> ## Documentation Index > Fetch the complete documentation index at: https://docs.portalhq.io/llms.txt > Use this file to discover all available pages before exploring further. # Create a presignature > Pre-computes MPC signing data for faster subsequent transaction signing. Each presignature can only be used once. You can have up to 100 active presignatures per client. Presignatures currently only support the `SECP256K1` curve (EVM, Bitcoin). ED25519 (Solana) support is coming soon. ## OpenAPI ````yaml /openapi/enclave-mpc-api.yaml post /v1/presign/{curve} openapi: 3.1.0 info: title: Portal Enclave MPC API version: '1.0' description: | The Enclave MPC API provides endpoints for MPC wallet generation, signing, backup, and recovery. All endpoints require a Client API Key or Client Session Token as a Bearer token. ## Base URL `https://mpc-client.portalhq.io` servers: - url: https://mpc-client.portalhq.io security: - bearerAuth: [] tags: - name: MPC Operations description: MPC wallet generation, signing, asset transfers, backup, and recovery paths: /v1/presign/{curve}: post: tags: - MPC Operations summary: Create a presignature description: > Pre-computes MPC signing data for faster subsequent transaction signing. Each presignature can only be used once. You can have up to 100 active presignatures per client. Presignatures currently only support the `SECP256K1` curve (EVM, Bitcoin). ED25519 (Solana) support is coming soon. operationId: presign parameters: - $ref: '#/components/parameters/Curve' - $ref: '#/components/parameters/IdempotencyKey' requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/PresignRequest' examples: clientStored: summary: Client-stored presignature value: share: eyJjbG... portalManaged: summary: Portal-managed presignature value: share: eyJjbG... managed: true responses: '200': description: Presignature created successfully content: application/json: schema: $ref: '#/components/schemas/PresignResponse' examples: clientStored: summary: Client-stored presignature value: id: expiresAt: '2025-03-18T10:00:00Z' data: portalManaged: summary: Portal-managed presignature value: id: expiresAt: '2025-03-18T10:00:00Z' '400': description: Bad request content: application/json: schema: $ref: '#/components/schemas/MpcErrorResponse' example: id: BAD_REQUEST message: Can't parse the request body '401': description: Unauthorized content: text/plain: schema: type: string example: Incorrect API key format '409': description: | Portal-managed presign request with this idempotency key is either still in progress or previously failed before activation. When the original attempt is still in progress, the response includes a `Retry-After` header; a 409 without `Retry-After` means the previous attempt has failed and the caller should retry with a new idempotency key. headers: Retry-After: description: >- Seconds to wait before retrying when the original attempt is still in progress. schema: type: integer content: application/json: schema: $ref: '#/components/schemas/MpcErrorResponse' '422': description: Idempotency key reused with a different signing share pair content: application/json: schema: $ref: '#/components/schemas/MpcErrorResponse' '500': description: Internal server error content: application/json: schema: $ref: '#/components/schemas/MpcErrorResponse' components: parameters: Curve: name: curve in: path required: true description: The elliptic curve to use. schema: type: string enum: - SECP256K1 - ED25519 IdempotencyKey: name: Idempotency-Key in: header required: false description: | A caller-provided key used for safe retries. Behavior depends on the endpoint: - **`POST /v1/presign/{curve}` with `managed: true`** — retrying a completed request with the same key returns the same `{id, expiresAt}` (200). If the original attempt is still in progress, the retry returns 409 with a `Retry-After` header; if the original attempt failed before completing, it returns 409 without `Retry-After` (caller should retry with a new key). Reusing a key after the wallet's signing share has changed (for example, after a reshare or recovery) returns 422. - **`POST /v1/sign`** — only honored for broadcast methods (for example `eth_sendTransaction`, `sol_signAndSendTransaction`). Supplying the header with a non-broadcast method returns 400. For broadcast methods, retrying a completed request returns 409 (`IDEMPOTENT_REQUEST_ALREADY_COMPLETED`), and reuse with a different payload returns 422. On 409, the response body does not include the original signing result — the header prevents double-execution, it does not replay the prior response. - **`POST /v1/assets/send`** — retrying a completed request returns 409 (`IDEMPOTENT_REQUEST_ALREADY_COMPLETED`), and reuse with a different payload returns 422. On 409, the response body does not include the original `transactionHash` — the header prevents double-submission, it does not replay the prior response. Client-stored presignature creation does not currently honor this header. schema: type: string schemas: PresignRequest: type: object description: Request body for creating a presignature. properties: share: type: string description: The JSON-serialized MPC share for the wallet. expirationTs: type: number description: | Unix timestamp for when the presignature expires. Defaults to 7 days from creation. Maximum 365 days. managed: type: boolean default: false description: | Set to `true` to create a Portal-managed presignature, where Portal stores the encrypted payload and returns only an `id`. Defaults to `false`, which creates a client-stored presignature and returns the opaque payload as `data`. required: - share PresignResponse: type: object description: Response containing the created presignature. properties: id: type: string description: Unique identifier for the presignature. expiresAt: type: string format: date-time description: RFC 3339 expiration timestamp. data: type: string description: | Base64-encoded opaque presignature payload for client-stored presignatures. Pass this as the `presignature` field in signing requests. Omitted for Portal-managed presignatures. required: - id - expiresAt MpcErrorResponse: type: object description: Standard error response from the Enclave MPC API. properties: id: type: string description: >- Short error identifier (e.g. `DKG_FAILED`, `BAD_REQUEST`, `RPC_OP_FAILED`). message: type: string description: Human-readable error details. required: - id securitySchemes: bearerAuth: type: http scheme: bearer description: Client API Key or Client Session Token ````