# TPM Fingerprint Library - Architecture

## System Architecture

```

                     Application Layer                            
                                                                   
       
    CLI Tool       Examples        Your Application       
       

                                                 
          
                            

                    Library Core Layer                             
                                                                  
                                       
                 OfflineVerifier                                
                 (Orchestrator)                                 
                                       
                                                                  
                        
                                                              
                      
  Fingerprint         Policy        Consequence           
    Engine      Engine      Handler             
                      
                                                              
                        
                                                                 
                                                  
                      Audit Logger                             
                                                  
                                                                 
                     
                  TPM Operations Layer                        
                                                               
                           
         PCR Read    Challenge   Seal/                 
                     Response    Unseal                
                           
                     

                             

                Hardware Layer                                   
                                                                 
                                      
                   TPM 2.0 Hardware                            
                 (Trusted Platform                             
                  Module)                                      
                                                               
                  PCR Registers                               
                  Signing Keys                                
                  Sealing Keys                                
                  Random Number Gen                           
                                      

```

## Data Flow

### Enrollment Flow
```
1. Application Request
         
         
2. OfflineVerifier.enroll_device()
         
          FingerprintEngine.generate_fingerprint()
                    
                     TPMOps.read_pcrs()
                             TPM Hardware
                    
                     TPMOps.get_tpm_quote()
                             TPM Hardware (Sign)
                    
                     TPMOps.seal_data()
                              TPM Hardware (Seal)
         
          PolicyEngine.create_policy()
                     Store baseline PCRs
         
          Return: fingerprint_id, policy_id
```

### Verification Flow
```
1. Application Request
         
         
2. OfflineVerifier.verify_device()
         
          FingerprintEngine.load_fingerprint()
                    
                     TPMOps.unseal_data()
                              TPM Hardware (Unseal)
                                  
                                   FAIL if PCRs changed 
         
          FingerprintEngine.verify_fingerprint()
                    
                     TPMOps.generate_challenge()
                    
                     TPMOps.sign_challenge()
                             TPM Hardware (Sign)
                    
                     TPMOps.verify_challenge_response()
         
          PolicyEngine.validate_fingerprint()
                    
                     TPMOps.read_pcrs()
                             TPM Hardware
                    
                     Compare with baseline
                    
                     IF violation detected
                             
                              Trigger consequences
         
          AuditLogger.log_event()
                   TPMOps.seal_data() (for audit logs)
```

### Consequence Enforcement Flow
```
Policy Violation Detected
         
         
PolicyEngine triggers violation handlers
         
          ConsequenceHandler.enforce_consequences()
                    
                     revoke_credentials_for_fingerprint()
                               
                                Credential.revoke()
                                         Save state
                    
                     lock_vaults_for_fingerprint()
                               
                                Vault.lock()
                                         Save state
                    
                     invalidate_tokens_for_fingerprint()
                               
                                Token.invalidate()
                                         Save state
                    
                     record_consequence()
                              Save to history
         
          AuditLogger.log_policy_violation()
                   Sealed to TPM
```

## Component Interactions

### Component Dependency Graph
```

OfflineVerifier  (Facade - coordinates everything)

         
    
                             
                             
                             
  
FP  Pol Cons Audit TPM  
Eng Eng Hdlr Log   Ops  
  
                          
  
                
                
         
         TPM Hardware 
         

FP Eng   = FingerprintEngine
Pol Eng  = PolicyEngine
Cons Hdlr = ConsequenceHandler
Audit Log = AuditLogger
TPM Ops  = TPMOperations
```

## Storage Layout

```
~/.tpm_fingerprint/
 fingerprints/              # Sealed fingerprints
    abc123...sealed
    def456...sealed
    ghi789...sealed

 policies/                  # Policy definitions
    policy_001.json
    policy_002.json
    policy_003.json

 consequences/              # Consequence state
    credentials.json       # Registered credentials
    tokens.json           # Registered tokens
    vaults.json           # Registered vaults
    consequence_history.json

 sealed_logs/              # TPM-sealed audit logs
    log_20240101_120000.sealed
    log_20240101_130000.sealed
    log_20240101_140000.sealed

 current_log.json          # Current unsealed log
 audit.log                 # Text audit log
```

## Security Boundaries

```

              Untrusted Environment                   
      
           Application Code                        
      
                                                     
   Security Boundary 
                                                     
      
        TPM Fingerprint Library                   
    (Software - Protected by TPM binding)         
      
                                                     
   Hardware Boundary 
                                                     
      
              TPM 2.0 Hardware                    
     Protected Keys                              
     Sealed Storage                              
     PCR Registers                               
     Hardware RNG                                
     Tamper-resistant                            
     Physically protected                        
      

```

## Trust Chain

```
Root of Trust: TPM Hardware
         
          PCR Values (Platform State)
             Measured by firmware
         
          TPM Keys (Non-exportable)
             Used for signing & sealing
         
          TPM Quote (Signed Attestation)
              Binds PCR state + timestamp

Fingerprint Trust:
    Fingerprint sealed to PCR state
         
    Can only be unsealed if PCRs match
         
    Requires live TPM signing
         
    Cannot be replayed (challenge-response)
         
    Trust anchored in hardware
```

## Threat Model & Mitigations

| Threat | Mitigation |
|--------|------------|
| Fingerprint cloning | TPM-bound, requires live signing  |
| Replay attacks | Challenge-response with nonces  |
| State tampering | PCR-sealed storage  |
| Boot tampering | PCR 0-7 monitoring  |
| Firmware modification | PCR 0-1 monitoring  |
| Secure boot bypass | PCR 7 verification  |
| Credential theft | Automatic revocation on change  |
| Vault access after compromise | Automatic lockdown  |
| Log tampering | TPM-sealed audit logs  |
| Offline attacks | All trust in local TPM  |

## Performance Optimization

### Caching Strategy
```

 Memory Cache                
  
  Fingerprints (unsealed)  
  Policies (active)        
  Challenge nonces         
  

              
              

 Disk Storage                
  
  Sealed fingerprints      
  Policy definitions       
  Consequence state        
  Audit logs (sealed)      
  

              
              

 TPM Hardware (slow)         
  PCR reads: ~50ms          
  Signing: ~100ms           
  Sealing: ~100ms           

```

### Batch Operations
```python
# BAD: Multiple TPM operations
for fp_id in fingerprint_ids:
    pcrs = tpm.read_pcrs()  # 50ms each
    
# GOOD: Single TPM operation
pcrs = tpm.read_pcrs()  # 50ms once
for fp_id in fingerprint_ids:
    # Use cached PCRs
```

---

**This architecture ensures security, performance, and key innovation.**

