The design philosophy explicitly rejects the "lowest common denominator" approach typical of cross-platform APIs. Instead, KAPI embraces KERI's sophisticated security model as a non-negotiable baseline, requiring all implementations to support the full protocol rather than offering degraded compatibility modes.

Formal Specification Status

As of the latest documentation (2025), KAPI exists as a community-driven specification rather than a formal IETF RFC. However, it builds directly upon the KERI protocol specification currently progressing through IETF standardization (draft-ssmith-keri). KAPI's specification approach follows the KERI community's pattern of implementation-driven standardization, where multiple working implementations inform specification refinement rather than specification preceding implementation.

The KAPI specification explicitly references and depends upon:

• KERI Core Protocol: IETF draft-ssmith-keri for foundational identifier and event semantics
• CESR (Composable Event Streaming Representation): IETF draft-ssmith-cesr for encoding primitives
• ACDC (Authentic Chained Data Container): ToIP ACDC specification for credential structures
• OOBI (Out-Of-Band Introduction): Discovery and validation protocol for KERI identifiers
• IPEX (Issuance and Presentation Exchange): Credential exchange protocol

Version History and Evolution

KAPI's evolution tracks closely with KERI protocol maturation:

Early Phase (2020-2021): Initial KAPI concepts emerged during KERIpy development, focusing on internal component APIs within the Python reference implementation. These early APIs were tightly coupled to Python-specific patterns and not designed for cross-language interoperability.

Formalization Phase (2022-2023): The emergence of multiple KERI implementations (KERIox in Rust, KERIml in Swift) created urgent need for standardized APIs. The KERIA (KERI Agent) project drove significant KAPI design work, establishing patterns for agent-based architectures and REST API conventions. The vLEI (verifiable Legal Entity Identifier) production deployment by GLEIF provided critical real-world validation of KAPI patterns under enterprise requirements.

Current Phase (2024-2025): KAPI has matured into a comprehensive specification covering the full KERI component ecosystem. The Signify client library and KERIA server represent the current reference architecture, demonstrating KAPI's ability to support both lightweight browser-based clients and high-performance cloud agents. The specification now addresses advanced scenarios including multi-signature group identifiers, delegated identifiers, and transaction event logs for credential registries.

Protocol Architecture

Component Taxonomy

KAPI defines APIs for six primary component categories within the KERI ecosystem:

1. Controllers: Entities that manage AIDs (Autonomic Identifiers) and perform cryptographic operations. Controllers may be:

• Direct controllers: Managing keys directly on user devices
• Custodial controllers: Delegating key management to agents while retaining rotation authority
• Group controllers: Participating in multi-signature identifier management

2. Agents: Software services that act on behalf of controllers, typically providing:

• Key storage: Encrypted keystore management
• Event generation: Creating and signing key events
• Network communication: Interacting with witnesses, watchers, and other agents
• Credential management: Issuing, storing, and presenting ACDCs

The KERIA implementation exemplifies the agent architecture, exposing three distinct network interfaces:

• Boot Interface: Agent initialization and configuration
• Admin Interface: REST API for controller operations
• KERI Protocol Interface: CESR-over-HTTP for protocol-level communication

3. Witnesses: Designated entities that:

• Verify and sign key event receipts
• Maintain KERL (Key Event Receipt Log) copies
• Participate in KAACE (KERI's Agreement Algorithm for Control Establishment) consensus
• Provide availability guarantees for identifier key state

Witness APIs must support:

• Event submission and receipt generation
• OOBI resolution for identifier discovery
• Duplicity reporting mechanisms
• Witness pool coordination

4. Watchers: Validator-selected entities operating in promiscuous mode that:

• Monitor KELs for duplicity detection
• Provide independent verification of identifier key state
• Enable ambient verifiability across the ecosystem
• Support validator trust decisions

Watcher APIs emphasize:

• Passive monitoring capabilities
• Duplicity evidence collection and reporting
• First-seen policy enforcement
• Query interfaces for key state verification

5. Registrars: Entities managing transaction event logs for credential registries:

• Anchoring credential issuance/revocation events to KELs
• Maintaining TEL state for verifiable credential registries
• Providing credential status verification
• Supporting IPEX presentation exchanges

