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On this page, we are going to have a look at the implementation for Injective when your users are using a Ledger device through the Keplr wallet. As explained before, Injective uses a different derivation curve from the rest of the Cosmos chains which means that the users have to use the Ethereum app (for now) to interact with Injective. The easiest way all of the edge cases covered and a full out-of-the-box solution for all of the supported wallets on Injective I suggest you have a look at the MsgBroadcaster + WalletStrategy abstraction. If you want to do your own implementation, let’s go through the code example together.

​
Overview

Keplr exposes a experimentalSignEIP712CosmosTx_v0 method which can be utilized to sign EIP712 typed data (automatically generated on the Keplr side by passing a Cosmos StdSignDoc to the method above) and allow EVM-compatible chains to get proper signatures when we have Ledger devices connected through Keplr. Here is the function’s signature: 
/**
 * Sign the sign doc with ethermint's EIP-712 format.
 * The difference from signEthereum(..., EthSignType.EIP712) is that this api returns a new sign doc changed by the user's fee setting and the signature for that sign doc.
 * Encoding tx to EIP-712 format should be done on the side using this api.
 * Not compatible with cosmjs.
 * The returned signature is (r | s | v) format which used in ethereum.
 * v should be 27 or 28 which is used in the ethereum mainnet regardless of chain.
 * @param chainId
 * @param signer
 * @param eip712
 * @param signDoc
 * @param signOptions
 */
experimentalSignEIP712CosmosTx_v0(chainId: string, signer: string, eip712: {
    types: Record<string, {
        name: string;
        type: string;
    }[] | undefined>;
    domain: Record<string, any>;
    primaryType: string;
}, signDoc: StdSignDoc, signOptions?: KeplrSignOptions): Promise<AminoSignResponse>;
What we need to do now is generate the eip712 and the signDoc, pass them to this function and Keplr will ask the user to sign the transaction using the Ethereum app on their Ledger device.

​
Example Implementation

Based on the overview above, let’s now showcase a full example of how to implement signing transactions on Injective using Ledger + Keplr. Keep in mind that the example below takes into consideration that you are using the Msgs interface exported from the @injectivelabs/sdk-ts package. 
import { 
 ChainRestAuthApi,
 BaseAccount,
 createTransaction,
 createWeb3Extension,
 SIGN_AMINO,
 TxGrpcApi,
 createTxRawEIP712,
 ChainRestTendermintApi,
 getGasPriceBasedOnMessage,
 getEip712TypedData
} from '@injectivelabs/sdk-ts'
import { getNetworkEndpoints, NetworkEndpoints, Network } from '@injectivelabs/networks'
import { GeneralException, TransactionException } from '@injectivelabs/exceptions'
import { BigNumberInBase, getStdFee } from '@injectivelabs/utils'

export interface Options {
  ethereumChainId: number /* 1 for Injective mainnet, 5 for Injective testnet */
  chainId: string; /* Injective chain id */
  endpoints: NetworkEndpoints /* can be fetched from @injectivelabs/networks based on the Network */
}

export interface Transaction {
  memo?: string
  injectiveAddress?: string
  msgs: Msgs | Msgs[]

  // In case we manually want to set gas options
  gas?: {
    gasPrice?: string
    gas?: number /** gas limit */
    feePayer?: string
    granter?: string
  }
}

