Hi,

if you have the requierment to encrypt strings in Powershell the .NET Framework offers some classes for this case. This is a symmetric encryption. Receiver and Sender uses the same Password/Key to en- and decrypt the message.

First of all you have to load two Assemblies

[System.reflection.assembly]::LoadWithPartialName("System.Security")|out-null
[System.reflection.assembly]::LoadWithPartialName("System.IO")|out-null

This is the Encrypt function. It requieres 4 Parameters.

function fAESEncrypt()
{
	Param(
		[Parameter(Mandatory=$true)][byte[]]$aBytesToBeEncrypted,
		[Parameter(Mandatory=$true)][byte[]]$aPasswordBytes,
		[Parameter(Mandatory=$true)][ref]$raEncryptedBytes,
		[Parameter(Mandatory=$false)][byte[]]$aCustomSalt
	)		
    [byte[]] $encryptedBytes = @()
    # Salt must have at least 8 Bytes!!
    # Encrypt and decrypt must use the same salt
    # Define your own Salt here
    [byte[]]$aSaltBytes = @(4,7,12,254,123,98,34,12,67,12,122,111) 
	if($aCustomSalt.Count -ge 1)
	{
		$aSaltBytes=$aCustomSalt
	}	
    [System.IO.MemoryStream] $oMemoryStream = new-object System.IO.MemoryStream
    [System.Security.Cryptography.RijndaelManaged] $oAES = new-object System.Security.Cryptography.RijndaelManaged
    $oAES.KeySize = 256;
    $oAES.BlockSize = 128;
    [System.Security.Cryptography.Rfc2898DeriveBytes] $oKey = new-object System.Security.Cryptography.Rfc2898DeriveBytes($aPasswordBytes, $aSaltBytes, 1000);
    $oAES.Key = $oKey.GetBytes($oAES.KeySize / 8);
    $oAES.IV = $oKey.GetBytes($oAES.BlockSize / 8);
    $oAES.Mode = [System.Security.Cryptography.CipherMode]::CBC
    $oCryptoStream = new-object System.Security.Cryptography.CryptoStream($oMemoryStream, $oAES.CreateEncryptor(), [System.Security.Cryptography.CryptoStreamMode]::Write)
	try
	{
		$oCryptoStream.Write($aBytesToBeEncrypted, 0, $aBytesToBeEncrypted.Length);
		$oCryptoStream.Close();
	}
	catch [Exception]
	{
		$raEncryptedBytes.Value=[system.text.encoding]::ASCII.GetBytes("Error occured while encoding string. Salt or Password incorrect?")
		return $false
	}	
    $oEncryptedBytes = $oMemoryStream.ToArray();
    $raEncryptedBytes.Value=$oEncryptedBytes;
	return $true
}

And the decrypt function, also 4 parameters are requiered

function fAESDecrypt()
{
	Param(
		[Parameter(Mandatory=$true)][byte[]]$aBytesToDecrypt,
		[Parameter(Mandatory=$true)][byte[]]$aPasswordBytes,
		[Parameter(Mandatory=$true)][ref]$raDecryptedBytes,
		[Parameter(Mandatory=$false)][byte[]]$aCustomSalt
	)	
    [byte[]]$oDecryptedBytes = @();
	# Salt must have at least 8 Bytes!!
	# Encrypt and decrypt must use the same salt
    [byte[]]$aSaltBytes = @(4,7,12,254,123,98,34,12,67,12,122,111) 
	if($aCustomSalt.Count -ge 1)
	{
		$aSaltBytes=$aCustomSalt
	}
    [System.IO.MemoryStream] $oMemoryStream = new-object System.IO.MemoryStream
    [System.Security.Cryptography.RijndaelManaged] $oAES = new-object System.Security.Cryptography.RijndaelManaged
    $oAES.KeySize = 256;
    $oAES.BlockSize = 128;
    [System.Security.Cryptography.Rfc2898DeriveBytes] $oKey = new-object System.Security.Cryptography.Rfc2898DeriveBytes($aPasswordBytes, $aSaltBytes, 1000);
    $oAES.Key = $oKey.GetBytes($oAES.KeySize / 8);
    $oAES.IV = $oKey.GetBytes($oAES.BlockSize / 8);
    $oAES.Mode = [System.Security.Cryptography.CipherMode]::CBC
	$oCryptoStream = new-object System.Security.Cryptography.CryptoStream($oMemoryStream, $oAES.CreateDecryptor(), [System.Security.Cryptography.CryptoStreamMode]::Write)
	try
	{
		$oCryptoStream.Write($aBytesToDecrypt, 0, $aBytesToDecrypt.Length)
		$oCryptoStream.Close()
	}
	catch [Exception]
	{
		$raDecryptedBytes.Value=[system.text.encoding]::ASCII.GetBytes("Error occured while decoding string. Salt or Password incorrect?")
		return $false
	}
    $oDecryptedBytes = $oMemoryStream.ToArray();
	$raDecryptedBytes.Value=$oDecryptedBytes
	return $true
}

And how to use it 🙂 . Define a salt and password for encryption and encrypt the string

$aCustomSalt=@(1,2,3,4,5,6,7,9,10,11,254,253,252)
$sPassword="A Secret Password"
$sInput="A secret Message" 
[byte[]]$aEncryptedMessage=$null
fAESEncrypt ([system.text.encoding]::ASCII.GetBytes($sInput)) ([system.text.encoding]::ASCII.GetBytes($sPassword)) ([ref]$aEncryptedMessage) $aCustomSalt

Decryption

$aCustomSalt=@(1,2,3,4,5,6,7,9,10,11,254,253,252)
$sPassword="A Secret Password"
[byte[]]$aDecryptedMessage=$null
fAESDecrypt $aEncryptedMessage ([system.text.encoding]::ASCII.GetBytes($sPassword)) ([ref]$aDecryptedMessage) $aCustomSalt
write-host "Your Message:" ([System.Text.Encoding]::UTF8.GetString($aDecryptedMessage))

This is it 🙂

Michael