6. Verifiers: Applications and services that:

• Resolve AIDs via OOBI
• Verify KEL and KERL integrity
• Validate ACDC credentials
• Check credential status via TEL queries
• Make trust decisions based on verified data

Layering and Component Organization

KAPI implements a three-layer architecture that mirrors KERI's protocol stack:

Layer 1: Cryptographic Primitives Layer

This foundational layer provides APIs for:

• Key pair generation using cryptographic strength entropy
• Digital signature creation and verification
• Digest computation for self-addressing identifiers
• CESR encoding/decoding of cryptographic primitives

APIs at this layer must support:

• Multiple cryptographic suites (Ed25519, ECDSA secp256k1, etc.)
• Post-quantum algorithm integration
• Hardware security module (HSM) backends
• Threshold signature schemes for multisig

Layer 2: Event Processing Layer

This layer handles KERI event lifecycle:

• Inception event creation for new AIDs
• Rotation event generation for key updates
• Interaction event creation for data anchoring
• Event serialization in CESR, JSON, CBOR, or MGPK
• Event verification including signature validation and digest checking
• KEL construction and validation
• Receipt generation and verification

Layer 3: Protocol Interaction Layer

The highest layer orchestrates multi-party protocols:

• OOBI resolution for identifier discovery
• Witness coordination for event promulgation
• Watcher queries for duplicity detection
• IPEX exchanges for credential issuance/presentation
• TEL queries for credential status
• Delegation protocols for hierarchical identifiers

Data Flow and Control Flow

KAPI's data flow architecture emphasizes asynchronous, event-driven patterns that align with KERI's distributed nature:

Outbound Flow (Controller → Network):

1. Controller generates event via KAPI
2. Event signed with current signing keys
3. Event transmitted to witnesses via KAPI
4. Receipts collected asynchronously
5. KERL updated with receipted events

Inbound Flow (Network → Controller):

1. Events received from witnesses or agents
2. Events placed in escrow if dependencies missing
3. KEL validation performed
4. Duplicity checks executed
5. Valid events processed and key state updated

Query Flow (Verifier → Network):

1. OOBI resolution to discover witness endpoints
2. KEL retrieval from witnesses
3. KERL validation with receipt verification
4. Key state computation from validated KEL
5. TEL queries for credential status (if applicable)

State Management Approach

KAPI components maintain several categories of state:

Persistent State:

• KELs: Immutable append-only logs of key events
• KERLs: KELs augmented with witness receipts
• TELs: Transaction logs for credential registries
• Keystores: Encrypted storage of private keys
• ACDCs: Issued and received credentials

Ephemeral State:

• Escrow state: Out-of-order events awaiting dependencies
• Connection state: Active network connections to witnesses/agents
• Query cache: Recently resolved OOBIs and key states

Computed State:

• Key state: Current authoritative keys derived from KEL
• Witness configuration: Current witness set and thresholds
• Credential status: Derived from TEL queries

KAPI's state management follows RUN (Read, Update, Nullify) semantics rather than traditional CRUD, reflecting KERI's append-only architecture where events are never deleted, only superseded.

Message Formats & Encoding

CESR as Universal Encoding

KAPI mandates CESR (Composable Event Streaming Representation) as the canonical encoding for all KERI protocol messages. CESR provides:

Dual-Domain Encoding: Messages can be represented in either:

• Text domain: Base64 URL-safe encoding for human readability and JSON compatibility
• Binary domain: Compact binary encoding for efficient network transmission
• Round-trip composability: Lossless conversion between domains while preserving primitive boundaries

Self-Framing Primitives: Each CESR primitive includes:

• Derivation code: Identifies cryptographic algorithm and primitive type
• Length information: Enables stream parsing without external framing
• Value: The actual cryptographic material (key, signature, digest)

Group Codes: CESR supports count codes that frame groups of primitives, enabling:

• Efficient pipelining of multiple primitives
• Attachment of signatures and receipts to events
• Nested encoding of complex structures

Core Message Types

KAPI defines several fundamental message categories:

1. Key Event Messages

All key events share a common structure:

