On Tue, Mar 03, 2020 at 03:39:08PM -0500, James Bottomley wrote: > On Tue, 2020-03-03 at 21:33 +0200, Jarkko Sakkinen wrote: > > On Mon, Mar 02, 2020 at 07:27:56AM -0500, James Bottomley wrote: > > > In TPM 1.2 an authorization was a 20 byte number. The spec > > > actually recommended you to hash variable length passwords and use > > > the sha1 hash as the authorization. Because the spec doesn't > > > require this hashing, the current authorization for trusted keys is > > > a 40 digit hex number. For TPM 2.0 the spec allows the passing in > > > of variable length passwords and passphrases directly, so we should > > > allow that in trusted keys for ease of use. Update the 'blobauth' > > > parameter to take this into account, so we can now use plain text > > > passwords for the keys. > > > > > > so before > > > > > > keyctl add trusted kmk "new 32 > > > blobauth=f572d396fae9206628714fb2ce00f72e94f2258f" > > > > > > after we will accept both the old hex sha1 form as well as a new > > > directly supplied password: > > > > > > keyctl add trusted kmk "new 32 blobauth=hello keyhandle=81000001" > > > > > > Since a sha1 hex code must be exactly 40 bytes long and a direct > > > password must be 20 or less, we use the length as the discriminator > > > for which form is input. > > > > > > Note this is both and enhancement and a potential bug fix. The TPM > > > 2.0 spec requires us to strip leading zeros, meaning empyty > > > authorization is a zero length HMAC whereas we're currently passing > > > in > > > 20 bytes of zeros. A lot of TPMs simply accept this as OK, but the > > > Microsoft TPM emulator rejects it with TPM_RC_BAD_AUTH, so this > > > patch > > > makes the Microsoft TPM emulator work with trusted keys. > > > > The commit message does not mention it but there limitation that you > > cannot have this as a *password*: > > > > f572d396fae9206628714fb2ce00f72e94f2258f > > > > The commit message should explicitly state this. > > Well, that's impossible anyway: the password can be at most > TPM_DIGEST_SIZE characters and the above is twice that, so the > discriminator is fairly simple: if the string size is less than or > equal to TPM_DIGEST_SIZE, then it's a plain password, if it's exactly > 2xTPM_DIGEST_SIZE it must be a hex value and if it's anything else, > it's illegal. I thought the sentence > > Since a sha1 hex code must be exactly 40 bytes long and a direct > password must be 20 or less, we use the length as the discriminator > for which form is input. > > Was the explanation for this, but I can update it. Thanks! No need to update. I missed that part somehow. /Jarkko
