# Signature algorithm

## Data assumption

When generating the signature (`Signature`) in the API request, you need to provide the key in the account, including `PublicKey` and `PrivateKey`,
The key can be obtained from [Console](https://console.scloudsg.com/uaccount/api_manage).

In this example it is assumed:

```
PublicKey  = 'someone@example.com1296235120854146120'
PrivateKey = '46f09bb9fab4f12dfc160dae12273d5332b5debe'
```

> 💡 You can use the above `PublicKey` and `PrivateKey` to debug your code. When you get a consistent signature result (which means your code is correct), you can change it to your own `PublicKey` and `PrivateKey` ` and other API requests.

In this example, it is assumed that the user request parameter string is as follows:

```json
{
    "Action"     :  "DescribeUHostInstance",
    "Region"     :  "cn-bj2",
    "Limit"      :  10,
    "PublicKey"  :  "someone@example.com1296235120854146120"
}
```

Generate the SHA1 signature of the signed string, which is the value of the request parameter `Signature`.

According to the above algorithm, in this example, the calculated `Signature` is **4201919d267504385deb93af19e0197870fed36b**.

## Construct signature

### 1. Arrange request parameters in ascending order by name

```json
{
    "Action"     :  "DescribeUHostInstance",
    "Limit"      :  10,
    "PublicKey"  :  "someone@example.com1296235120854146120",
    "Region"     :  "cn-bj2"
}
```

### 2. Construct the signed parameter string

The construction rules of the signed string are: signed string = concatenation of all request parameters (no HTTP escaping required). And splice the private key of the API key (`PrivateKey`) at the end of this signature string.

```
ActionDescribeUHostInstanceLimit10PublicKeysomeone@example.com1296235120854146120Regioncn-bj246f09bb9fab4f12dfc160dae12273d5332b5debe
```

Notice:

- For bool types, should be encoded as `true/false`
- For floating point number types, if the fractional part is 0, only the integer part should be retained, such as `42.0` should be retained as `42`
- For floating point types, scientific notation cannot be used

### 3. Calculate signature

Use SHA1 to encode the signed string to generate the final signature.