I wondered that too - apparently in Vista the PIN was only used to authenticate to the TPM and retrieve the volume master key (which in turn protects the key us

I wondered that too - apparently in Vista the PIN was only used to authenticate to the TPM and retrieve the volume master key (which in turn protects the key used to actually encrypt the drive). More pleasingly however, in Windows 7 and onwards it is used to encrypt the volume master key as well, in pretty much the way you describe. Microsoft's submissions for FIPS validation have some good detail on this - Windows 7 [see section 7]: http://csrc.nist.gov/groups/STM/cmvp/documents/140-1/140sp/140sp1332.pdf http://csrc.nist.gov/groups/STM/cmvp/documents/140-1/140sp/1..., others: https://www.google.com/search?q=site:csrc.nist.gov+inurl:140sp+microsoft+bitlocker https://www.google.com/search?q=site:csrc.nist.gov+inurl:140...