CESR Encoding Structure

Delegated rotation events utilize CESR's qualified cryptographic primitives:

Event Structure (CESR):
┌─────────────────┬──────────────────┬─────────────────┐
│ Count Code      │ Event Data       │ Signatures      │
│ (4 chars)       │ (variable)       │ (variable)      │
└─────────────────┴──────────────────┴─────────────────┘

Signature Attachment:
┌─────────────────┬──────────────────┬─────────────────┐
│ Counter Code    │ Indexed Sigs     │ Witness Receipts│
│ -AAB (indexed)  │ (88 chars each)  │ (optional)      │
└─────────────────┴──────────────────┴─────────────────┘

Protocol Mechanics

Cooperative Delegation Workflow

1. Delegate Initiation: Delegate creates unsigned drt event with new key material
2. Threshold Validation: Verify current keys satisfy rotation authority from prior event
3. Pre-rotation Commitment: Generate cryptographic digests of next rotation keys
4. Signature Generation: Current controlling keys sign the rotation event
5. Delegator Anchoring: Delegator creates interaction event with delegation seal
6. Witness Promulgation: Witnesses validate and sign the rotation event
7. KEL Integration: Event becomes part of the delegated identifier's verifiable log

State Transition Validation

def validate_drt_transition(prior_event, drt_event, delegator_kel):
    # Verify sequence progression
    assert drt_event.s == prior_event.s + 1
    
    # Verify prior event digest
    assert drt_event.p == compute_digest(prior_event)
    
    # Verify key threshold satisfaction
    assert len(drt_event.k) >= int(drt_event.kt)
    
    # Verify pre-rotation commitment
    assert len(drt_event.n) >= int(drt_event.nt)
    
    # Verify delegator anchoring
    delegation_seal = find_delegation_seal(delegator_kel, drt_event.d)
    assert delegation_seal is not None
    
    return True

Cryptographic Foundation

Digital Signature Verification

Delegated rotation events require multi-party cryptographic validation:

1. Delegate Signatures: Current controlling keys must satisfy threshold
2. Witness Signatures: Witness pool must satisfy backer threshold
3. Delegator Anchoring: Cryptographic seal in delegator's KEL

Pre-rotation Security Model

The n field contains Blake3-256 digests of pre-rotated key pairs:

for each next_key in rotation_set:
    key_digest = Blake3_256(next_key.public_bytes)
    n_array.append(CESR_encode(key_digest))

This provides post-quantum security by cryptographically committing to keys that remain unexposed until the subsequent rotation event.

Threshold Cryptography

KERI supports both numeric and fractional thresholds:

• Numeric: "3" requires exactly 3 signatures
• Fractional: "2/3" requires 2 signatures from a 3-key set
• Weighted: Future extension for weighted threshold schemes

Implementation Specifications

Event Creation Algorithm

def create_drt_event(delegated_aid, new_keys, next_keys, delegator_aid, 
                     witness_config=None, anchors=None):
    """
    Create delegated rotation event with proper field ordering
    """
    prior_event = get_latest_establishment_event(delegated_aid)
    
    event = {
        "v": KERI_VERSION,
        "t": "drt",
        "d": "",  # Placeholder for SAID computation
        "i": delegated_aid,
        "s": prior_event["s"] + 1,
        "p": compute_digest(prior_event),
        "kt": str(len(new_keys)),  # Simplified threshold
        "k": [key.qb64 for key in new_keys],
        "nt": str(len(next_keys)),
        "n": [compute_digest(key.qb64b) for key in next_keys],
        "di": delegator_aid
    }
    
    # Add witness configuration if provided
    if witness_config:
        event.update(witness_config)
    
    # Add anchoring seals if provided
    if anchors:
        event["a"] = anchors
    
    # Compute SAID
    event["d"] = compute_said(event)
    
    return event

Validation State Machine

class DRTValidator:
    def __init__(self, delegated_kel, delegator_kel):
        self.delegated_kel = delegated_kel
        self.delegator_kel = delegator_kel
        
    def validate(self, drt_event):
        """Comprehensive DRT event validation"""
        