{
  "v": "KERI10JSON00011c_",  // Version string
  "t": "icp",                 // Event type (ilk)
  "d": "EBabiu_JCkE0GbiglDX...", // Event SAID
  "i": "EBabiu_JCkE0GbiglDX...", // Identifier prefix
  "s": "0",                   // Sequence number
  "kt": "1",                  // Signing threshold
  "k": ["DaU6JR2nmwyZ-i0d8..."], // Current keys
  "nt": "1",                  // Next threshold
  "n": ["EQb3zXwY6QGZqGx9..."], // Next key digests
  "bt": "2",                  // Witness threshold
  "b": ["BGKVzj4ve0VSd8z_..."], // Witness identifiers
  "c": [],                    // Configuration traits
  "a": []                     // Anchored data seals
}

Field Semantics:

• v: Version string specifying KERI version and serialization format
• t: Event type (ilk) - icp (inception), rot (rotation), ixn (interaction), dip (delegated inception), drt (delegated rotation)
• d: SAID (Self-Addressing Identifier) of the event
• i: AID prefix being managed
• s: Sequence number (hexadecimal string)
• kt: Current threshold for signing
• k: List of current public keys (qualified CESR primitives)
• nt: Next threshold for rotation
• n: List of next key digests (cryptographic commitments)
• bt: Witness threshold (TOAD)
• b: List of witness AIDs
• c: Configuration traits (optional features)
• a: Seals anchoring external data

2. Receipt Messages

Receipts provide witness attestation:

{
  "v": "KERI10JSON00011c_",
  "t": "rct",
  "d": "EBabiu_JCkE0GbiglDX...", // Event being receipted
  "i": "BGKVzj4ve0VSd8z_..."  // Witness identifier
}

Receipts are typically transmitted with indexed signatures attached via CESR count codes.

3. OOBI Messages

Out-Of-Band Introductions enable identifier discovery:

URL Format:

http://witness.example.com/oobi/EBabiu_JCkE0GbiglDX.../witness/BGKVzj4ve0VSd8z_...

JSON Format:

{
  "eid": "EBabiu_JCkE0GbiglDX...",  // Identifier
  "scheme": "http",
  "url": "http://witness.example.com:5642/",
  "role": "witness"  // or "controller", "watcher", etc.
}

4. IPEX Messages

Issuance and Presentation Exchange messages use KERI exchange events:

{
  "v": "KERI10JSON00011c_",
  "t": "exn",
  "d": "EBabiu_JCkE0GbiglDX...",
  "i": "EBabiu_JCkE0GbiglDX...",  // Sender AID
  "p": "",                        // Prior event digest
  "dt": "2024-01-15T10:30:00.000000+00:00",
  "r": "/ipex/grant",             // Route
  "q": {},                        // Query parameters
  "a": {                          // Payload
    "m": "Grant message",
    "acdc": { /* ACDC credential */ }
  }
}

5. TEL Messages

Transaction Event Log messages track credential status:

{
  "v": "KERI10JSON00011c_",
  "t": "iss",  // Issuance event
  "d": "EBabiu_JCkE0GbiglDX...",
  "i": "EBabiu_JCkE0GbiglDX...",  // Registry identifier
  "s": "0",
  "ri": "EQb3zXwY6QGZqGx9...",   // Credential SAID
  "dt": "2024-01-15T10:30:00.000000+00:00"
}

Serialization Formats

KAPI supports multiple serialization formats via CESR interleaving:

JSON: Human-readable, widely supported

• Used for REST APIs and debugging
• CESR attachments encoded as Base64 strings
• Field ordering must be deterministic for SAID computation

CBOR: Compact binary format

• Efficient for network transmission
• Maintains CESR composability
• Preferred for high-throughput scenarios

MessagePack: Alternative binary format

• Similar efficiency to CBOR
• Broader language support in some ecosystems

Pure CESR: Native KERI encoding

• Maximum compactness
• Optimal for witness communication
• Requires CESR-aware parsers

Attachment Patterns

KAPI uses CESR count codes to attach signatures and receipts:

Signature Attachment:

{event_json}-AABAABabiu_JCkE0GbiglDX...  // Indexed signature

Receipt Attachment:

{event_json}-VAS-GAB0AAAAAAAAAAAAAAAAAAAAABabiu...  // Receipt with witness signature

Multiple Attachments:

{event_json}-AABAABabiu...-AABAAQb3zX...-VAS-GAB0AA...  // Multiple signatures and receipt

This attachment pattern enables pipelining where multiple events with attachments can be concatenated in a single stream while maintaining individual event boundaries.

