I’m new in code develop and I’m studying it by myself (books, tutorials, official help of sites…) since a year VB.NET. A lot of information I read is in C# that I rewrite in VB.NET.
I’ve started four months ago to read and write some code about SHA256, Aes, ECDsa… and there are some things those I understand with time and practice, but there are other things that I can’t understand (or find) until read a lot of information. Well in this case, I think I can understand but I don’t know how write the code or understand how SHA256 works.
I’m following these instructions:

[http://gobittest.appspot.com/Address][1]
 
[https://bitcoin.stackexchange.com/questions/37040/ripemd160sha256publickey-where-am-i-going-wrong][2]
<< I think I have the same problem.

I’ll try to be specific and write all necessary code for other people that it could be for their interest. Thank you for advance for all help, links, information that you can give me to follow the right path. Well, this is my situation:
I’ve created a Public key (x coord and y coord) and a private key by ECDsa with SecP256k1 curve. 
This is the code:

    Private Sub GetKeys()
    Using myECDsa As New System.Security.Cryptography.ECDsaCng(vCurve)
    myECDsa.HashAlgorithm = CngAlgorithm.Sha256
    Dim PrivateKey() As Byte = myECDsa.Key.Export(CngKeyBlobFormat.EccPrivateBlob)
    Dim PublicKey() As Byte = myECDsa.Key.Export(CngKeyBlobFormat.EccPublicBlob)
    
    Console.WriteLine(Convert.ToBase64String(PrivateKey))
    Console.WriteLine(Convert.ToBase64String(PublicKey))
    End Using
    End Sub

*vCurve is a var that contains the string “SecP256k1”

Output maybe this:

    Private Key: RUNEViAAAADvJ2dk9gUnYF2XDIr5dNITLUXnXJRgXD8A3WHeDe6YkBBTJAlNizJCp5rMG0163U2JfNWEnBKEE7AjU2guVar63+jTifUg8/UrjTfoLkoIgdk8VLnTz1HYDxEvR2GtE70=
    Public Key: RUNEUCAAAADvJ2dk9gUnYF2XDIr5dNITLUXnXJRgXD8A3WHeDe6YkBBTJAlNizJCp5rMG0163U2JfNWEnBKEE7AjU2guVar6

I can convert to string and clean data if I write this code into Using

    'Private Key
    Dim StrPrivateKey As String = String.Empty
    For Each bt As Byte In PrivateKey
    StrPrivateKey &= bt.ToString("X2")
    Next
    'Public Key
    Dim StrPublicKey As String = String.Empty
    For Each bt As Byte In PublicKey
    StrPublicKey &= bt.ToString("X2")
    Next
    Dim StrDigits As String = StrPrivateKey.Substring(0, 16)
    'Clean data
    StrPrivateKey = StrPrivateKey.Substring(StrPublicKey.Length)
    StrPublicKey = StrPublicKey.Substring(16)
    Dim StrXCoord As String = StrPublicKey.Substring(0, 64)
    Dim StrYCoord As String = StrPublicKey.Substring(64)

Output is:

    Private Key: 6624B7D42BA98F09B4782B755DEE4A050A3E5F15D1DFB152E5A0571ABD045797
    Public Key: C400BED535B984BADCB6DA96D4167709314085B6E5405C7CE1A3D2CF76FA991DC34F2FAA9533FEFD80E6EAA20ED0BD2D7A30F2696A08570B053159FA7068CE90
    Digits: 4543445620000000
    Xcoord: C400BED535B984BADCB6DA96D4167709314085B6E5405C7CE1A3D2CF76FA991D
    YCoord: C34F2FAA9533FEFD80E6EAA20ED0BD2D7A30F2696A08570B053159FA7068CE90

**First Question:**
I saw that every Private/Public key has a similar number or 8 bytes. In this example is: `4543445620000000`

What is this number? Is it a version of something?

**Second Question:**
I’ve found a little information about how to get a SHA256 of Public Key. If I get the SHA256 of this example, the result is:

    Public Key: 04C400BED535B984BADCB6DA96D4167709314085B6E5405C7CE1A3D2CF76FA991DC34F2FAA9533FEFD80E6EAA20ED0BD2D7A30F2696A08570B053159FA7068CE90
    SHA256: f7beda57bd9e0c9838dd4e1336aaa363c2bfa88eca25407b472a620fcaa1626f

Sha256 is correct if I take Public Key as a string (yes, I write “04” at the start and I know that is not a byte). But I’ve read that Public Key must be in bytes, and this is the part where I lost the way. I have PublicKey() as byte, but I don’t know how work with it to get a SHA256. All sha256 tutorials and help about it, hash a single string or files, and as you can see, I need some information that I don’t know how to search.

Thanks a lot.

'------ Edit to write how I'm using SHA256 code. A lot of info I'm reading to learn is form https://docs.microsoft.com

    Public Function FxSHA256(ByVal textHashed As String) As String
            If textHashed.Length <= 0 Then
                MsgBox("No text to hash.")
                Return 0
                Exit Function
            End If
            Dim hash As String = String.Empty
            Using mySHA256 As SHA256 = SHA256.Create()
                hash = ModuleConvert.GetHASH(mySHA256, textHashed)
            End Using
            myHash256 = hash
            Return hash
        End Function

In other module I have this:

    'HashAlgorythm
    Public Function GetHASH(ByVal hashAlgorithm As HashAlgorithm, ByVal textHashed As String) As String
        Dim data As Byte() = hashAlgorithm.ComputeHash(Encoding.UTF8.GetBytes(textHashed))
        Dim sBuilder As New StringBuilder()
        For i As Integer = 0 To data.Length - 1
            sBuilder.Append(data(i).ToString("x2"))
        Next
        Return sBuilder.ToString()
    End Function


  [1]: http://gobittest.appspot.com/Address
  [2]: https://bitcoin.stackexchange.com/questions/37040/ripemd160sha256publickey-where-am-i-going-wrong