RSA Signature Verification

The 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.

Obtain the Public Key - Based on environment

Copy the public key for the environment you're working with from here. This document assumes that the public key would be stored somewhere on your server under the name ellypay.public.key.pem

Next Steps

Below is the sample callback data for this demonstration

{
    "event": "transaction.charges",
    "payload": {
        "id": 11832,
        "merchant_reference": "MCTREFNGKLP5VQCQSBH2",
        "internal_reference": "ELPREFA65BGTFR7NGUXM",
        "transaction_type": "COLLECTION",
        "request_currency": "UGX",
        "transaction_amount": 100000,
        "transaction_currency": "UGX",
        "transaction_charge": 4000,
        "transaction_account": "256777000001",
        "charge_customer": false,
        "total_credit": 96000,
        "provider_code": "mtn_momo_ug",
        "request_amount": 100000,
        "institution_name": "MTN Mobile Money Uganda",
        "customer_name": "JOHN DOE",
        "transaction_status": "PENDING",
        "status_message": "Collection initialized successfully. Confirm charges"
    }
}
  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; event:merchant_reference:internal_reference:transaction_type:transaction_status and these values are obtained from the callback data. The string payload in this case would therefore be transaction.charges:MCTREFNGKLP5VQCQSBH2:ELPREFA65BGTFR7NGUXM:COLLECTION:PENDING

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

<?php

public function isValidSignature() {
    $file = "path-to-file/ellypay.public.key.pem";
    $keyContent = file_get_contents($file);
    $publicKey = openssl_get_publickey($keyContent);
    $strPayload = "transaction.charges:MCTREFNGKLP5VQCQSBH2:ELPREFA65BGTFR7NGUXM:COLLECTION:PENDING";
    $signature = base64_decode("value-of-rsa-signature");

    /*true or false*/
    return openssl_verify($strPayload, $signature, $publicKey, "sha256") == 1;
}

?>

Below is an example of a generated RSA signature (rsa-signature) on the sandbox environment. Feel free to verify it using the sample payload above and the public key.

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