How to calculate PublisherID from Publisher?

Question 1

I was very close in my guess of how the PublisherId value is constructed. I heard some whispering...

The value is a Crockford’s Base32 encoding of the first eight bytes of SHA-256 hash of the publisher string in UTF-16 (little endian). I have a good implementation that I validated using the sample values from my question.

Question 2

Or you simply use the Kernel32.dll Method PackageFamilyNameFromId:

private static string GetPackageFamilyName(string name, string publisherId)
{
  string packageFamilyName = null;
  PACKAGE_ID packageId = new PACKAGE_ID
  {
    name = name,
    publisher = publisherId
  };
  uint packageFamilyNameLength = 0;
  //First get the length of the Package Name -> Pass NULL as Output Buffer
  if (PackageFamilyNameFromId(packageId, ref packageFamilyNameLength, null) == 122) //ERROR_INSUFFICIENT_BUFFER
  {
    StringBuilder packageFamilyNameBuilder = new StringBuilder((int)packageFamilyNameLength);
    if (PackageFamilyNameFromId(packageId, ref packageFamilyNameLength, packageFamilyNameBuilder) == 0)
    {
      packageFamilyName = packageFamilyNameBuilder.ToString();
    }
  }
  return packageFamilyName;
}

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode, Pack = 4)]
private class PACKAGE_ID
{
  public uint reserved;
  public uint processorArchitecture;
  public ulong version;
  public string name;
  public string publisher;
  public string resourceId;
  public string publisherId;
}


[DllImport("kernel32.dll", CharSet = CharSet.Unicode, ExactSpelling = true)]
private static extern uint PackageFamilyNameFromId(PACKAGE_ID packageId, ref uint packageFamilyNameLength, StringBuilder packageFamilyName);

public static void TestMethod()
{
  GetPackageFamilyName("MyCompany.TestApp", "CN=YourPublisherId");
}

Question 3

Contacted Tomas last Friday for some help; because I couldn't get it to work. But finally I managed to get it to work. The answer Tomas provided contains all the needed components, however I got a hard time to implement it. Especially the Crockford's Base32.

I've created a PowerShell function for it. Hopefully it can help more people out. Like what Tomas already wrote:

Convert to UTF16LE; in PowerShell this is a convert to Unicode (which automatically creates a UTF16 Little Endian format. (When you ouput the Byte array it will mostly contain the character followed by an '0' byte).
Then compute a SHA256 on the whole byte array and pull the first 8 bytes from it. And put the result into a byte array.
The hard part for me; Crockford's Base32 encoding. Base32 is a 5bit encoding; so we need to read 5 bits at a time. So I converted the whole byte array to a binary string. Padding it with zeros to 65 characters; because it has to be a multiple of 5. Then read 5 bits, convert it to decimal. And lookup the decimal index in de encoding string. Read the character on this index and add it to a string. Repeat with every 5 bits.

Final string should be the PublisherId.

Tomas; thanks for your help.

Function Get-PublisherIdFromPublisher ($Publisher) {
    $EncUTF16LE = [system.Text.Encoding]::Unicode
    $EncSha256 = [System.Security.Cryptography.HashAlgorithm]::Create("SHA256")

    # Convert to UTF16 Little Endian
    $UTF16LE = $EncUTF16LE.GetBytes($Publisher)

    # Calculate SHA256 hash on UTF16LE Byte array. Store first 8 bytes in new Byte Array
    $Bytes = @()
    (($EncSha256.ComputeHasH($UTF16LE))[0..7]) | % { $Bytes += '{0:x2}' -f $_ }

    # Convert Byte Array to Binary string; Adding padding zeros on end to it has 13*5 bytes
    $BytesAsBinaryString = -join $Bytes.ForEach{ [convert]::tostring([convert]::ToByte($_,16),2).padleft(8,'0') }
    $BytesAsBinaryString = $BytesAsBinaryString.PadRight(65,'0')

    # Crockford Base32 encode. Read each 5 bits; convert to decimal. Lookup position in lookup table
    $Coded = $null
    For ($i=0;$i -lt (($BytesAsBinaryString.Length)); $i+=5) {
        $String = "0123456789ABCDEFGHJKMNPQRSTVWXYZ"
        [int]$Int = [convert]::Toint32($BytesAsBinaryString.Substring($i,5),2)
        $Coded += $String.Substring($Int,1)
    }
    Return $Coded.tolower()
}