4.3 Appendix C: Control Key

The ControlKey variable passed back to the merchant is calculated using the following algorithm.

The message is created as below, with the {x} being replaced by the values for each field:

"MerchantIdentifier={x};MerchantReference={x};CorrelationIdentifier={x};CustomerIdentifier={x};CardNumber={x};Amount={x};TransactionReference={x};ErrorCode={x};ErrorDescription={x};BankReference={x};BankResponseCode={x};BankResponseDescription={x}”

If the MerchantTokenReference is different from the CustomerIdentifier then it must also be included in the ControlKey:

"MerchantIdentifier={x};MerchantReference={x};CorrelationIdentifier={x};CustomerIdentifier={x};MerchantTokenReference={x};CardNumber={x};Amount={x};TransactionReference={x};ErrorCode={x};ErrorDescription={x};BankReference={x};BankResponseCode={x};BankResponseDescription={x}”

The message is then encrypted with the merchant’s encryption key. [Merchant user encryption key saved in the payment gateway and setup by the merchant using the Payserver application -  https://psp.vodacompaymentgateway.co.za/PayserverAdmin/Administration/LogOn ].

Example Encryption method (C#)

private string EncryptTheControlKey(string message, string key)
{
    System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding();
    byte[] keyByte = encoding.GetBytes(key);
    HMACSHA256 hmacsha256 = new HMACSHA256(keyByte);
    byte[] messageBytes = encoding.GetBytes(message);
    byte[] hashmessage = hmacsha256.ComputeHash(messageBytes);
    return ByteToString(hashmessage);
}

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