My laptop doesn't have TPM. If I enable BL PIN and someone steals my laptop and remove the drive, will they be able to read it's content on another computer? How am I vulnerable without TPM?


1 Answer 1


With just a PIN and no TPM (or removable key storage such as a USB drive or a smartcard that you need to insert to boot), it's impossible to have any meaningful security against an adversary who can access the encrypted drive. It's only a protection against someone casually walking to your desk, inserting a USB stick and rebooting your computer from the stick.

The adversary can just try all possible PIN, since all the information needed to decrypt the drive has to be present on the drive apart from the PIN. There are too few possible values for a PIN for it to be more than a moderate barrier to attack. For example, if unlocking takes 1 second of CPU time (which is an overapproximation), then a 6-digit PIN will resist for less than 12 days. A 4-digit PIN would fall in less than 1 hour and even an 8-digit PIN is manageable in 3 years of cumulated CPU time.

A strong password is a different deal because there are far more candidates for the attacker to try. A “correct horse battery staple”-type password (4 randomly generated words) would resist for around 300,000 years of cumulated CPU time.

A TPM changes the deal because when it's available, the encryption key is not derived from the PIN, but stored in the TPM. The TPM adds an additional protection: if there are too many failed attempts at guessing the PIN, it locks itself against further attempts. For the adversary to have a meaningful chance of decrypting your data, they would need to attack the TPM itself and extract the key from it, which is a lot harder than plugging the hard disk into a PC and making its CPU churn.

  • 1
    300,000 years is enough for me 👍🏻
    – Eduardo M
    May 26, 2020 at 1:39
  • This may have changed in last 18months, but have just setup bitlocker without TPM and was given option to use password, not just a pin.
    – Michael
    Dec 23, 2022 at 10:50
  • So TPM is another useless windows feature, no wonder why Linux encryption on the same machine does not raise additional troubles and just does its job. Got it. Thank you a lot for the excellent explanation.
    – fires3as0n
    Jan 12 at 4:07
  • Bitlocker without TPM does not use the PIN as a key. I believe it derives the key from the hardware configuration (things like MAC address). You can see this (on non-domain PCs) because when booting, it already logs you on, and the PIN just unlocks the screen. For instance check the start time of various tray icon processes- they start before inputing the PIN. May 21 at 19:59
  • @MariusBjørnstad The key is not derived from the hardware configuration. It's stored in the TPM. It's not related to the PIN: the PIN is an authorization for the TPM to unblock the use of the key. May 21 at 20:20

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