LRC Calculation algorithm

[Sankalp]

Does anyone know how to calculate Longitudinal Redundancy Check(LRC) in
VB.NET?
I am trying to send Visa-II formatted even parity message to a credit
card processor and am not sure how to calculate the LRC which needs to
be appended to the message.

Any pointers would be most helpful.
Thanks in advance.
Sankalp

 

[Guest]

Does anyone know how to calculate Longitudinal Redundancy Check(LRC) in

VB.NET?

I believe that the lrc byte is just the xor of all the data bytes.

 

[Sankalp]

Here is the code that I am using:
GenerateMessageETX() - This function returns the credit card
data and the ETX chanracter in the string format.
Then I create an HTTPWebRequest to the credit card payment gateway.


Dim message As String = pageData

Dim j As Integer

Dim LRC As Byte = "0"

For j = 0 To message.Length - 1
Dim chr As Char = message.Substring(j, 1)
LRC = LRC Xor Convert.ToByte(chr)
Next

Is this the LRC value or do i need to do something else.

Please guide-have been stuck in this for some time now.

Sankalp

 

[Guest]

Dim message As String = pageData
Dim j As Integer
Dim LRC As Byte = "0"
For j = 0 To message.Length - 1
Dim chr As Char = message.Substring(j, 1)
LRC = LRC Xor Convert.ToByte(chr)
Next

I don't like this:
Dim LRC As Byte = "0"

It probably gives a compiler error. I would code like this:

Dim message As String = pageData
Dim lrc As Integer = 0
For j As Integer = 0 To message.Length - 1
lrc = lrc Xor AscW(message.Chars(j))
Next

At this point, my guess is that you should transmit this string:
message & Chr(lrc)
It is your pageData string with one lrc byte appended.

 

[Sankalp]

Thanks A, tried this but doesnt work. Now I am beginning to doubt the
servers as well. They have given us 2 servers to test with one being
the backup server. But, both the servers are returning different
responses to the same message. I guess i will have to verify this with
the company. Thanks for your help again

Sankalp