        # Phase 1: Structural validation
        self._validate_structure(drt_event)
        
        # Phase 2: Sequence validation
        self._validate_sequence(drt_event)
        
        # Phase 3: Cryptographic validation
        self._validate_signatures(drt_event)
        
        # Phase 4: Delegation validation
        self._validate_delegation_authority(drt_event)
        
        # Phase 5: Witness validation
        self._validate_witness_consensus(drt_event)
        
        return ValidationResult.VALID

Performance Characteristics

Computational Complexity

• Event Creation: O(k) where k = number of keys
• Signature Verification: O(t) where t = threshold requirement
• KEL Validation: O(n) where n = sequence length
• Delegation Verification: O(log d) where d = delegator KEL length

Storage Requirements

• Base Event Size: ~500-800 bytes (JSON serialization)
• CESR Encoded: ~400-600 bytes (binary optimized)
• Signature Attachment: 88 bytes per signature
• Witness Receipts: 88 bytes per witness signature

Technical Relationships

Integration with KERI Event Types

graph TD
    A[dip - Delegated Inception] --> B[drt - Delegated Rotation]
    B --> C[drt - Subsequent Rotation]
    B --> D[ixn - Interaction Event]
    E[Delegator ixn] --> B
    B --> F[Witness Receipts]
    B --> G[Watcher Confirmations]

Relationship to ACDC Credentials

Delegated rotation events can anchor ACDC credential operations:

{
  "a": [
    {
      "i": "credential_registry_AID",
      "s": "0",
      "d": "credential_event_digest"
    }
  ]
}

CESR Stream Integration

DRT events integrate seamlessly into CESR streams for efficient processing:

CESR Stream Format:
{"v":"KERI10JSON00011c_","t":"drt",...}-AABAA{signatures}

Edge Cases & Error Handling

Failure Modes

Insufficient Delegation Authority

class InsufficientDelegationAuthority(KERIError):
    """Raised when delegator hasn't properly anchored rotation"""
    def __init__(self, delegated_aid, delegator_aid):
        self.message = f"No delegation seal found in {delegator_aid} for {delegated_aid}"

Threshold Violation

class ThresholdViolation(KERIError):
    """Raised when signature threshold not satisfied"""
    def __init__(self, required, provided):
        self.message = f"Required {required} signatures, got {provided}"

Sequence Gap Detection

def detect_sequence_gaps(kel):
    """Detect missing events in KEL sequence"""
    sequences = [event["s"] for event in kel]
    expected = list(range(len(kel)))
    gaps = set(expected) - set(sequences)
    if gaps:
        raise SequenceGapError(f"Missing sequences: {gaps}")

Recovery Procedures

Delegator Unavailability

When delegator is unavailable for anchoring:

1. Escrow Mode: Hold rotation event in escrow until delegator returns
2. Emergency Rotation: Use pre-established emergency delegation paths
3. Witness Override: Implement witness-based emergency procedures (if configured)

Key Compromise Recovery

def emergency_rotation(compromised_aid, recovery_keys, delegator_signature):
    """Emergency rotation for compromised delegated AID"""
    
    # Create emergency rotation event
    emergency_drt = {
        "v": KERI_VERSION,
        "t": "drt",
        "i": compromised_aid,
        "emergency": True,  # Special flag
        "k": recovery_keys,
        "di": delegator_aid
    }
    
    # Require delegator signature for emergency rotation
    validate_delegator_signature(emergency_drt, delegator_signature)
    
    return emergency_drt

Standards & Specifications

KERI Protocol Compliance

DRT events must comply with:

• KERI Core Specification: Event structure and validation rules
• CESR Specification: Encoding and streaming requirements
• SAID Specification: Self-addressing identifier computation

Version Compatibility Matrix

Interoperability Requirements

• Cross-Implementation: Must work across KERIpy, KERI-Ox, KERIA
• Transport Agnostic: HTTP, WebSocket, direct exchange
• Serialization: JSON, CBOR, MessagePack support

Production Considerations

Deployment Architecture

Delegated Identity Service:
  components:
    - delegate_controller: Manages delegated AIDs
    - delegator_interface: Communicates with delegating authority
    - witness_network: Provides consensus and availability
    - watcher_service: Monitors for duplicity
    
  scaling:
    - horizontal: Multiple delegate controllers
    - vertical: Increased witness pool size
    - geographic: Distributed witness deployment

