> ## Documentation Index
> Fetch the complete documentation index at: https://developer.cregis.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Signature

## Signature Algorithm

1. From the request parameters, exclude `sign` and all parameters with null or empty values. Then, **sort the remaining parameters lexicographically**.

*Lexicographical Definition: In English dictionaries, words are arranged in order of the first letter (i.e., in the sequence a, b, c... z). If the first letter is the same, compare the second, third, and subsequent letters. If by the end the two words are of different lengths (e.g., "sigh" and "sight"), place the shorter one first.*

2. After sorting, concatenate the parameters in the format "`key1value1key2value2...`".

3. Prepend the `API Key` to the string obtained from step 2.

4. Convert the string from step 3 into an `md5` hash, in lowercase, to get the `sign`. Include this `sign` in the request parameters.

## Signature Example

**step 1** Assuming the `API Key` is:

```
f502a9ac9ca54327986f29c03b271491
```

The **request parameters excluding the 'sign' field** are:

```json theme={null}
{
  "pid": 1382528827416576,
  "currency": "195@195",
  "address": "TXsmKpEuW7qWnXzJLGP9eDLvWPR2GRn1FS",
  "amount": "1.1",
  "remark": "payout",
  "third_party_id": "c9231e604da54469a735af3f449c880f",
  "callback_url": "http://192.168.2.29:9099/callback",
  "nonce": "hwlkk6",
  "timestamp": 1688004243314
}
```

**step 2**  Sort and combine the `non-empty` key-value pairs in dictionary order:

```
addressTXsmKpEuW7qWnXzJLGP9eDLvWPR2GRn1FSamount1.1callback_urlhttp://192.168.2.29:9099/callbackcurrency195@195noncehwlkk6pid1382528827416576remarkpayoutthird_party_idc9231e604da54469a735af3f449c880ftimestamp1688004243314
```

**step 3**  Concatenate the `API key` to the string from the previous step:

```
f502a9ac9ca54327986f29c03b271491addressTXsmKpEuW7qWnXzJLGP9eDLvWPR2GRn1FSamount1.1callback_urlhttp://192.168.2.29:9099/callbackcurrency195@195noncehwlkk6pid1382528827416576remarkpayoutthird_party_idc9231e604da54469a735af3f449c880ftimestamp1688004243314
```

**step 4**  Calculate the MD5 hash of the resulting string. The computed 'sign' value is:

```
c9bae061ae3f5f8d3bfde817f6966c36
```

**final step** Add the computed 'sign' value to the original request parameters:

```json theme={null}
{
  "pid": 1382528827416576,
  "currency": "195@195",
  "address": "TXsmKpEuW7qWnXzJLGP9eDLvWPR2GRn1FS",
  "amount": "1.1",
  "remark": "payout",
  "third_party_id": "c9231e604da54469a735af3f449c880f",
  "callback_url": "http://192.168.2.29:9099/callback",
  "nonce": "hwlkk6",
  "timestamp": 1688004243314,
  "sign": "d6eef2de79e39f434a38efb910213ba6"
}
```