# RSA Signature Verification

## Download the Public Key File

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

{% embed url="<https://govbill.ams3.cdn.digitaloceanspaces.com/govbill-uat.public.key.pem>" %}
Public key for sandbox webhook signature verification
{% endembed %}

{% embed url="<https://govbill.ams3.cdn.digitaloceanspaces.com/govbill-prod.public.key.pem>" %}
Public key for production webhook signature verification
{% endembed %}

## Next Steps

Below is the sample callback data for this demonstration (sample redirect data is available [here](https://docs.govbill.ug/utility-functions/handling-card-redirects));

```json
{
  "id": 266,
  "merchant_reference": "CSTREF2NZQQW53KJMQPE",
  "internal_reference": "GOVNETJFTKL9BSYQQKVKRU",
  "transaction_type": "COLLECTION",
  "request_currency": "UGX",
  "request_amount": 23000,
  "transaction_currency": "UGX",
  "transaction_amount": 23000,
  "transaction_fee": 690,
  "charge_customer": false,
  "total_credit": 22310,
  "provider_code": "airtel_money_ug",
  "transaction_status": "COMPLETED",
  "status_message": "Transaction Completed Successfully",
  "transaction_account": "256752000001",
  "customer_name": "SANDBOX CUSTOMER",
  "institution_name": "Airtel Money"
}
```

1. Obtain the value of the `rsa-signature` header (if callback) OR the value of the `rsa_signature` query parameter (if redirect).
2. Form the string payload to be used in signature verification. This is obtained by concatenating values of the callback/redirect data in the format; `id:internal_reference:transaction_status:merchant_reference`and these values are obtained from the callback/redirect data. The string payload would therefore be `266:GOVNETJFTKL9BSYQQKVKRU:COMPLETED:CSTREF2NZQQW53KJMQPE`
3. Use the public key obtained above to verify the signature as described in the sample source codes below;&#x20;

{% tabs %}
{% tab title="PHP" %}

```php
<?php

public function isValidSignature() {
    $file = "path-to-file/govnet.public.key.pem";
    $keyContent = file_get_contents($file);
    $publicKey = openssl_get_publickey($keyContent);
    $strPayload = "266:GOVNETJFTKL9BSYQQKVKRU:COMPLETED:CSTREF2NZQQW53KJMQPE";
    $signature = base64_decode("value-of-rsa-signature");

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

?>
```

{% endtab %}

{% tab title="NodeJS" %}

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

function isValidSignature() {
    const strPayload = "266:GOVNETJFTKL9BSYQQKVKRU:COMPLETED:CSTREF2NZQQW53KJMQPE";
    const signature = "value-of-rsa-signature";
    const publicKeyFile = "path-to-file/govnet.public.key.pem";
    const publicKey = fs.readFileSync(publicKeyFile).toString().replace(/\\n/g, '\n');

    const verify = crypto.createVerify("SHA256");
    verify.write(strPayload);
    verify.end();

    /*true or false*/
    return verify.verify(publicKey, signature, 'base64');
}
```

{% endtab %}
{% endtabs %}


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