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Changing mbr or os kernel will change pcr values data

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Unformatted text preview: t four hardware counters –  Increment rate: every 5 seconds for 7 years. •  Applica2ons: –  Provide 2me stamps on blobs. –  Supports “music will pay for 30 days” policy. Dan Boneh Trusted Compu2ng Using PCRs aHer boot Dan Boneh Using PCRs after boot Applica2on: encrypted (a.k.a sealed) storage. Setup step 1: TPM_TakeOwnership( OwnerPassword, … ) •  Creates 2048- bit RSA Storage Root Key (SRK) on TPM •  Cannot run TPM_TakeOwnership again without OwnerPwd: –  Ownership Enabled Flag ← False •  Done once by IT department or laptop owner. (op4onal) Step 2: TPM_CreateWrapKey / TPM_LoadKey •  Create more RSA keys on TPM protected by SRK •  Each key iden2fied by 32- bit keyhandle Dan Boneh Implementing Protected Storage TPM_Seal: Encrypt data using RSA key on TPM. (some) Arguments: –  keyhandle: which TPM key to encrypt with –  KeyAuth: Password for using key `keyhandle’ –  PcrValues: PCRs to embed in encrypted blob (named by PCR num.) –  data block: at most 256 bytes [e.g. an AES key] Returns encrypted blob. Main point: blob can only be decrypted with TPM_Unseal when PCR- reg- vals = PCR- vals in blob. TPM_Unseal fails othrwise Dan Boneh Protected Storage Embedding PCR values in blob ensures that only specific apps can decrypt data. –  Changing MBR or OS kernel will change PCR values ⇒ da...
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