Protocol Mechanics

Identifier Inception Flow

Creating a new AID involves coordinated API calls:

1. Key Generation

API: generate_keypairs(count=1, next_count=1, algorithm="Ed25519")
Returns: {
  "current": [{"public": "...", "private": "..."}],
  "next": [{"public": "...", "private": "..."}]
}

2. Inception Event Creation

API: create_inception(
  keys=["DaU6JR2nmwyZ..."],
  next_digests=["EQb3zXwY6QGZ..."],
  witnesses=["BGKVzj4ve0VSd8z_...", ...],
  witness_threshold=2
)
Returns: {
  "event": {/* inception event */},
  "prefix": "EBabiu_JCkE0GbiglDX..."
}

3. Event Signing

API: sign_event(event, private_keys)
Returns: {
  "event": {/* event */},
  "signatures": ["AABabiu_JCkE0GbiglDX..."]
}

4. Witness Promulgation

API: send_to_witnesses(signed_event, witness_endpoints)
Returns: {
  "receipts": [{/* receipt from witness 1 */}, ...],
  "threshold_met": true
}

5. KEL Storage

API: store_event(event, signatures, receipts)
Returns: {"stored": true, "sequence": "0"}

Key Rotation Flow

Rotation events update key state:

1. Generate New Keys

API: generate_keypairs(count=1, next_count=1)

2. Create Rotation Event

API: create_rotation(
  identifier="EBabiu_JCkE0GbiglDX...",
  sequence="1",
  previous_digest="EBabiu_JCkE0GbiglDX...",
  keys=["DnewKey123..."],
  next_digests=["EnextKey456..."],
  witnesses=[...],  // Can change witness set
  witness_threshold=2,
  witness_adds=[],  // New witnesses
  witness_cuts=[]   // Removed witnesses
)

3. Sign with Pre-Rotated Keys

API: sign_event(rotation_event, pre_rotated_private_keys)

Critical: Rotation events MUST be signed with the pre-rotated keys committed in the previous event, not the current signing keys.

4. Promulgate and Receipt

API: send_to_witnesses(signed_rotation)

Multi-Signature Coordination

Group multi-sig identifiers require coordination:

1. Participant Setup Each participant creates their own AID and exchanges OOBIs.

2. Group Inception

API: create_group_inception(
  participants=[
    {"aid": "EParticipant1...", "weight": "1"},
    {"aid": "EParticipant2...", "weight": "1"}
  ],
  threshold="2",  // 2-of-2 multisig
  witnesses=[...]
)

3. Signature Collection Each participant signs the group inception event:

API: sign_event(group_inception, participant_private_key)

Signatures are collected until threshold is met.

4. Event Finalization

API: finalize_multisig_event(
  event=group_inception,
  signatures=[sig1, sig2]
)

5. Witness Promulgation Once threshold signatures are collected, the event is sent to witnesses.

OOBI Resolution Protocol

OOBI resolution enables identifier discovery:

1. OOBI Reception

API: receive_oobi(
  "http://witness.example.com/oobi/EBabiu_JCkE0GbiglDX.../witness/BGKVzj4ve0VSd8z_..."
)

2. Endpoint Discovery KAPI parses the OOBI to extract:

• Target AID: EBabiu_JCkE0GbiglDX...
• Witness AID: BGKVzj4ve0VSd8z_...
• Endpoint URL: http://witness.example.com

3. KEL Retrieval

API: fetch_kel(
  identifier="EBabiu_JCkE0GbiglDX...",
  endpoint="http://witness.example.com"
)
Returns: {"kel": [{/* inception */}, {/* rotation */}, ...]}

4. KEL Validation

API: validate_kel(kel)
Returns: {
  "valid": true,
  "key_state": {/* current key state */}
}

5. Caching Validated key state is cached for future use.

IPEX Credential Exchange

IPEX orchestrates credential issuance and presentation:

Issuance Flow:

1. Credential Creation

API: create_acdc(
  issuer="EIssuer123...",
  issuee="EIssuee456...",
  schema="ESchema789...",
  attributes={/* credential data */}
)

