HW-based Mobile Platform Security

Question 1

Trusted Execution Environment

Answer 1

• Isolated and integrity-protected
  from the „normal“ execution environment (Rich Execution Environment)
• Processor, memory, storage, peripherals

Question 2

REE vs. TEE

Answer 2

• REE:
  -> Standard execution environment
  -> Untrusted
• TEE:
  -> Coexistent to REE
  -> Stronger security guarantees

Question 3

TEE Services

Answer 3

• Platform integrity („boot integrity“)
  -> Secure boot, authenticated boot
• Secure storage
• Isolated execution
  -> TEE
• Device identification
• Device authentication
  -> Remote attestation

Question 4

Architectures with single TEE

Answer 4

• ARM TrustZone
• TI M-Shield
• Smart card
• Crypto co-processor
• Trusted Platform Module (TPM)

Question 5

Architectures with multiple TEEs

Answer 5

• Intel SGX
• TON
• Hypervisor

Question 6

TEE Hardware Realization Alternatives

Answer 6

• External Secure Element (TPM, Smart Card)
• Embedded Secure Element
• Processor Secure Environment (TrustZone, M-Shield)

Question 7

Welche Komponenten gehören zur TCB - Platform Integrity?

Answer 7

• Verification Root
  -> Device manufacturer public key
• Cryptographic mechanisms
  -> Signature verification algorithm
• Volatile memory
  -> Stores measurements for authenticated boot
• Boot sequence
  -> Boot code certificate: certified by device manufacturer

Question 8

Welche Komponenten gehören zur TCB - Secure Storage?

Answer 8

• Cryptographic mechanisms
  -> Encryption algorithm
• Device Key
  -> Protected memory
• Non-volatile memory
  -> Rollback protection

Question 9

Welche Komponenten gehören zur TCB - Isolated Execution

Answer 9

• Verification Root
  -> TA code certificate (certified by device manufacturer), TA code hash
• Cryptographic Mechanisms
• Volatile Memory
• Trusted application
• TEE management layer
  -> controls TA execution

Question 10

Welche Komponenten gehören zur TCB - Device Authentication (and Remote Attestation)

Answer 10

• Cryptographic mechanisms
• Volatile memory
  -> Sign system state in remote attestation
• Device key
  -> Used to protect/derive signature key
• Non-volatile memory

Question 11

TrustZone Example Process

Answer 11

1) Boot begins in SW Supervisor mode (set access control)
2) Copy code and keys from on-chip ROM to on-chip RAM
3) Configure address controller (protect on-chip memory)
4) Prepare for Normal World Boot
5) Jump to Normal World Supervisor for traditional boot (set NS flag to 1)
6) Set up trusted application execution
7) Execute trusted application