# Scrolls Bitcoin API is here!


Scrolls will sign transactions spending from addresses generated by this API. The flow is as follows:

1. Generate a Scrolls address (or a few).
2. Send BTC and/or Charms to the address(es). They are now locked.
3. To unlock, sign the spending transaction with Scrolls. Only transactions carrying correct spells will be signed.


## `GET /config`

Returns the current configuration of the Scrolls Bitcoin API as JSON.
'''json
{
  "fee_address": {
    "main": "bc1qxxxjm06n50uugxewxe5r5w5tskqwq4gkwrm0al",
    "testnet4": "tb1qrk6da5g0592sx6lmgpchaf5qy2lgn8am7cuf3a"
  },
  "fee_per_input": 64,
  "fee_basis_points": 10,
  "fixed_cost": 895
}
'''

Scrolls will only sign transactions if they have a fee output paid to `fee_address`. The fee is calculated as follows:
`fee = fixed_cost + fee_per_input * number_of_inputs + fee_basis_points / 10000 * total_input_sats`


## `GET /{network}/address/{nonce}`

Returns the address derived for `nonce` (64-bit unsigned integer) on `network` ("main" or "testnet4").
The nonce is used to derive the address deterministically: the same nonce always results in the same address
on the same network.

The returned address is a JSON string value (in double quotes).


## `POST /{network}/sign`

```json
{
  "sign_inputs": [
    {
      "index": 0,
      "nonce": 1234567890
    },
    {
      "index": 1,
      "nonce": 1234567890"
    }
  ],
  "prev_txs": ["020000000001025a...529219c900000000", "0200000001b1d12d...b0645dc000000000"],
  "tx_to_sign": "0200000001b1d12d...b0645dc000000000"
}
```

Signs `tx_to_sign` and returns the signed transaction as a hex-encoded string for `network` ("main" or "testnet4").
The `sign_inputs` array contains the indices of the inputs to sign. The `prev_txs` array contains hex encoded
transactions creating the outputs that `tx_to_sign` spends.

The returned signed transaction is a JSON string value (in double quotes).