Changes between Version 4 and Version 5 of tpm

Timestamp:

02/07/2024 12:18:45 AM (3 months ago)

Author:

Ryan Erbstoesser

Comment:

add PCR values

tpm

@@ -1 +1 @@
 = Trusted Protection Module
-
+[[PageOutline]]
 Gateworks has an optional TPM on some SBCs.
 
@@ -61 +61 @@
 }}}
 
+== PCR Values
+
+Platform Configuration Registers (PCRs) are registers that represent ‘fingerprints’ of different pieces of a specific system. These pieces can be things such as the bootloader, Linux kernel, and Initramfs. If the stored PCR values in the TPM do not match the currently booting system PCRs, access will not be granted. For example, someone trying to boot a Ubuntu Live CD would not be able to access the TPM key as the PCRs generated from the original disk and stored in the TPM will not match the newly generated PCRs from the boot CD. PCRs use hashing and thus any new value is concatenated with the old and then hashed. This new hash will replace the old hash. The definition of each specific PCR register can be found online.   
+
+Read the PCR Values:
+{{{
+#!bash
+root@jammy-venice:~# tpm2_pcrread
+  sha1:
+    0 : 0x0000000000000000000000000000000000000000
+    1 : 0x0000000000000000000000000000000000000000
+    2 : 0x0000000000000000000000000000000000000000
+    3 : 0x0000000000000000000000000000000000000000
+    4 : 0x0000000000000000000000000000000000000000
+    5 : 0x0000000000000000000000000000000000000000
+    6 : 0x0000000000000000000000000000000000000000
+    7 : 0x0000000000000000000000000000000000000000
+    8 : 0x0000000000000000000000000000000000000000
+    9 : 0x0000000000000000000000000000000000000000
+    10: 0x0000000000000000000000000000000000000000
+    11: 0x0000000000000000000000000000000000000000
+    12: 0x0000000000000000000000000000000000000000
+    13: 0x0000000000000000000000000000000000000000
+    14: 0x0000000000000000000000000000000000000000
+    15: 0x0000000000000000000000000000000000000000
+    16: 0x0000000000000000000000000000000000000000
+    17: 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
+    18: 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
+    19: 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
+    20: 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
+    21: 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
+    22: 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
+    23: 0x0000000000000000000000000000000000000000
+  sha256:
+
+}}}
+
+== Clearing the TPM
+
+Only do this if you need to clear the TPM
+{{{
+tpm2_clear
+}}}
+