RSA Signature Verification

This section describes how the RSA signature sent in the callback header can be verified. The signature is generated using an RSA Signing. For verification to succeed, the public key is required.

Download the Public Key File

Download the public key file for the specific environment by clicking the link below and store it somewhere on your server

Production

https://qwaap.ams3.cdn.digitaloceanspaces.com/certs/qwaapprod.public.key.pem

Sandbox

https://qwaap.ams3.cdn.digitaloceanspaces.com/certs/qwaap.public.key.pem

Next Steps

Below is the sample callback data for this demonstration

{
    "id": 2061,
    "request_amount": 10000,
    "request_currency": "UGX",
    "transaction_fee": 1000,
    "total_credit": 9000,
    "invoice_number": "QINVNHNU4FMGMHBKA8YQ",
    "merchant_reference": "1184",
    "payment_status": "PAID",
    "transaction_type": "COLLECTION",
    "status_message": "Invoice payment successful"
}

1. Obtain the value of the rsa-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; id:invoice_number:payment_status:merchant_referenceand these values are obtained from the callback data. The string payload would therefore be 2061:QINVNHNU4FMGMHBKA8YQ:PAID:1184

3. Use the public key obtained above to verify the signature as described in the sample source codes below;

PHP

<?php

public function isValidSignature() {
    $file = "path-to-file/qwaap.public.key.pem";
    $keyContent = file_get_contents($file);
    $publicKey = openssl_get_publickey($keyContent);
    $strPayload = "2061:QINVNHNU4FMGMHBKA8YQ:PAID:1184";
    $signature = base64_decode("value-of-rsa-signature");

    /*true or false*/
    return openssl_verify($strPayload, $signature, $publicKey, "sha512") == 1;
}

?>

NodeJS

const crypto = require('crypto');
const fs = require('fs');

function isValidSignature() {
    const strPayload = "2061:QINVNHNU4FMGMHBKA8YQ:PAID:1184";
    const signature = "value-of-rsa-signature";
    const publicKeyFile = "path-to-file/qwaap.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');
}

A valid signature for the above sample callback is shared below. You can copy and use it to test your signature verification workflow.

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