DokuWiki

This is an old revision of the document!

Web Service: ValidateChecksum

The ValidateChecksum web service is used to validate a locally calculated SHA384 checksum against a checksum record that was previously stored in the CeRTNA Portal. The locally calculated checksum_value is obtained by calculating the checksum of a Base64 string contained in a CeRTNA Standard XML PRIA_DOCUMENT node. The checksum_key value contained in RequestChecksumValue (supplied by agent) property or the ResponseChecksumValue (supplied by county) property of the PRIA_DOCUMENT node, provides the index for the checksum_value the caller is validating.

The ValidateChecksum web service, returns true, if the locally calculated value matches the value that was stored for the indexed record, otherwise it returns false.

Request Endpoint

Method	URL
POST	https://apex-prd.certna.org/validatechecksum

Request Body

This endpoint accepts request body parameters using an application/json format.

Request Headers

Key	Value
Content-Type	application/json

JSON Request Parameters

Parm Name	Req/Opt	Format	Description
checksum_key	Required	[string]	The checksum key of a checksum record stored in the CeRTNA Portal.
checksum	Required	[string]	Locally calculated binary checksum value converted to a Base64 string.

JSON Response Parameters

Parm Name	Format	Description
is_valid	[string]	True if checksum values match, otherwise false.
code	[string]	Exception conditions will result in code/message being returned.
message	[string]	Longer description of exception condition.

As noted, any condition that results in an unsuccessful call to the StoreChecksum web service will produce a JSON formatted response with a code and message property populated. Successful calls will result in the checksum_key property being returned. The checksum_key is a required parameter of the ValidateChecksum web service.

Sample Request

Endpoint:

https://apex-prd.certna.org/validatechecksum

Headers:

Content-Type: application/json

Body:

{
  "checksum_key" : "D6D5895C-60BF-4D21-AE5B-945C8E255665",
  "checksum" : "1/l1YnJ1dnWFVbjEcUfp3IkBkPb1XBWhdC34T6nJ3YB859YuAtbhUUEG8Gcwimd1"
}

Sample Response:

Status Code: 200

{
    "is_valid": "true"
}

OR

Status Code: 500 (When an error occurs.)

(example 1)

{
    "Exception": {
        "Code": "DatabaseError",
        "Message": "Conversion failed when converting from a character string to uniqueidentifier."
    }
}

Additional Comments

Comments and sample code are provided for reference purposes only and are not intended to show all exception handling conditions and/or completed code blocks.

Comment 1:

The ValidateChecksum web service requires a Base64 encoded SHA384 checksum to be provided as one of the parameters. Following is a C# / .NET sample code snippet that shows how to generate a SHA3 checksum and convert the hash to a Base64 string:

// The following strBase64DocValue value is retrieved from the DOCUMENT child node of the EMBEDDED_FILE node in the XML document.
 
string strBase64DocValue = " SUkqALLnAAAtVZDKI+R4jhk…";  // Get your Base64 string from the XML doc.
 
string strBase64HashValue = getBase64Hash(strBase64DocValue);  // Use this value in your web service call
 
public static string getBase64Hash(string strB64Source)
{
Encoding u8 = Encoding.UTF8; // We use UTF8 encoding
 
byte[] b64Bytes = u8.GetBytes(strB64Source); // Put the Document B64 string into a byte array
 
byte[] b64HashBytes = SHA384.Create().ComputeHash(b64Bytes);  // Compute the SHA384 hash
 
//Convert the SHA384 hash to a Base64 string
 
string strB64Value = System.Convert.ToBase64String(b64HashBytes, 0, b64HashBytes.Length); 
 
return strB64Value;
}

Comment 2:

Following is a C# / .NET sample code snippet that shows how to call the StoreChecksum web service. Your code will supply the values for the various parameters based on the following:

Parameter	Source
checksum_key	The checksum_key (index) of a checksum record that is stored in the CeRTNA Portal.
checksum	The Base64 encoded value of the SHA384 binary checksum that was calculated for the DOCUMENT string.

Public static void ValidateChecksumExample()
{
// In this example I am picking up the checksum_key and the checksum value I calculated from a 
// form field in the sample application that is available on this Wiki.
 
string strChecksumKey = tbChecksumKey.Text;
string strChecksumValue = tbChecksumValue.Text;
 
// The following value was obtained from your call to the Login web service.
 
string token = "ab34xyz3...";
 
strURL = null;
client = null;
request = null;
response = null;
 
strURL = "https://apex-prd.certna.org/APEX/Service/APEXPublicServer.svc/validatechecksum";
 
client = new RestClient(strURL);
request = new RestRequest(Method.POST);
 
strParms = "{\n\t\"checksum_key\" : \"";
strParms += strChecksumKey;
strParms += "\",\n\t\"checksum\" : \"";
strParms += strChecksumValue;
strParms += "\"\n}";
 
request.AddHeader("Cache-Control", "no-cache");
request.AddHeader("Content-Type", "application/json");
request.AddHeader("access_token", token);
request.AddParameter("ValidateChecksum", strParms, ParameterType.RequestBody);
 
response = client.Execute(request);
 
if (response.IsSuccessful)
{
var jsonResult2 = JsonConvert.DeserializeObject<dynamic>(response.Content);
string strIsValid = jsonResult2.is_valid;
 
// Continue processing based on your true or false result.
}
else
{
var jsonResult2 = JsonConvert.DeserializeObject<dynamic>(response.Content);
string str_ErrorCode = jsonResult2.ToString();
 
// Do something with the error result
}
}

Comment 3:

Please note that before calling the CeRTNA web services you must establish the SecurityProtocol in your ServicePointManager. An example is shown below. The currently recommended protocol is Tls12.

public MainWindow()
{
            InitializeComponent();
            System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls |
                                                  SecurityProtocolType.Tls11 |
                                                  SecurityProtocolType.Tls12 |
                                                  SecurityProtocolType.Ssl3;
}

Comment 4:

CeRTNA has posted a simple Visual Studio 2015 WPF/C# project the CeRTNA Wiki that demonstrates how to look up values in an XML file and how to use the Login, StoreChecksum, and ValidateChecksum web services. The project can be downloaded from the Wiki. As stated earlier, the purpose of the code samples is not to demonstrate well structured code, but rather to provide a very simple, functional sample, that you can use for reference in adding CeRTNA web service calls to your existing application. The code sample is provided as is, however, your production code would be expected to contain more extensive error handling, etc.

Comment 5:

A nice utility for experimenting with web service calls is POSTMAN. You can download a free version of POSTMAN from the following URL: https://www.getpostman.com/apps