# Signature Algorithm

## General steps for signature generation:

1. Assume that all data sent or received is a set M, and the parameters that **need to be signed** in the set M are sorted from small to large according to the ASCII code of the parameter name (lexicographic order), using the format of URL key-value pairs (i.e. key1=value1\&key2=value2… ) are spliced into a string stringA.
2. Splice `&appSecret=key` at the end of stringA to get the stringSignTemp string, perform an MD5 operation on stringSignTemp, and then convert all characters in the string to uppercase to get the signature value.

## Important Rules to Note

* Parameter name ASCII codes are sorted from small to large (lexicographic order);
* Parameter names are case-sensitive;
* The transmitted signature parameter does not participate in the signature, and the generated signature is verified against the signature value;
* The interface may add fields, and the added extension fields must be supported when verifying signatures.

## Example(PHP)

For example, the parameters passed are as follows:

```
appId: 12345
chainType: 1
merchantOrderNo: 123123123123
productName：Goods
```

Step 1: Remove the parameters that do **not need to be signed**, follow the key=value format for the parameters that **need to be signed**, and sort them in ASCII dictionary order as follows:

{% code overflow="wrap" %}

```php
$stringA = 'appId=12345&chainType=1&merchantOrderNo=123123123123';
```

{% endcode %}

Step 2: Splice \&appSecret=key to the string in the previous step:

{% code overflow="wrap" %}

```php
$stringSignTemp = $stringA.'&appSecret=Key';
```

{% endcode %}

Step 3: Perform the md5 value operation on the string in the previous step:

{% code overflow="wrap" %}

```php
$signature = md5($stringSignTemp);
```

{% endcode %}

Step 4: Convert the above md5 value to uppercase:

```php
$signature = strtoupper($signature);
```