Introduction To PowerShell

What is PowerShell:
- Used for task automation and management
- A framework by Microsoft.
- It is supported by .NET Framework. (As you can see below, you can play around with .Net functionality)

PowerShell has:
- Command-line shell, which is similar to cmd in Windows or terminal in Linux.
- Associated scripting language.


How to install:
You can follow the guide at Installing PowerShell Windows.
If you have installed Microsoft Visual Studio, it also have options to install PowerShell.

How to Start with command-line shell after installation:
- You can follow this guide at Starting the 32-bit Version of PowerShell
Normally in Windows, you also can click "Start" and search for PowerShell.

After starting, the screen is as below. You can type: get-command to see all commands.

PowerShell command-line

Getting Started With PowerShell Command-line

You can play around with PowerShell. In the Command-line Shell, 

Below is one way that you can save a password with SecureString to a text file. Although this is not the good way in terms of security, but this is a good start with PowerShell.

Try the following commands !

Command 1:

$key = (3,4,2,3,56,34,254,222,1,1,2,23,42,54,33,233,1,34,2,7,6,5,35,43)

Command 2:

$pw = read-host "Enter Password" –AsSecureString

Command 3:

ConvertFrom-SecureString $pw -key $key | out-file "path\to\password\file\here\textfile.txt"

Now you have a textfile.txt, and its content might look like this:

76492d1116743f0423413b16050a5345MgB8ADMAVQBBAG8AeQAwAC8AdwBaAFgAZgBxAHMAMgBOAHYAUgBhAG8AaQB3AGcAPQA9AHwAMgAwAGIAMQAyADQANwA0ADUAMQBlADAANQA4ADcANwA0AGMAYwA1ADEANwA2AGMAYQAyAGYAMgBhADQAOAA0ADcANAA2ADYAYgBiADAAYwA3AGIAZABlADIAMgAwADgAYQBlADYANAA1ADUAYwBmADMAMwA2ADMAMwA4ADcAMQA=

In order to decrypt the content, try the following command from the command-line Shell:

Command 4:

$password = cat  "path\to\password\file\here\textfile.txt" | convertto-securestring -key $key

Command 5:

$Ptr = [System.Runtime.InteropServices.Marshal]::SecureStringToCoTaskMemUnicode($password)

command 6:

$result = [System.Runtime.InteropServices.Marshal]::PtrToStringUni($Ptr)

Command 7:

[System.Runtime.InteropServices.Marshal]::ZeroFreeCoTaskMemUnicode($Ptr)

Command 8:

$result

Here it is, $result is the "password" you entered in command 1. 

Just play around with it and you will get more experienced!

UPDATE 1:

Links

Saving Passwords (and preventing other processes from decrypting them)

Windows Data Protection

How To Use: Data Protection

How to Encrypt and Decrypt Data Using DPAPI

Executing PowerShell Scripts from C#

It is a little bit off the scope. Below is the C# code to convert the text of a SecureString stored in a text file to an in-memory SecureString.

public static SecureString ConvertToSecureString(string psProtectedString, byte[] key)

        {

            // '|' is indeed the separater

            byte[] asBytes = Convert.FromBase64String(psProtectedString);

            string[] strArray = Encoding.Unicode.GetString(asBytes).Split(new[] { '|' });

            if (strArray.Length != 3) throw new InvalidDataException("input had incorrect format");

            // strArray[0] is a static/magic header or signature (different passwords produce

            //    the same header)  It unused in our case, looks like 16 bytes as hex-string

            // you know strArray[1] is a base64 string by the '=' at the end

            //    the IV is shorter than the body, and you can verify that it is the IV, 

            //    because it is exactly 16bytes=128bits and it decrypts the password correctly

            // you know strArray[2] is a hex-string because it is [0-9a-f]

            byte[] magicHeader = HexStringToByteArray(psProtectedString.Substring(0, 32));

            byte[] rgbIV = Convert.FromBase64String(strArray[1]);

            byte[] cipherBytes = HexStringToByteArray(strArray[2]);

            // setup the decrypter

            SecureString str = new SecureString();

            SymmetricAlgorithm algorithm = SymmetricAlgorithm.Create();

            ICryptoTransform transform = algorithm.CreateDecryptor(key, rgbIV);

            using (var stream = new CryptoStream(new MemoryStream(cipherBytes), transform, CryptoStreamMode.Read))

            {

                // using this silly loop format to loop one char at a time

                // so we never store the entire password naked in memory

                int numRed = 0;

                byte[] buffer = new byte[2]; // two bytes per unicode char

                while ((numRed = stream.Read(buffer, 0, buffer.Length)) > 0)

                {

                    str.AppendChar(Encoding.Unicode.GetString(buffer).ToCharArray()[0]);

                }

            }

            //

            // non-production code

            // recover the SecureString; just to check

            // from http://stackoverflow.com/questions/818704/how-to-convert-securestring-to-system-string

            //

            IntPtr valuePtr = IntPtr.Zero;

            string secureStringValue = "";

            try

            {

                // get the string back

                valuePtr = Marshal.SecureStringToGlobalAllocUnicode(str);

                secureStringValue = Marshal.PtrToStringUni(valuePtr);

            }

            finally

            {

                Marshal.ZeroFreeGlobalAllocUnicode(valuePtr);

            }

            return str;

        }

        // from http://stackoverflow.com/questions/311165/how-do-you-convert-byte-array-to-hexadecimal-string-and-vice-versa

       

public static byte[] HexStringToByteArray(String hex)

        {

            int NumberChars = hex.Length;

            byte[] bytes = new byte[NumberChars / 2];

            for (int i = 0; i < NumberChars; i += 2) bytes[i / 2] = Convert.ToByte(hex.Substring(i, 2), 16);

            return bytes;

        }

       

public static SecureString DecryptPassword(string psPasswordFile, byte[] key)

        {

            if (!File.Exists(psPasswordFile)) throw new ArgumentException("file does not exist: " + psPasswordFile);

            string formattedCipherText = File.ReadAllText(psPasswordFile);

            return ConvertToSecureString(formattedCipherText, key);

        }