# Generate signature

### Generate signature

The parameter names are sorted according to the order of the ASCII code, converted into a json string, signed with a private key, and HMAC-SHA256 encryption should be used.

#### Signature generation step description

**First step：**

Let's assume all the data sent or received to be the set M, and sort the parameters of the non-empty parameter values in the set M according to the parameter name ASCII code from small to large (dictionary order), using the format of the URL key-value pair (ie key1=value1\&key2=value2) ...) stitched into a string stringA.

**Pay special attention to the following important rules：**

1. The parameter name ASCII code is sorted from small to large (dictionary order);
2. app\_id, timestamp is a required parameter; timestamp is the last five minutes timestamp, which is invalid for more than 5 minutes;
3. If the value of the parameter is null, it does not participate in the signature;
4. Parameter names are case sensitive;
5. The transmitted sign parameter does not participate in the signature, and the generated signature will be checked based on the sign value.

**The Second step：**

The string is finally stitched to get the stringSignTemp string, and the stringSignTemp is programmed according to HMAC-SHA256, and then all the characters of the obtained string are converted to uppercase, then the signvalue is set.

**Pseudo code example**

Assume that the parameters transmitted are as follows： channelId: mttest timestamp : 1516320000 body : test

```
 First step: The parameters are sorted according to the key=value format and sorted according to the parameter name ASCII dictionary order as follows：
 stringA="app_id=mttest&body=test&timestamp=1516320000";
 The second step: splicing the API key:
 stringSignTemp=stringA+"&secret=my_test_secret" 
 sign=hash_hmac("sha256",stringSignTemp,key).toUpperCase()="6A9AE1657590FD6257D693A078E1C3E4BB6BA4DC30B23E0EE2496E54170DACD6" //Note: HMAC-SHA256 signature method"    
```

**Code example**

```
     @Test
     public void deductBalance() throws IOException {
         JTextField field ;
         String url = "http://localhost:8088/channel/deductBalance";
         TreeMap<String,Object> params = Maps.newTreeMap();
         params.put("orderId","my_order_id");
         params.put("channelId","test91021071617412");
         long timestamp = System.currentTimeMillis();
         params.put("timestamp",timestamp);
         String channelSign = getChannelSign(params, secret);
         params.put("sign",channelSign);
         System.out.println(url);
         System.out.println(JSON.toJSONString(params));
         String result = HttpUtils.sendRequestBody(url, params);
         System.out.println(result);
     }
 ​
     public static String getChannelSign(Map<String, Object> params,String secret) {
         StringBuilder result = new StringBuilder();
         if (params != null) {
             for (Object key : params.keySet()) {
                 Object value = params.get(key);
                 result.append(key).append("=").append(value).append("&");
             }
             String tempString = result + "secret=" + secret;
             try {
                 System.out.println(tempString);
                 String sign = EncryptUtils.sha256_HMAC(tempString, secret).toUpperCase();
                 System.out.println(sign);
                 return sign;
             } catch (Exception e) {
                 e.printStackTrace();
             }
         }
         return null;
     }
```

> The parameters and order in which the code participates in encryption are：`channelId=test91021071617412&orderId=my_test_id&timestamp=1547987604644&secret=my_secret`


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