/** Converting EIP712 tx details to Cosmos Std Sign Doc */
export const createEip712StdSignDoc = ({
  memo,
  chainId,
  accountNumber,
  timeoutHeight,
  sequence,
  gas,
  msgs,
}: {
  memo?: string
  chainId: ChainId
  timeoutHeight?: string
  accountNumber: number
  sequence: number
  gas?: string
  msgs: Msgs[]
}) => ({
  chain_id: chainId,
  timeout_height: timeoutHeight || '',
  account_number: accountNumber.toString(),
  sequence: sequence.toString(),
  fee: getStdFee({ gas }),
  msgs: msgs.map((m) => m.toEip712()),
  memo: memo || '',
})

```

/**
 * We use this method only when we want to broadcast a transaction using Ledger on Keplr for Injective
 *
 * Note: Gas estimation not available
 * @param tx the transaction that needs to be broadcasted
 */
export const experimentalBroadcastKeplrWithLedger = async (
  tx: Transaction,
  options: Options
) => {
  const { endpoints, chainId, ethereumChainId } = options
  const msgs = Array.isArray(tx.msgs) ? tx.msgs : [tx.msgs]
  const DEFAULT_BLOCK_TIMEOUT_HEIGHT = 60
  
  /**
   * You choose to perform a check if 
   * the user is indeed connected with Ledger + Keplr
   */
  if (/* your condition here */) {
    throw new GeneralException(
        new Error(
          'This method can only be used when Keplr is connected with Ledger',
        ),
      )
  }

  /** Account Details * */
  const chainRestAuthApi = new ChainRestAuthApi(endpoints.rest)
  const accountDetailsResponse = await chainRestAuthApi.fetchAccount(
    tx.injectiveAddress,
  )
  const baseAccount = BaseAccount.fromRestApi(accountDetailsResponse)
  const accountDetails = baseAccount.toAccountDetails()

  /** Block Details */
  const chainRestTendermintApi = new ChainRestTendermintApi(endpoints.rest)
  const latestBlock = await chainRestTendermintApi.fetchLatestBlock()
  const latestHeight = latestBlock.header.height
  const timeoutHeight = new BigNumberInBase(latestHeight).plus(
    DEFAULT_BLOCK_TIMEOUT_HEIGHT,
  )

  const key = await window.keplr.getKey(chainId)
  const pubKey = Buffer.from(key.pubKey).toString('base64')
  const gas = (tx.gas?.gas || getGasPriceBasedOnMessage(msgs)).toString()

  /** EIP712 for signing on Ethereum wallets */
  const eip712TypedData = getEip712TypedData({
    msgs,
    fee: getStdFee({ ...tx.gas, gas }),
    tx: {
      memo: tx.memo,
      accountNumber: accountDetails.accountNumber.toString(),
      sequence: accountDetails.sequence.toString(),
      timeoutHeight: timeoutHeight.toFixed(),
      chainId,
    },
    ethereumChainId,
  })

  const aminoSignResponse = await window.keplr.experimentalSignEIP712CosmosTx_v0(
    chainId, 
    tx.injectiveAddress,
    eip712TypedData,
    createEip712StdSignDoc({
      ...tx,
      ...baseAccount,
      msgs,
      chainId,
      gas: gas || tx.gas?.gas?.toString(),
      timeoutHeight: timeoutHeight.toFixed(),
    }
  )

  /**
   * Create TxRaw from the signed tx that we
   * get as a response in case the user changed the fee/memo
   * on the Keplr popup
   */
  const { txRaw } = createTransaction({
    pubKey,
    message: msgs,
    memo: aminoSignResponse.signed.memo,
    signMode: SIGN_AMINO,
    fee: aminoSignResponse.signed.fee,
    sequence: parseInt(aminoSignResponse.signed.sequence, 10),
    timeoutHeight: parseInt(
      (aminoSignResponse.signed as any).timeout_height,
      10,
    ),
    accountNumber: parseInt(aminoSignResponse.signed.account_number, 10),
    chainId,
  })

  /** Preparing the transaction for client broadcasting */
  const web3Extension = createWeb3Extension({
    ethereumChainId,
  })
  const txRawEip712 = createTxRawEIP712(txRaw, web3Extension)

  /** Append Signatures */
  const signatureBuff = Buffer.from(
    aminoSignResponse.signature.signature,
    'base64',
  )
  txRawEip712.signatures = [signatureBuff]

  /** Broadcast the transaction */
  const response = await new TxGrpcApi(endpoints.grpc).broadcast(txRawEip712)

  if (response.code !== 0) {
    throw new TransactionException(new Error(response.rawLog), {
      code: UnspecifiedErrorCode,
      contextCode: response.code,
      contextModule: response.codespace,
    })
  }

  return response
}