Signature Verification

In addition to the header,webhook-hash when calling back, there's another header with the name,dusupay-signature and this is to help merchants trust that the callbacks originate from the DusuPay servers. Signature verification can be done with the following procedure;
1.Retrieve the value of the dusupay-signature header.
2.Form the string payload to be used in signature verification. This is obtained by concatenating values of the callback data in the format that follows
id:internal_reference:transaction_status:callback_url
where callback_url is the full URL as added to your merchant account settings.
The other values are obtained from the callback data. e.g. assume the following is the callback data 
{
 "id": 226,
 "request_amount": 10,
 "request_currency": "USD",
 "account_amount": 737.9934,
 "account_currency": "UGX",
 "transaction_fee": 21.4018,
 "total_credit": 716.5916,
 "customer_charged": false,
 "provider_id": "mtn_ug",
 "merchant_reference": "76859aae-f148-48c5-9901-2e474cf19b71",
 "internal_reference": "DUSUPAY405GZM1G5JXGA71IK",
 "transaction_status": "COMPLETED",
 "transaction_type": "collection",
 "message": "Transaction Completed Successfully"
}
and that the callback URL is
https://www.sample-url.com/callback
The string payload would therefore be
226:DUSUPAY405GZM1G5JXGA71IK:COMPLETED:https://www.sample-url.com/callback
3.Obtain the public key as described here and store it as a file.
4.Use the public key to verify the signature as described in the example source codes below;
Signature Verification Code Samples
NodeJS
PHP
const crypto = require('crypto');
const fs = require('fs');
​
function isValidSignature() {
 const strPayload = "226:DUSUPAY405GZM1G5JXGA71IK:COMPLETED:https://www.sample-url.com/callback";
 const signature = "value-of-dusupay-signature";
 const publicKeyFile = "path-to-file/dusupay.public.key.pem";
 const publicKey = fs.readFileSync(publicKeyFile).toString().replace(/\\n/g, '\n');
​
 const verify = crypto.createVerify("SHA512");
 verify.write(strPayload);
 verify.end();
​
 /*true or false*/
 return verify.verify(publicKey, signature, 'base64');
}
<?php
​
public function isValidSignature() {
 $file = "path-to-file/dusupay.public.key.pem";
 $keyContent = file_get_contents($file);
 $publicKey = openssl_get_publickey($keyContent);
 $strPayload = "226:DUSUPAY405GZM1G5JXGA71IK:COMPLETED:https://www.sample-url.com/callback";
 $signature = base64_decode("value-of-dusupay-signature");
​
 /*true or false*/
 return openssl_verify($strPayload, $signature, $publicKey, "sha512") == 1;
}
​
?>
Last modified 2yr ago