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> if you want to store secrets that don't need a user password to unlock and can't be stolen by taking apart the computer, you need a TPM I had a Win 7 system

> if you want to store secrets that don't need a user password to unlock and can't be stolen by taking apart the computer, you need a TPM I had a Win 7 system and just entered a password on boot, this decrypted the disk. It was supported without mods or TPM (maybe some registry tweaks though). On Ubuntu I do the same, no need for TPM. Am I missing something? My disk is encrypted. If they take it apart, they need my password to crack the encryption.

Cu3PO42 1y ago
The important part in the parent is "that don't need a user password". You just said you had to supply a (user) password. With a TPM you can set it up that your disk is unlocked automatically, but only if no-one changed anything in the signed boot chain. This is the default with Bitlocker on Windows and is also possible on Linux, though somewhat more finicky.
- beeflet 1y ago
  but why bother? I can fit enough entropy in my head to make my hard drive uncrackable, and I can back up my data even if some chip breaks. It's just added complexity and corporate control so people can use worse passwords
  - repiret 1y ago
    But most people don't want to enter a password, and if you make people enter a password too much, they'll choose terrible passwords and put them on a sticky note. Windows Hello can only be done securely with a TPM. A server that I want to turn back on all by itself after a power outage can only be done securely with a TPM. I want a TPM in my computer so I can have the security and convenience. Yes, it's another point of failure. But I need backups in case the hard drive fails anyway. And besides, the OS can be designed so I can enter a password if I need to use the drive without the TPM.
    - beeflet 1y ago
      >Windows Hello can only be done securely with a TPM I think in general biometrics are in the same ballpark as low-entropy passwords. IDK, I personally have no faith in trusted computing hardware because it can be broken with the right equipment. You're right that it can be used alongside ordinary security measures, but I just think it encourages putting your eggs into a cryptographicially-weak hardware-strong basket (which represents a downgrade because crypto is stronger than hw). >A server that I want to turn back on all by itself after a power outage can only be done securely with a TPM. Can you describe how this prevents a MITM attack? I assume you mean a remote server? I've heard of colocation setups like this, but I think they rely on a couple of unstated assumptions.
      - KAMSPioneer 1y ago
        > >A server that I want to turn back on all by itself after a power outage can only be done securely with a TPM. > Can you describe how this prevents a MITM attack? I assume you mean a remote server? I've heard of colocation setups like this, but I think they rely on a couple of unstated assumptions. I'm not sure what you mean by prevent a MitM attack, unless you're worried about someone with probes MitM-ing your TPM-CPU connection in the DC. You can bind a TPM to measurements on the host (let's say for argument's sake you want Secure Boot state, Option ROM state, and UEFI state), then configure the OS to ask the TPM for the (or rather, a) decryption key during boot. The TPM will check that the state(s) you bound to is (are) the same as when you bound them, and if so it will give the OS the key. Your disk is encrypted, but the boot process is automatic/unattended, as well as completely contained within the server chassis. There are ways to attack this hypothetical setup, buuuuut there are ways to attack remotely entering your disk password as well, and bear in mind that denial of service is a security vulnerability. Tradeoffs.
      - repiret 1y ago
        I agree that biometrics are in the same ballpark as low-entropy passwords, which means their security relies on avoiding offline attacks. My ATM card is protected by a 4-digit pin. That's perfectly secure, because the ATM network won't let you enter a wrong pin more than a single-digit number of times before locking the account. Windows Hello allows you to log in with a 6-digit pin. That's perfectly secure, because the TPM lets them design a system where you can't do an offline attack on the pin. Too many wrong entries and you'll need to use your password. I doubt there's more than two dozen bits of entropy provided by finger print readers or facial recognition authentication, but you can make an acceptably secure login experience with it because, again, the TPM lets you prevent offline attacks.
- edg5000 1y ago
  But without password, anybody can physically access the device and exfiltrate data. That is even easier than regular password protection, where the storage medium would have to be removed or a live OS would have to be booted. The risk is data leakage. With a TPM and no password, there is no data leakage protection.
  - repiret 1y ago
    Passwordless boot with a TPM means the software can control what secrets it gives out. Yeah, if you boot to a desktop operating system and auto-login as an admin user, that doesn't leave things very secure, but that's not the only scenario. Consider a server. It can have an encrypted hard drive, boot with the TPM without a password, and run its services. In order to steal data from it, you need to either convince software running on the server to give you that data, or you need to do some sort of advanced hardware attack, like trying to read the contents of DRAM while the computer is running. There are other use cases too, like kiosks, booting to a guest login, corporate owned laptops issued to employees, allowing low-entropy (but rate limited) authentication after booting, to name a few.
bpye 1y ago
> Am I missing something? My disk is encrypted. If they take it apart, they need my password to crack the encryption. You’re not protected from an evil maid attack. An attacker with physical access could make your device boot their own payload to capture your encryption key and install a rootkit.
- AnthonyMouse 1y ago
  So what happens when they use their physical access to turn off secure boot or just replace the component/device with one that looks the same, prompts for your password and sends it to them?
  - Ferret7446 1y ago
    There is no password. The machine will fail to boot and decrypt you hard drive.
    - AnthonyMouse 1y ago
      Either you're entering something into the machine to authenticate yourself or they can just copy or modify your files without authenticating to begin with. If they just want your password they don't need to decrypt your hard drive, they can format it and install a rootkit that steals your password as soon as you try to login.
    - jasomill 1y ago
      So don't turn off secure boot. Replace the target machine with an identical decoy machine set up to capture whatever credentials are required to log in to the machine once BitLocker auto-unlocks, then use these to log in to Windows on the original machine and steal any encrypted data accessible by the user who logs in. This would be more difficult to pull off in the presence of non-password security like a hardware token, as you'd need to forward the actual login UI to the decoy machine, but still not terribly difficult if the login UI will display on an externally-connected monitor and accept input from an externally-connected keyboard and pointing device, and the hardware security device connects via an external interface like USB.

