[RESOLVED] SHA-256 as decimal

[NigeH]

Hi,

I'm trying to write some code to produce a checksum for a barcode. The check sum states "All decimal values of the SHA256 checksum are added", and "The decimal 2 digit modulo 100 of the calculated sum are the two checksum digits. E.g.: Checksum Bytes 90, 165, 234 (hex. 5A,A5,EA) -> 90+165+234=489 -> 489 mod 100 = 89"

I have some code working to create a Hexadecimal number from a string and this produced the same hex sting as the online converters, but I am at a loss of how to get this to a decimal value to then work out the final checksum. Any ideas?

eg hex = 84ee032df238e3026bcd8eadbfcff97861a8fad1ca8cd6c2865d89797ba4eea0

[jmcilhinney]

I believe that this should do the job, although it's untested.

Private Function HexToBytes(hex As String) As Byte()
    If hex.Length Mod 2 <> 0 Then
        'Add a leading 0.
        hex = "0" & hex
    End If
 
    Dim index = 0
    Dim bytes As New List(Of Byte)
 
    Do Until index = hex.Length
        bytes.Add(Convert.ToByte(hex.Substring(index, 2), 16))
    Loop
 
    bytes.Reverse()
 
    Return bytes.ToArray()
End Function

[NigeH]

Thanks.

If I call the function - TextBox3.Text = HexToBytes(TextBox2.Text)

I get an error - Value of type 'Byte()' cannot be converted to 'String'

Is that me doing something wrong placing it in the text box?

[jmcilhinney]

Please put some thought into the problem for yourself. Did you even look at my code to see what it does? If my method returns a Byte array, why would you think that you could assign that result to the Text property of a TextBox? You indicated that you already know what to do with an array of Bytes but you don't know how to get an array of Bytes from a hexadecimal String. I just provided code to do the part that you don't know how to do.

[NigeH]

Fair enough, I for some reason thought the function return a string but I see that isn't the case.

I can send my hex string which is in a text box to the function HexToBytes(textbox2.text) and I see that the array "Bytes" holds the data I need. I can work on getting that as a decimal string.

However, when I run the code to see what happens, it crashes with no error and I can't seem to work out why

[NigeH]

However, when I run the code to see what happens, it crashes with no error and I can't seem to work out why

Seems to be looping in the Do Until loop infinitely. Can see the index is not increasing, so added and increment. Had to change - Do Until index = hex.Length - 1

[jmcilhinney]

Seems to be looping in the Do Until loop infinitely.

Sorry, should have incremented the index in the loop:

Do Until index = hex.Length
    bytes.Add(Convert.ToByte(hex.Substring(index, 2), 16))
    index += 2
Loop

[NigeH]

No worries, that is working now and I have a result in the bytes array.

If I print each element in the byte array, will that give me a decimal? Seems to give me a number out, haven't check if it is what I'm after yet.

[NigeH]

So it seems as if I am slightly out with the decimal conversion. I have a few examples...

HEx - 503fe8718d1e6ac380fa7529bfc01235345f63fa8f6af33af3ba1fe64212f65a

My output - 9024618662303118624358243106143250999552531819219141117250128195106301411132326380
online converter - 36297943518230324053527204388021767669526841412357582462543635623660018136666


Hex - 68e656b251e67e8358bef8483ab0d51c6619f3e7a1a9f0e75838d41ff368f728

My output - 4024710424331212568823124016916123124325102282131765872248190881311262308117886230104
OnLine Converter - 47447509435240178963798524362534432113195114210189468302358324674552893339432

Not sure why. All I am doing is.....

        For Each elem As Byte In bytes
            TextBox3.Text &= elem
        Next

[NigeH]

Scrap all that. I've sorted it

Thanks for the help

[passel]

I assume, and for anyone that might wonder what the solution probably was, is the decimal digits is a bit of a red herring, i.e. you don't need to convert the string to a bunch of decimal digits.

Once you have the byte array, you just add the bytes together (i.e. loop through the array and add them to a Long type for instance), and then just do a Mod 100 on the resulting Long value, and use the result (not converted to hex).

[NigeH]

I assume, and for anyone that might wonder what the solution probably was, is the decimal digits is a bit of a red herring, i.e. you don't need to convert the string to a bunch of decimal digits.

Once you have the byte array, you just add the bytes together (i.e. loop through the array and add them to a Long type for instance), and then just do a Mod 100 on the resulting Long value, and use the result (not converted to hex).

Absolutely that. In fact I added them together in the loop I was pulling the hex string together in, as don't really need the hex string either.