (including Microsoft who uses it as an excuse to get you to buy a new PC because TPM == more secure right, but also because older computers don’t support it) because places like governments and banks require it because they also don’t understand threat models.<p>TPM protection is fundamentally flawed because:<p>• It cannot protect against a compromise in the boot chain (e.g. a UEFI driver is exploited, and it lies to TPM about the subsequent stage of code that is loaded while running a malware implant)<p>• It cannot protect against RCE (remote code execution). This means if Windows ever has a vulnerability that can be exploited remotely, they can keylog -&gt; steal your PIN -&gt; replay it later to dump the key. Or just dump the key in memory if they have a PE (privilege escalation) as well.<p>• It cannot protect against a user volunteerly installing malware (Bonzi buddy?)<p>• It cannot protect against an attacker who installs something on your unattended computer (USB Rubber Ducky, Flipper Zero, etc)<p>Basically the most common ways people get compromised sees no protection from TPM while esoteric attack situations that no attacker will realistic attempt are protected.<p>TPM can never protect against these cases because it is logically (fTPM) and&#x2F;or physically (dTPM) separate from the CPU. That means it cannot perform any policy enforcement against a CPU whose execution is under control of the attacker.