# IAddressValidity

> Assert whether a string represents a valid address.

> For the complete documentation index, see [llms.txt](/llms.txt). Markdown versions of documentation pages are available by appending `.md` to the page URL.

Source: https://dev.flare.network/fdc/reference/IAddressValidity

Assert whether a string represents a valid address on an external blockchain.

Sourced from `IAddressValidity.sol` on [GitHub](https://github.com/flare-foundation/flare-smart-contracts-v2/blob/main/contracts/userInterfaces/fdc/IAddressValidity.sol).

## Overview[​](#overview "Direct link to Overview")

The IAddressValidity interface enables smart contracts to verify if a given string is a valid address on supported external blockchains. This attestation provides standardized representations of addresses across different chains, facilitating cross-chain operations within the Flare ecosystem.

## Supported Chains[​](#supported-chains "Direct link to Supported Chains")

Network Type

Supported Chains

**Mainnet**

`BTC` (Bitcoin), `DOGE` (Dogecoin), `XRP` (XRP Ledger)

**Testnet**

`testBTC` (Bitcoin Testnet 4), `testDOGE`, `testXRP`

## Structs[​](#structs "Direct link to Structs")

### Request[​](#request "Direct link to Request")

Toplevel request structure.

```
struct Request {    bytes32 attestationType;    bytes32 sourceId;    bytes32 messageIntegrityCode;    RequestBody requestBody;}
```

#### Parameters[​](#parameters "Direct link to Parameters")

-   `attestationType`: ID of the attestation type (0x05 for AddressValidity)
-   `sourceId`: ID of the data source (e.g., BTC, DOGE, XRP)
-   `messageIntegrityCode`: MessageIntegrityCode derived from the expected response
-   `requestBody`: Data defining the request

### Response[​](#response "Direct link to Response")

Toplevel response structure.

```
struct Response {    bytes32 attestationType;    bytes32 sourceId;    uint64 votingRound;    uint64 lowestUsedTimestamp;    RequestBody requestBody;    ResponseBody responseBody;}
```

#### Parameters[​](#parameters-1 "Direct link to Parameters")

-   `attestationType`: Extracted from the request
-   `sourceId`: Extracted from the request
-   `votingRound`: The ID of the FDC round in which the request was considered
-   `lowestUsedTimestamp`: The lowest timestamp used to generate the response
-   `requestBody`: Extracted from the request
-   `responseBody`: Data defining the response

### Proof[​](#proof "Direct link to Proof")

Toplevel proof structure for verification.

```
struct Proof {    bytes32[] merkleProof;    Response data;}
```

#### Parameters[​](#parameters-2 "Direct link to Parameters")

-   `merkleProof`: Merkle proof corresponding to the attestation response
-   `data`: Attestation response

### RequestBody[​](#requestbody "Direct link to RequestBody")

Request body specific to address validity.

```
struct RequestBody {    string addressStr;}
```

#### Parameters[​](#parameters-3 "Direct link to Parameters")

-   `addressStr`: Address string to be verified

### ResponseBody[​](#responsebody "Direct link to ResponseBody")

Response body specific to address validity.

```
struct ResponseBody {    bool isValid;    string standardAddress;    bytes32 standardAddressHash;}
```

#### Parameters[​](#parameters-4 "Direct link to Parameters")

-   `isValid`: Boolean indicator of the address validity
-   `standardAddress`: If valid, the standard form of the address; otherwise an empty string
-   `standardAddressHash`: If valid, the standard address hash; otherwise a zero bytes32 string

## Chain-Specific Address Formats[​](#chain-specific-address-formats "Direct link to Chain-Specific Address Formats")

### Bitcoin (BTC)[​](#bitcoin-btc "Direct link to Bitcoin (BTC)")

-   Supports P2PKH, P2SH, P2WPKH, P2WSH, and P2TR addresses
-   Bech32 and Bech32m encoding for SegWit addresses
-   Legacy addresses with Base58Check encoding

### Dogecoin (DOGE)[​](#dogecoin-doge "Direct link to Dogecoin (DOGE)")

-   Supports P2PKH and P2SH addresses
-   Base58Check encoding
-   Different address prefixes than Bitcoin

### XRP Ledger (XRPL)[​](#xrp-ledger-xrpl "Direct link to XRP Ledger (XRPL)")

-   Base58 encoding with checksum
-   Addresses typically start with "r"
-   Supports X-addresses for destination tags

## Implementation Notes[​](#implementation-notes "Direct link to Implementation Notes")

-   The attestation ID for AddressValidity is `0x05`
-   The `lowestUsedTimestamp` value is `0xffffffffffffffff` (maximum 64-bit value)
-   For invalid addresses, `standardAddress` will be empty and `standardAddressHash` will be zero
-   The `standardAddressHash` is computed using `keccak256` on the standardized address string

## Usage Example[​](#usage-example "Direct link to Usage Example")

AddressVerifier.sol

```
// SPDX-License-Identifier: MITpragma solidity ^0.8.25;import {ContractRegistry} from "@flarenetwork/flare-periphery-contracts/coston2/ContractRegistry.sol";import {IFdcVerification} from "@flarenetwork/flare-periphery-contracts/coston2/IFdcVerification.sol";import {IAddressValidity} from "@flarenetwork/flare-periphery-contracts/coston2/IAddressValidity.sol";contract AddressVerifier {    // On-chain business logic: stores the verification status of an address string.    mapping(string => bool) public isAddressVerified;    event AddressVerified(        string indexed addressStr,        string standardAddress,        bytes32 standardAddressHash    );    function processAddressProof(        IAddressValidity.Proof calldata _proof    ) external {        // 1. FDC Logic: Verify the proof's authenticity with the Flare network.        require(isProofValid(_proof), "Invalid address validity proof");        // 2. Business Logic: Execute actions based on the verified proof data.        bool isValid = _proof.data.responseBody.isValid;        string calldata originalAddress = _proof.data.requestBody.addressStr;        // Only take action if the FDC confirms the address is valid.        if (isValid) {            // Take action: update state and emit an event.            isAddressVerified[originalAddress] = true;            emit AddressVerified(                originalAddress,                _proof.data.responseBody.standardAddress,                _proof.data.responseBody.standardAddressHash            );        }    }    function isProofValid(        IAddressValidity.Proof memory _proof    ) public view returns (bool) {        IFdcVerification fdcVerification = ContractRegistry            .getFdcVerification();        return fdcVerification.verifyAddressValidity(_proof);    }}
```

[Open example in Remix](https://remix.ethereum.org/#url=https://github.com/flare-foundation/developer-hub/blob/main/examples/developer-hub-solidity/AddressVerifier.sol&version=builtin&evmVersion=cancun&optimize=true&runs=200)