NeonMan
10th February 2008, 03:05
Hi!
I've go a laptop with a TPM (Fritz chip?) on it, running both windows XP and Linux. My question is rather simple but I couldn't find the answer:
Knowing that:
The TMP is tamper-proof but with limited storage
Is NOT a cryptographic accelerator (meaning it's SLOW and cheap)
Cannot load custom code (as far as I know)
With this things on mind, How does the TMP prevent us from retrieving (ie AACS decryption keys) plaintext data from memory?
Those key MUST be loded on a process able to sustain HIGH data rates (the TPM cannot do that) so, they must be used, and temporally stored on the main memory.
The keys MUST be loaded somehow into the tpm, again if ecc-encrypted they must be encrypted somehow in either main memory or sending them as plaintext to the TPM.
Aswell someone may force the upload of keys to the TPM by simply erasing it from Bios setup having another oportunity to capture the key.
And as a final comment, the TPM could be emulated in software modifying virtualizing programs like XEN or Qemu
As a test, I've used the tpm to store the keys needed to decrypt a Loop-AES encrypted disk, The tpm stores the key of the IV's File so, the key is retrieved (and loaded in main memory), the IV's file is decrypted and the disk is then mounted.
I've go a laptop with a TPM (Fritz chip?) on it, running both windows XP and Linux. My question is rather simple but I couldn't find the answer:
Knowing that:
The TMP is tamper-proof but with limited storage
Is NOT a cryptographic accelerator (meaning it's SLOW and cheap)
Cannot load custom code (as far as I know)
With this things on mind, How does the TMP prevent us from retrieving (ie AACS decryption keys) plaintext data from memory?
Those key MUST be loded on a process able to sustain HIGH data rates (the TPM cannot do that) so, they must be used, and temporally stored on the main memory.
The keys MUST be loaded somehow into the tpm, again if ecc-encrypted they must be encrypted somehow in either main memory or sending them as plaintext to the TPM.
Aswell someone may force the upload of keys to the TPM by simply erasing it from Bios setup having another oportunity to capture the key.
And as a final comment, the TPM could be emulated in software modifying virtualizing programs like XEN or Qemu
As a test, I've used the tpm to store the keys needed to decrypt a Loop-AES encrypted disk, The tpm stores the key of the IV's File so, the key is retrieved (and loaded in main memory), the IV's file is decrypted and the disk is then mounted.