> ## Documentation Index > Fetch the complete documentation index at: https://developers.circle.com/llms.txt > Use this file to discover all available pages before exploring further. # Create a challenge to sign message > Generates a challenge for signing a message from a specified user-controlled wallet. This endpoint supports Ethereum-based blockchains (using EIP-191), Solana and Aptos (using Ed25519 signatures). Note that Smart Contract Accounts (SCA) are specific to Ethereum and EVM-compatible chains. The difference between Ethereum's EOA and SCA can be found in the [account types guide](https://developers.circle.com/wallets/account-types). You can also check the list of Ethereum Dapps that support SCA: https://eip1271.io/. To identify the wallet, you must provide either `walletId`, or both `walletAddress` and `blockchain` in the request body. ## OpenAPI ````yaml openapi/user-controlled-wallets.yaml post /v1/w3s/user/sign/message openapi: 3.0.3 info: version: '1.0' title: User-Controlled Wallets description: User-Controlled Wallets API documentation. servers: - url: https://api.circle.com security: - BearerAuth: [] tags: - name: Social/ Email Authentication - name: PIN Authentication - name: Users - name: Wallets - name: Transactions - name: Token Lookup - name: Signing paths: /v1/w3s/user/sign/message: post: tags: - Signing summary: Create a challenge to sign message description: > Generates a challenge for signing a message from a specified user-controlled wallet. This endpoint supports Ethereum-based blockchains (using EIP-191), Solana and Aptos (using Ed25519 signatures). Note that Smart Contract Accounts (SCA) are specific to Ethereum and EVM-compatible chains. The difference between Ethereum's EOA and SCA can be found in the [account types guide](https://developers.circle.com/wallets/account-types). You can also check the list of Ethereum Dapps that support SCA: https://eip1271.io/. To identify the wallet, you must provide either `walletId`, or both `walletAddress` and `blockchain` in the request body. operationId: signUserMessage parameters: - $ref: '#/components/parameters/XUserToken' - $ref: '#/components/parameters/XRequestId' requestBody: $ref: '#/components/requestBodies/SignMessage' responses: '200': content: application/json: schema: $ref: '#/components/schemas/Signature' description: Signature already exists headers: X-Request-Id: $ref: '#/components/headers/XRequestId' '201': content: application/json: schema: $ref: '#/components/schemas/Signature' description: Signature created headers: X-Request-Id: $ref: '#/components/headers/XRequestId' '400': $ref: '#/components/responses/BadRequest' '401': $ref: '#/components/responses/NotAuthorized' '404': $ref: '#/components/responses/NotFound' security: - BearerAuth: [] components: parameters: XUserToken: name: X-User-Token description: Unique system generated JWT session token for specific user. required: true in: header schema: type: string XRequestId: name: X-Request-Id in: header description: > Developer-provided identifier for this request, used for tracing requests in Wallets API logs and the Developer Console, and when communicating with Circle Support. **Must be a UUID to appear in logs.** Non-UUID values are accepted by the API but are ignored by logging and tracing systems. schema: $ref: '#/components/schemas/XRequestId' requestBodies: SignMessage: content: application/json: schema: title: SignMessageRequest type: object required: - message properties: walletId: $ref: '#/components/schemas/Id' blockchain: $ref: '#/components/schemas/Blockchain' walletAddress: $ref: '#/components/schemas/Address' encodedByHex: $ref: '#/components/schemas/EncodedByHex' message: $ref: '#/components/schemas/Message' memo: $ref: '#/components/schemas/Memo' required: true description: Sign message for end user request schemas: Signature: title: SignatureResponse type: object required: - data properties: data: type: object required: - challengeId properties: challengeId: $ref: '#/components/schemas/ChallengeId' XRequestId: type: string format: uuid description: >- A unique identifier, which can be helpful for identifying a request when communicating with Circle support. example: 2adba88e-9d63-44bc-b975-9b6ae3440dde Id: type: string format: uuid description: System-generated unique identifier of the resource. example: c4d1da72-111e-4d52-bdbf-2e74a2d803d5 Blockchain: type: string description: >- The blockchain network that the resource is to be created on or is currently on. enum: - ETH - ETH-SEPOLIA - AVAX - AVAX-FUJI - MATIC - MATIC-AMOY - SOL - SOL-DEVNET - ARB - ARB-SEPOLIA - NEAR - NEAR-TESTNET - EVM - EVM-TESTNET - UNI - UNI-SEPOLIA - BASE - BASE-SEPOLIA - OP - OP-SEPOLIA - APTOS - APTOS-TESTNET - ARC-TESTNET - MONAD - MONAD-TESTNET example: MATIC-AMOY Address: title: Address description: > Blockchain generated unique identifier, associated with wallet (account), smart contract or other blockchain objects. type: string example: '0xca9142d0b9804ef5e239d3bc1c7aa0d1c74e7350' EncodedByHex: type: boolean description: >- Indicator of whether the input message is encoded by hex. If TRUE, then the message should be a hex string. By default, it is False. example: false Message: type: string description: >- The user friendly message that needs to be signed. If it is a hex string, encodedByHex needs to be TRUE. The hex string should start with “0x” and have even length. example: I agree with this transfer Memo: type: string description: >- The human readable explanation for this sign action. Useful for presenting with extra information. example: Transfer USDC to Sam ChallengeId: type: string format: uuid description: >- Unique system generated identifier used to initiate a user challenge flow. example: c4d1da72-111e-4d52-bdbf-2e74a2d803d5 headers: XRequestId: description: > Developer-provided header parameter or Circle-generated universally unique identifier (UUID v4). Useful for identifying a specific request when communicating with Circle Support. schema: $ref: '#/components/schemas/XRequestId' responses: BadRequest: content: application/json: schema: type: object title: BadRequestResponse required: - code - message properties: code: type: integer description: Code that corresponds to the error. message: type: string description: Message that describes the error. example: code: 400 message: Bad request. description: Request cannot be processed due to a client error. headers: X-Request-Id: $ref: '#/components/headers/XRequestId' NotAuthorized: content: application/json: schema: type: object title: NotAuthorizedResponse required: - code - message properties: code: type: integer description: Code that corresponds to the error. message: type: string description: Message that describes the error. example: code: 401 message: Malformed authorization. description: >- Request has not been applied because it lacks valid authentication credentials. headers: X-Request-Id: $ref: '#/components/headers/XRequestId' NotFound: content: application/json: schema: type: object title: NotFoundResponse required: - code - message properties: code: type: integer description: Code that corresponds to the error. message: type: string description: Message that describes the error. example: code: 404 message: Not found. description: Specified resource was not found. headers: X-Request-Id: $ref: '#/components/headers/XRequestId' securitySchemes: BearerAuth: type: http scheme: bearer bearerFormat: PREFIX:ID:SECRET description: >- Circle's API Keys are formatted in the following structure "PREFIX:ID:SECRET". All three parts are required to make a successful request. ````