Monitoring and Observability

Key Metrics

• Rotation Latency: Time from initiation to completion
• Delegation Confirmation Rate: Success rate of delegator anchoring
• Witness Consensus Time: Time to achieve witness threshold
• KEL Validation Performance: Event processing throughput

Alerting Conditions

ALERT_CONDITIONS = {
    "delegation_timeout": "No delegator anchoring within 24 hours",
    "witness_unavailable": "Witness threshold not achievable",
    "sequence_gap": "Missing events detected in KEL",
    "duplicity_detected": "Conflicting rotation events found"
}

Security Hardening

Key Management

• Hardware Security Modules: Store rotation keys in HSMs
• Multi-Party Computation: Distribute key generation across parties
• Threshold Signatures: Implement BLS or Schnorr threshold schemes

Network Security

• TLS 1.3: Encrypt all delegation communications
• Certificate Pinning: Pin delegator and witness certificates
• Rate Limiting: Prevent rotation spam attacks

Operational Security

• Audit Logging: Log all rotation attempts and outcomes
• Access Controls: Restrict rotation authority to authorized operators
• Incident Response: Procedures for handling key compromise

Security Best Practices

Key Material Protection

class SecureDRTSigner:
    """Secure signing for delegated rotation events"""
    
    def __init__(self, hsm_interface):
        self.hsm = hsm_interface
        self.signing_policy = SigningPolicy()
    
    def sign_drt_event(self, event, key_identifiers):
        """Sign drt event with HSM-protected keys"""
        
        # Verify signing authorization
        self.signing_policy.authorize_rotation(event, key_identifiers)
        
        # Generate signatures using HSM
        signatures = []
        for key_id in key_identifiers:
            signature = self.hsm.sign(
                key_id=key_id,
                data=event['d'].encode('utf-8'),
                algorithm='Ed25519'
            )
            signatures.append(signature)
        
        return signatures

Delegator Verification

def verify_delegator_authority(drt_event, delegator_kel):
    """Comprehensive delegator authority verification"""
    
    # Verify delegator AID is valid
    if not validate_aid_format(drt_event['di']):
        raise SecurityError("Invalid delegator AID format")
    
    # Verify delegator KEL integrity
    if not verify_kel_integrity(delegator_kel):
        raise SecurityError("Delegator KEL integrity compromised")
    
    # Verify delegation seal exists and is properly signed
    seal = find_delegation_seal(delegator_kel, drt_event['d'])
    if not seal:
        raise SecurityError("No delegation seal found")
    
    # Verify seal signature with current delegator keys
    current_keys = get_current_keys(delegator_kel)
    if not verify_seal_signature(seal, current_keys):
        raise SecurityError("Invalid delegation seal signature")
    
    return True

Testing Strategies

Property-Based Testing

from hypothesis import given, strategies as st

@given(
    sequence=st.integers(min_value=1, max_value=1000),
    key_count=st.integers(min_value=1, max_value=10),
    threshold=st.integers(min_value=1, max_value=10)
)
def test_drt_event_properties(sequence, key_count, threshold):
    """Property-based testing for drt events"""
    
    # Ensure threshold doesn't exceed key count
    threshold = min(threshold, key_count)
    
    # Generate test event
    drt_event = generate_test_drt(
        sequence=sequence,
        key_count=key_count,
        threshold=threshold
    )
    
    # Verify invariants
    assert int(drt_event['kt']) <= len(drt_event['k'])
    assert int(drt_event['nt']) <= len(drt_event['n'])
    assert int(drt_event['s']) == sequence
    assert drt_event['t'] == 'drt'

Integration Testing

class DRTIntegrationTest:
    """End-to-end testing for delegated rotation"""
    
    def test_full_delegation_lifecycle(self):
        """Test complete delegation from inception to rotation"""
        
        # Setup delegator and delegate
        delegator = create_test_aid()
        delegate = create_delegated_aid(delegator)
        
        # Perform rotation
        new_keys = generate_key_pairs(2)
        drt_event = create_drt_event(delegate, new_keys, delegator)
        
        # Verify rotation success
        assert validate_drt_event(drt_event)
        assert get_current_keys(delegate) == new_keys
        
        # Verify KEL integrity
        assert verify_kel_integrity(delegate.kel)