2. Grant Message

API: create_ipex_grant(
  sender="EIssuer123...",
  recipient="EIssuee456...",
  acdc={/* credential */}
)

3. Transmission

API: send_ipex_message(grant_message, recipient_endpoint)

Presentation Flow:

1. Presentation Request

API: create_ipex_apply(
  sender="EVerifier123...",
  recipient="EHolder456...",
  schema="ESchema789..."  // Requested credential type
)

2. Credential Selection

API: select_credentials(
  schema="ESchema789...",
  holder="EHolder456..."
)
Returns: [{/* matching credentials */}]

3. Presentation Creation

API: create_ipex_offer(
  sender="EHolder456...",
  recipient="EVerifier123...",
  acdc={/* selected credential */}
)

4. Verification

API: verify_presentation(
  presentation={/* IPEX offer */}
)
Returns: {
  "valid": true,
  "issuer_verified": true,
  "holder_verified": true,
  "not_revoked": true
}

TEL Status Queries

Transaction Event Logs track credential status:

1. Registry Discovery

API: resolve_registry(
  credential_said="ECredential123..."
)
Returns: {
  "registry_aid": "ERegistry456...",
  "backers": ["EBacker1...", "EBacker2..."]
}

2. Status Query

API: query_credential_status(
  credential_said="ECredential123...",
  registry_aid="ERegistry456..."
)
Returns: {
  "status": "issued",  // or "revoked"
  "issued_at": "2024-01-15T10:30:00Z",
  "revoked_at": null
}

3. TEL Verification

API: verify_tel(
  tel=[{/* issuance event */}, ...],
  registry_aid="ERegistry456..."
)
Returns: {"valid": true}

Security Properties

Threat Model

KAPI's security design addresses multiple threat categories:

1. Network Adversaries

• Man-in-the-middle attacks: Mitigated by end-to-end signatures on all events
• Replay attacks: Prevented by sequence numbers and SAID uniqueness
• Message tampering: Detected via cryptographic digests

2. Compromised Components

• Malicious witnesses: Detected via duplicity detection and first-seen policy
• Compromised agents: Limited by custodial rotation separating signing authority from rotation authority
• Rogue watchers: Cannot forge events, only report observed duplicity

3. Key Compromise

• Current key compromise: Mitigated by pre-rotation enabling recovery
• Pre-rotated key compromise: Requires compromise of unexposed keys (post-quantum secure)
• Witness collusion: Requires exceeding TOAD threshold

Security Guarantees

KAPI preserves KERI's core security properties:

1. Self-Certifying Identifiers

• Identifiers are cryptographically bound to key pairs
• No trusted third party required for identifier-to-key binding
• Autonomic control over identifier namespace

2. End-to-End Verifiability

• All events are digitally signed by controlling keys
• KELs are append-only and hash-chained
• Receipts provide non-repudiable witness attestation

3. Duplicity Detection

• First-seen policy enables detection of conflicting events
• Watchers provide ambient verifiability
• Duplicity evidence is cryptographically provable

4. Key Rotation Security

• Pre-rotation provides post-quantum security
• Rotation keys are one-time use
• Compromise of current keys doesn't compromise future keys

5. Witness Agreement

• KAACE algorithm ensures Byzantine fault tolerance
• TOAD threshold prevents single witness compromise
• Witness pools are controller-managed and rotatable

Attack Resistance

KAPI's design resists specific attack vectors:

Live Attacks

• Compromise of current signing keys
• Mitigated by pre-rotation enabling recovery via unexposed rotation keys
• Requires attacker to compromise both current and pre-rotated keys simultaneously

Dead Attacks

• Attacks on stale key state
• Prevented by first-seen policy at witnesses
• Historical events cannot be altered after witnessing

Eclipse Attacks

• Isolating a controller from honest witnesses
• Mitigated by watcher networks providing independent verification
• OOBI resolution enables discovery of alternative endpoints

Sybil Attacks

• Creating multiple fake identities
• Limited impact due to reputation and trust being tied to specific AIDs
• Witness selection is controller-managed, not network-wide

Replay Attacks

• Retransmitting valid events
• Prevented by sequence numbers and SAID uniqueness
• Witnesses reject duplicate events

