Handshake API

createChallenge

Creates a challenge message with a random nonce for the trust handshake.

function createChallenge(options: { from: string }): ChallengeMessage

Parameters

Returns

ChallengeMessage

Example

import { createChallenge } from "@credat/sdk";
 
const challenge = createChallenge({ from: "did:web:service.com" });
// {
//   type: "credat:challenge",
//   nonce: "dG9rZW4tMTIz...",
//   from: "did:web:service.com",
//   timestamp: "2026-02-24T10:00:00.000Z"
// }

presentCredentials

Creates a presentation message: the agent signs the challenge nonce and attaches its delegation credential.

function presentCredentials(options: PresentOptions): Promise<PresentationMessage>

Parameters

PresentOptions

Returns

PresentationMessage

Example

import { presentCredentials } from "@credat/sdk";
 
const presentation = await presentCredentials({
  challenge,
  delegation: delegation.token,
  agent,
});

verifyPresentation

Verifies a complete presentation: nonce proof, agent identity, and delegation credential.

function verifyPresentation(
  presentation: PresentationMessage,
  options: VerifyPresentationOptions,
): Promise<DelegationResult>

Parameters

VerifyPresentationOptions

Returns

DelegationResult --- same shape as verifyDelegation. See Delegation API.

Verification steps

1. Nonce match --- Presentation nonce matches the challenge nonce
2. Nonce proof --- Agent’s signature over the nonce is valid (proves identity)
3. Delegation --- The delegation VC is valid, signed by the owner, and not expired

If any step fails, the function returns early with the relevant error.

Algorithm detection

If agentAlgorithm is not specified, it’s inferred from the public key:

• 33 bytes -> ES256 (P-256 compressed)
• 32 bytes -> EdDSA (Ed25519)

Example

import { verifyPresentation } from "@credat/sdk";
 
const result = await verifyPresentation(presentation, {
  challenge,
  ownerPublicKey: ownerKeyPair.publicKey,
  agentPublicKey: agent.keyPair.publicKey,
});
 
if (result.valid) {
  console.log(result.agent);   // Agent DID
  console.log(result.owner);   // Owner DID
  console.log(result.scopes);  // Granted scopes
}

Errors in result

Message types

All three message types are exported as TypeScript types:

import type {
  ChallengeMessage,
  PresentationMessage,
  AckMessage,
  HandshakeMessage, // Union of all three
} from "@credat/sdk";

AckMessage

The acknowledgment message sent after verification. This is a convenience type --- Credat does not generate it automatically.