Backend

You need to follow some steps so your LiveApp can communicate properly with our Backend.

In addition to the following steps, Ledger also needs to know:

• The base url of the API,
• Any backend authentication information to use the api (token in header…)

Endpoints needed for Sell

In order to communicate with Ledger’s backend, you must provide standardised APIs for Ledger’s Sell aggregator services to call.

There are 5 endpoints needed for the Sell integration:

• To get the list of available fiat, country, payment, method and amount: /capabilities.
• To get the list of available crypto-currencies: /crypto-currencies.
• To get the fiat amount that the user should expect -after all fees are deducted - as a payment for the given crypto amount: /quotes.
• To get the URL of the off-ramp widget to which the user will be redirected. /sell-redirect.
• To create a signed sell binary payload: /sell.

{
  "quoteId": "string",
  "amount": "string",
  "refundAddress": "string",
  "fromCryptoCurrency": "string",
  "toFiatCurrency": "string",
  "payloadCryptoCurrency": "string",
  "nonce": "number"
}

{
  "sellId": "SELL-ID-165940",
  "payinAddress": "0xa0b86991c627e936c1d19d4a2e90a2ce3606eb48",
  "createdAt": "2030-05-26T14:13:39",
  "providerFees": "0.0001",
  "referralFees": "0.0001",
  "payoutNetworkFees": "0.0002",
  "providerSig": {
    "payload": "CgUweGZmZhoFMHhmZmYqBTB4ZmZmOgNCVENCA0JBVEoIMTIwMDAwMDBSCDExNTAwMDAwWhF2ZXJ5IGxvbmd1ZSBub25jZQ==",
    "signature": "MEUCIBRm4PrdgRw0aBwRepuOGGRmR/YPcCoyKNJ7UDjFO030AiEA/VT0anolum0a3X/9lGPeovZHqzeDG9brcUB4zhYmwbs="
  }
}

syntax = "proto3";
package ledger_sell;
 
// (coefficient) * 10^(- exponent)
message UDecimal {
    bytes  coefficient = 1;
    uint32 exponent = 2;
}
 
message NewSellResponse {
    string   trader_email = 1;
    string   in_currency = 2;
    bytes    in_amount = 3;
    string   in_address = 4;
    string   out_currency = 5;
    UDecimal out_amount = 6;
    bytes    device_transaction_id = 7;
}

Ledger IDs mapping

To comply with our integration policies, the LedgerId format must be used (by your /crypto-currencies and /capabilities endpoints) and accepted (by your /quote endpoint and widgetURL) to accurately identify tokens and coins.

You can refer to this API to obtain Ledger IDs. You can use the search parameter to find a specific coin or token. For instance, to search for USDT, you can use this request. The API returns paginated results: to access the next pages, include cursor=<value of the "X-Ledger-Next" header> in your request. Further information is available in the response headers.

Example: let’s say your support AAVE on Ethereum mainnet. The LedgerID for AAVE on Ethereum is ethereum/erc20/aave (as we can see here). This means:

• Your /crypto-currencies endpoint must include ethereum/erc20/aave in its response (along with the other coins/tokens you support), so we know that you support AAVE on Ethereum.
• Your /capabilities endpoint must include ethereum/erc20/aave in its response (along with the other coins/tokens you support).
• Your /quote endpoint must accept ethereum/erc20/aave as a value for the from parameter.
• Your widgetURL must accept ethereum/erc20/aave as a value for the from parameter.

Real-time Status Updates:

To ensure effective communication with Ledger’s backend, you are required to implement a webhook /transaction/{sellId}/status update mechanism. This should notify Ledger real-time whenever there is a change in the status of a transaction. Ledger will provide partners with the necessary webhook URL or address to which the status updates should be sent.

Additionally, if your backend needs to know the transaction status from our system (e.g., whether the transaction was approved or rejected by the user’s device), we provide an optional endpoint /transaction/{sellId}/status

Payload & Signature

Here is a little diagram to explain how the payload and the signature are generated:

• payload: the trade parameters are assembled in a protobuf message. This message is binary encoded to produce a Byte Array. This Byte Array is then base64Url encoded, resulting payload field.
• signature: The payload is signed using ES256 provider’s private key, generating a Byte Array. This Signature Byte Array is then base64Url encoded, producing the Signature field. (more details).

If you need help with the signing process, please refer to our code examples.

Generate Private/Public Key

1. Private Key: Use the following command to generate the private key:

   openssl ecparam -name secp256k1 -genkey -noout -out sample-priv-key-secp256k1.pem

2. Public Key: Derive the public key from the private key using the command:

   openssl ec -in sample-priv-key-secp256k1.pem -pubout > sample-pub-key-secp256k1.pem

Verify Key Information

To inspect the contents of the private key file:

openssl ec -text -in sample-priv-key-secp256k1.pem

Repeat this process for both the production and test environments to generate two distinct key pairs.

Signature usage

• Payload and Signature
  From the provider to Ledger Live. The payload is a protobuf message containing the trade data. It is generated by the provider and sent to Ledger Live.

type Payload struct {
  trader_email,
  in_currency,
  in_amount,
  in_address,
  out_currency,
  out_amount,
  device_transaction_id,
}
R, S := Sign(payload, privKey)

• Validate
  Exchange app checks and validates the payload (signature and content).

// Compare nonce in payload
Verify((R, S), payload, pubKey)

• Display
  Exchange app requests approval to the user by displaying the operation summary on screen.

Validate?
Send currency_from amount_to_provider
Receive currency_to amount_to_wallet

Input field: nonce

A nonce field will be passed as a parameter of the /sell endpoint. It is a 32 bytes nonce which is generated by the hardware wallet to avoid replay attacks.
It will be base 64 URL encoded before being sent to the /sell endpoint.

Output field: providerSig

The real return value of the /sell endpoint is the providerSig field with the JSON Web Signature (JWS) in compact form within:

• providerSig.payload - base64 URL of the binary serialized protobuf message.NewTransactionResponse.
• providerSig.signature - base64 URL of the ES256 signature of providerSig.payload. More details in the JWS signature section.

JWS-Signature

The output field is providerSig, and is based on the flattened JWS JSON, without the optional protected and header parameters.

The algorithms supported by Ledger are ES256 with secp256k1 or secp256r1 curve. There is no need to specify them into the header, as we will store your public key with this information in our system.

As specified in the JWA spec, the signature is a concatenation of the (R, S) pair in a 64 octets array, and not the ASN1 format.

The JWS RFC requires the signature to be computed on: <BASE64URL_HEADER>.<BASE64URL_PAYLOAD>. As we don’t require any header, the signature has to be computed on: .<BASE64URL_PAYLOAD>.