Interoperability

Dependencies on KERI/ACDC Protocols

KAPI is fundamentally dependent on the KERI protocol stack:

KERI Core Protocol

• Defines AID structure and semantics
• Specifies key event types and validation rules
• Establishes KEL and KERL data structures
• Mandates pre-rotation and witness mechanisms

CESR Encoding

• Provides universal encoding for cryptographic primitives
• Enables dual-domain text/binary representation
• Supports composability and pipelining

ACDC Credentials

• Defines verifiable credential structure
• Specifies chaining and selective disclosure mechanisms
• Establishes schema and rule semantics

OOBI Discovery

• Enables out-of-band identifier discovery
• Provides endpoint resolution for witnesses and agents
• Supports percolated discovery patterns

IPEX Exchange

• Orchestrates credential issuance and presentation
• Defines grant, apply, offer message patterns
• Enables graduated disclosure workflows

TEL Registries

• Tracks credential issuance and revocation status
• Anchors credential lifecycle events to KELs
• Provides verifiable credential registry functionality

Integration Points

KAPI provides integration with external systems:

DID Methods

• did:keri: Native KERI DID method
• did:webs: Web-based KERI identifiers with KERI event streams
• DID resolution to KERI AIDs

Verifiable Credential Standards

• W3C VC Data Model compatibility via ACDC
• JSON-LD context support (optional)
• Verifiable Presentations via IPEX

Transport Protocols

• HTTP/HTTPS for REST APIs
• WebSockets for real-time event streaming
• TCP for direct peer-to-peer communication
• QUIC for low-latency scenarios

Storage Backends

• LMDB (Lightning Memory-Mapped Database) for high-performance local storage
• SQL databases for enterprise deployments
• Cloud storage for agent services

Cryptographic Libraries

• libsodium for Ed25519 and X25519
• OpenSSL for ECDSA and RSA
• Post-quantum libraries for future-proof algorithms

Implementation Considerations

Common Challenges

1. Asynchronous Event Processing

KERI's distributed nature requires handling out-of-order events:

• Events may arrive before their dependencies
• Escrow mechanisms must queue events until dependencies resolve
• Timeout policies needed for abandoned event sequences

2. Witness Coordination

Coordinating with multiple witnesses introduces complexity:

• Receipt collection must handle partial failures
• TOAD threshold satisfaction requires tracking receipt counts
• Witness rotation must maintain continuity

3. Key Management

Secure key storage is critical:

• Private keys must be encrypted at rest
• Pre-rotated keys require secure backup
• Multi-signature scenarios need distributed key management

4. State Synchronization

Maintaining consistent key state across components:

• KEL updates must be atomic
• Duplicity detection requires comparing multiple KEL versions
• Watcher queries may return stale data

5. Performance Optimization

Balancing security with performance:

• Signature verification is computationally expensive
• KEL validation requires processing entire event history
• CESR parsing must be efficient for high-throughput scenarios

Performance Considerations

Signature Operations

• Ed25519 signatures: ~15,000 signatures/second (single core)
• Signature verification: ~40,000 verifications/second (single core)
• Batch verification can improve throughput

KEL Processing

• Inception events: ~1ms processing time
• Rotation events: ~2ms (includes pre-rotation validation)
• Interaction events: ~0.5ms (no key state changes)

Network Latency

• Witness promulgation: 50-200ms (depends on witness count and network)
• OOBI resolution: 100-500ms (includes KEL retrieval and validation)
• TEL queries: 50-150ms (cached registry state)

Storage Requirements

• KEL size: ~500 bytes per event (average)
• KERL size: ~1KB per event (includes receipts)
• ACDC size: 1-10KB (depends on attributes)

Scalability Patterns

Horizontal Scaling

• Witness pools can be distributed geographically
• Watcher networks scale independently
• Agent services can be load-balanced

Caching Strategies

• Key state caching reduces KEL reprocessing
• OOBI resolution results can be cached
• TEL status queries benefit from registry state caching

Batching Operations

• Multiple events can be pipelined in single CESR stream
• Signature verification can be batched
• Witness promulgation can send multiple events simultaneously

Security Best Practices

Key Generation

• Use cryptographic strength entropy sources
• Generate keys in trusted execution environments when possible
• Implement key stretching for password-derived keys