Cu3PO42 1y ago

The important part in the parent is "that don't need a user password". You just said you had to supply a (user) password. With a TPM you can set it up that your disk is unlocked automatically, but only if no-one changed anything in the signed boot chain. This is the default with Bitlocker on Windows and is also possible on Linux, though somewhat more finicky.

beeflet 1y ago
but why bother? I can fit enough entropy in my head to make my hard drive uncrackable, and I can back up my data even if some chip breaks. It's just added complexity and corporate control so people can use worse passwords
- repiret 1y ago
  But most people don't want to enter a password, and if you make people enter a password too much, they'll choose terrible passwords and put them on a sticky note. Windows Hello can only be done securely with a TPM. A server that I want to turn back on all by itself after a power outage can only be done securely with a TPM. I want a TPM in my computer so I can have the security and convenience. Yes, it's another point of failure. But I need backups in case the hard drive fails anyway. And besides, the OS can be designed so I can enter a password if I need to use the drive without the TPM.
  - beeflet 1y ago
    >Windows Hello can only be done securely with a TPM I think in general biometrics are in the same ballpark as low-entropy passwords. IDK, I personally have no faith in trusted computing hardware because it can be broken with the right equipment. You're right that it can be used alongside ordinary security measures, but I just think it encourages putting your eggs into a cryptographicially-weak hardware-strong basket (which represents a downgrade because crypto is stronger than hw). >A server that I want to turn back on all by itself after a power outage can only be done securely with a TPM. Can you describe how this prevents a MITM attack? I assume you mean a remote server? I've heard of colocation setups like this, but I think they rely on a couple of unstated assumptions.
    - KAMSPioneer 1y ago
      > >A server that I want to turn back on all by itself after a power outage can only be done securely with a TPM. > Can you describe how this prevents a MITM attack? I assume you mean a remote server? I've heard of colocation setups like this, but I think they rely on a couple of unstated assumptions. I'm not sure what you mean by prevent a MitM attack, unless you're worried about someone with probes MitM-ing your TPM-CPU connection in the DC. You can bind a TPM to measurements on the host (let's say for argument's sake you want Secure Boot state, Option ROM state, and UEFI state), then configure the OS to ask the TPM for the (or rather, a) decryption key during boot. The TPM will check that the state(s) you bound to is (are) the same as when you bound them, and if so it will give the OS the key. Your disk is encrypted, but the boot process is automatic/unattended, as well as completely contained within the server chassis. There are ways to attack this hypothetical setup, buuuuut there are ways to attack remotely entering your disk password as well, and bear in mind that denial of service is a security vulnerability. Tradeoffs.
    - repiret 1y ago
      I agree that biometrics are in the same ballpark as low-entropy passwords, which means their security relies on avoiding offline attacks. My ATM card is protected by a 4-digit pin. That's perfectly secure, because the ATM network won't let you enter a wrong pin more than a single-digit number of times before locking the account. Windows Hello allows you to log in with a 6-digit pin. That's perfectly secure, because the TPM lets them design a system where you can't do an offline attack on the pin. Too many wrong entries and you'll need to use your password. I doubt there's more than two dozen bits of entropy provided by finger print readers or facial recognition authentication, but you can make an acceptably secure login experience with it because, again, the TPM lets you prevent offline attacks.
edg5000 1y ago
But without password, anybody can physically access the device and exfiltrate data. That is even easier than regular password protection, where the storage medium would have to be removed or a live OS would have to be booted. The risk is data leakage. With a TPM and no password, there is no data leakage protection.
- repiret 1y ago
  Passwordless boot with a TPM means the software can control what secrets it gives out. Yeah, if you boot to a desktop operating system and auto-login as an admin user, that doesn't leave things very secure, but that's not the only scenario. Consider a server. It can have an encrypted hard drive, boot with the TPM without a password, and run its services. In order to steal data from it, you need to either convince software running on the server to give you that data, or you need to do some sort of advanced hardware attack, like trying to read the contents of DRAM while the computer is running. There are other use cases too, like kiosks, booting to a guest login, corporate owned laptops issued to employees, allowing low-entropy (but rate limited) authentication after booting, to name a few.

bpye 1y ago

> Am I missing something? My disk is encrypted. If they take it apart, they need my password to crack the encryption. You’re not protected from an evil maid attack. An attacker with physical access could make your device boot their own payload to capture your encryption key and install a rootkit.

AnthonyMouse 1y ago
So what happens when they use their physical access to turn off secure boot or just replace the component/device with one that looks the same, prompts for your password and sends it to them?
- Ferret7446 1y ago
  There is no password. The machine will fail to boot and decrypt you hard drive.
  - AnthonyMouse 1y ago
    Either you're entering something into the machine to authenticate yourself or they can just copy or modify your files without authenticating to begin with. If they just want your password they don't need to decrypt your hard drive, they can format it and install a rootkit that steals your password as soon as you try to login.
  - jasomill 1y ago
    So don't turn off secure boot. Replace the target machine with an identical decoy machine set up to capture whatever credentials are required to log in to the machine once BitLocker auto-unlocks, then use these to log in to Windows on the original machine and steal any encrypted data accessible by the user who logs in. This would be more difficult to pull off in the presence of non-password security like a hardware token, as you'd need to forward the actual login UI to the decoy machine, but still not terribly difficult if the login UI will display on an externally-connected monitor and accept input from an externally-connected keyboard and pointing device, and the hardware security device connects via an external interface like USB.