Writing MD5 Hash to file is littered with extraneous characters - vb.net

Question

Update:
I made some edits to clean up remnants of efforts that weren't helping.
I understood previously that "something" is occurring during the file-write process and that it's something that I personally am not perceiving.
Thanks to Plutonix in the comments, I know that the problem is in how I'm handling this but I don't understand exactly how to do it properly and research isn't turning anything up.
I'm attempting to write a file that must be then prefixed with an md5 checksum of itself
The result should be
[hash of "the brown fox"]the brown fox
In the example file I'm testing on, this is the hash I want to reproduce. Viewing in UTF-8 or in Hex reveals that these are the only characters within
¶ Â趓Naþ¼Wô}¾}
VB.net Debug.print produces exactly this
Hash.tostring: ¶ Â趓Naþ¼Wô}¾}
hash.length: 16
hash.tostring.length: 16
utf8hash.length: 28 -- I think this is part of the problem?
The file writes, as seen in UTF-8 or a Hex Editor
¶ Â趓Naþ¼Wô}¾}
This is one variant of most of my efforts
Dim HashMaker As New MD5CryptoServiceProvider()
Dim HashBytes As Byte() = HashMaker.ComputeHash(Encoding.UTF8.GetBytes(sb.ToString()))
Dim Hash As New StringBuilder()
For hx = 0 To HashBytes.Length - 1
Hash.Append(Chr(HashBytes(hx)))
Next
Dim HashMaker As New MD5CryptoServiceProvider()
Dim HashBytes As Byte() = HashMaker.ComputeHash(Encoding.UTF8.GetBytes(sb.ToString()))
Dim Hash As New StringBuilder()
For hx = 0 To HashBytes.Length - 1
Hash.Append(Chr(HashBytes(hx)))
Next
Debug.Print(Hash.ToString())
Dim fHeader As Byte() = New Byte(7) {}
Array.Copy(b, fHeader, 8)
Dim utf8hash As Byte() = Encoding.UTF8.GetBytes(Hash.ToString())
System.IO.File.WriteAllText(fname & "_long", "")
Dim s As New System.IO.FileStream(fname & "_long", System.IO.FileMode.Append, System.IO.FileAccess.Write, System.IO.FileShare.ReadWrite)
s.Write(b, 0, 8)
s.Write(utf8hash, 0, utf8hash.Length)
s.Write(Encoding.UTF8.GetBytes(sb.ToString()), 0, sb.Length)
s.Close()
I've tried an alternate method
Dim utf8 As String = ""
For hx = 0 To HashBytes.Length - 1
Hash.Append(Chr(HashBytes(hx)))
utf8 &= Chr(HashBytes(hx))
Next
Dim fHeader As Byte() = New Byte(7) {}
Array.Copy(b, fHeader, 8)
Dim utf8hash As Byte() = Encoding.UTF8.GetBytes(Hash.ToString())
Debug.Print("Hash.tostring: " & Hash.ToString())
Debug.Print("hash.length: " & Hash.Length)
Debug.Print("hash.tostring.length: " & Hash.ToString.Length)
Debug.Print("utf8hash.length: " & utf8.Length)
System.IO.File.WriteAllText(fname & "_long", "")
Dim s As New System.IO.FileStream(fname & "_long", System.IO.FileMode.Append, System.IO.FileAccess.Write, System.IO.FileShare.ReadWrite)
s.Write(b, 0, 8)
s.Write(Encoding.UTF8.GetBytes(utf8), 0, 16)
s.Write(Encoding.UTF8.GetBytes(sb.ToString()), 0, sb.Length)
As for a Self-contained example:
Imports System.IO
Imports System.Text
Imports System.Text.RegularExpressions
Imports System.Security.Cryptography
Public Class Form1
Private Function TestWrite()
Dim book As Integer = 5, row As Integer = 5
Dim fname As String = "c:\programtestFile.dat"
Dim sb As New StringBuilder
Dim HashMaker As New MD5CryptoServiceProvider()
Dim HashBytes As Byte() = HashMaker.ComputeHash(Encoding.UTF8.GetBytes("test"))
Dim Hash As New StringBuilder()
For hx = 0 To HashBytes.Length - 1
Hash.Append(Chr(HashBytes(hx)))
Next
Debug.Print(Hash.ToString)
Dim utf8hash As Byte() = Encoding.UTF8.GetBytes(Hash.ToString())
System.IO.File.WriteAllText(fname & "_long", "")
Dim s As New System.IO.FileStream(fname & "_long", System.IO.FileMode.Append, System.IO.FileAccess.Write, System.IO.FileShare.ReadWrite)
's.Write(b, 0, 8)
s.Write(utf8hash, 0, utf8hash.Length)
's.Write(Encoding.UTF8.GetBytes(sb.ToString()), 0, sb.Length)
s.Close()
End Function
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
TestWrite()
End Sub
End Class
The code below prints this this to debug window
kÍF!ÓsÊÞNƒ&'´ö (it is prefixed by a tab, part of the computed hash)
But writes this to the file (as can be seen in a hex editor or setting the Encoding to UTF-8
ÂkÃF!ÓsÊÞNÆ’&'´ö

Answer 1

It turned out what I needed to do is assemble all the Bytes into a single Byte Array like so.
The first 8 bytes are a sort of header. The next 16 are an MD5 checksum of the remaining bytes.
I hope this helps someone.
Dim FileBytes(8 + HashBytes.Length + StringBytes.Length - 1) As Byte
Array.Copy(b, 0, FileBytes, 0, 8)
Array.Copy(HashBytes, 0, FileBytes, 8, 16)
Array.Copy(StringBytes, 0, FileBytes, 24, StringBytes.Length)
System.IO.File.WriteAllBytes(fname, FileBytes)