Key Storage

• Encrypt keystores with strong passphrases
• Use hardware security modules for high-value identifiers
• Implement secure backup and recovery procedures

Network Security

• Use TLS for all network communication
• Validate witness and agent AIDs via OOBI
• Implement rate limiting and DDoS protection

Operational Security

• Regularly rotate witnesses to prevent long-term compromise
• Monitor for duplicity via watcher networks
• Implement incident response procedures for key compromise

Testing Strategies

Unit Testing

• Test key event creation and validation
• Verify CESR encoding/decoding
• Validate signature operations

Integration Testing

• Test witness coordination and receipt collection
• Verify OOBI resolution workflows
• Validate IPEX credential exchanges

Security Testing

• Test duplicity detection mechanisms
• Verify key rotation security
• Validate witness threshold enforcement

Performance Testing

• Benchmark KEL processing throughput
• Measure witness promulgation latency
• Test scalability under load

Deployment Patterns

Client-Side Deployment

• Signify browser extension for web applications
• Mobile wallet apps for iOS/Android
• Desktop applications with local keystores

Server-Side Deployment

• KERIA cloud agents for enterprise use
• Witness services for identifier infrastructure
• Watcher networks for duplicity detection

Hybrid Deployment

• Custodial agents with partial rotation
• Delegated identifiers for organizational hierarchies
• Multi-signature coordination across devices

Conclusion

KAPI represents a comprehensive API framework specifically designed to preserve and propagate KERI's revolutionary security properties across distributed components. By mandating CESR encoding, supporting asynchronous event processing, and enabling witness coordination, KAPI provides the essential infrastructure for building secure, scalable, and interoperable KERI-based applications.

The API's design reflects KERI's core philosophy: cryptographic security should not be compromised for convenience. Every KAPI endpoint, message format, and interaction pattern maintains KERI's guarantees around self-certifying identifiers, key event log integrity, duplicity detection, and end-to-end verifiability.

As the KERI ecosystem continues to mature, KAPI will evolve to support new use cases while maintaining backward compatibility and security guarantees. The specification's implementation-driven approach ensures that KAPI remains practical and deployable while advancing the state of decentralized identity infrastructure.

Testing Requirements

KAPI implementations should include comprehensive test suites:

Protocol Compliance Tests:

• Verify CESR encoding correctness
• Validate event structure and signatures
• Test KEL validation logic
• Confirm witness threshold enforcement

Security Tests:

• Test duplicity detection mechanisms
• Verify key rotation security
• Validate pre-rotation enforcement
• Test attack resistance (replay, eclipse, etc.)

Integration Tests:

• Test witness coordination workflows
• Verify OOBI resolution
• Validate IPEX credential exchanges
• Test TEL status queries

Performance Tests:

• Benchmark KEL processing throughput
• Measure witness promulgation latency
• Test scalability under load
• Profile memory usage patterns

Deployment Considerations

Client-Side Deployments:

• Minimize key exposure by using secure enclaves
• Implement proper keystore encryption
• Support offline operation where possible
• Provide clear user consent flows

Server-Side Deployments:

• Implement rate limiting and DDoS protection
• Use TLS for all network communication
• Deploy witness services with geographic distribution
• Monitor for duplicity via watcher networks

Hybrid Deployments:

• Use custodial rotation for agent-based architectures
• Implement partial rotation for split authority
• Support delegated identifiers for organizational hierarchies
• Enable multi-signature coordination across devices

Common Pitfalls

1. Improper Key Management: Never store private keys unencrypted or transmit them over networks.

2. Ignoring Asynchronous Nature: Don't assume events arrive in order; implement proper escrow mechanisms.

3. Weak Witness Coordination: Ensure TOAD thresholds are properly enforced and receipts are validated.

4. Inadequate Duplicity Detection: Always check for conflicting events via watcher queries.

5. Performance Shortcuts: Don't skip signature verification or KEL validation for performance; use caching instead.

Future Directions

KAPI will continue evolving to support:

• Post-quantum cryptographic algorithms
• Enhanced privacy features (zero-knowledge proofs)
• Improved scalability patterns
• Additional transport protocols
• Extended credential types and schemas

Developers should monitor the KAPI GitHub repository for specification updates and participate in the KERI community to influence future development.