> For the complete documentation index, see [llms.txt](https://developer.prodege.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://developer.prodege.com/demand/authentication/link-signing.md).

# Link Signing

Each survey link can be signed by Prodege. The signature can then be verified within your system to ensure the signature is legitimate. Please consult with your Prodege representative to enable link signing. The signature scheme will be built based on the following formula where ***StringToSign*** consists of all parameters included in the URL, in alphabetical order, and concatenated by a colon (:). The SecretKey will be provided to you by Prodege.  

Base64( SHA256( UTF-8-Encoding-Of(*SecretKey + “:” + StringToSign*) ) ),

### **Example**

Base URL: 

`https://www.mysurveys.com/survey` 

Parameters: 

`a_variable=12345, b_variable=54321, c_variable=1ab2c3d4e5, d_variable=5e4d3c2b1a` 

Secret Key: 

`abcdef123456` 

In this example, the signature would be calculated as follows:  

`Base64(SHA256(UTF-8-Encoding-Of(abcdef123456:a_variable=12345:b_variable=54321:c_variable=1ab2c3d4e5:d_variable=5e4d3c2b1a)))` 

End Result:  

`https://www.mysurveys.com/survey?a_variable=12345&b_variable=54321&c_variable=1ab2c3d4e5&d_variable=5e4d3c2b1a&signature=4E-yZ3M3AjthWeVFNeAK3LYbXbVMbZKUbpt4Iudf3qw` 

Note: As the result of SHA256 can have characters that cannot be passed un-encoded as a query string parameter, the following character replacements must be made:

| **Character** | **Replacement** |
| ------------- | --------------- |
| +             | -               |
| /             | \_              |
| =             | EMPTY STRING    |