#Requires -Version 4.0

<#
.SYNOPSIS
    "Decrypts" the obfuscated password hashes used by the mail signature tool
.DESCRIPTION
    "Decrypts" the obfuscated password hashes used found in the configuration
    xml file of the mail signature tool. Created to demonstrate that "security
    through obscurity" is totally useless. Storing symmetrically "obfuscated"
    data thogether with the tool used to obfuscate is a extraordinary stupid
    idea. Compiling senstitve stuff into a assembly, dll file, executable or
    what ever is bad practice and doesn't add any security.
.NOTES
    Author: kurator | lagerhaus128.ch
    Revision 0:
        Initial revision
.EXAMPLE
    Get-MailSignatureToolDecryptedPassword -EncryptedString `
    'uYP3vswNj5n7Tk+JQX0/mWqAMbgOMKViTkVp/xonM9wzCKn8TGXWjYsH8O/yxNdU'
#>

Function Get-MailSignatureToolDecryptedPassword {
    [CmdletBinding()] param(
        [Parameter(ParameterSetName="Strings",Mandatory="true")] `
          [String]$EncryptedString
    )
    Try {
        [System.Security.Cryptography.RijndaelManaged]$RijndaelManaged = `
          New-Object System.Security.Cryptography.RijndaelManaged;
        [System.IO.MemoryStream]$MemoryStream = New-Object `
          System.IO.MemoryStream(
            ,
            [Convert]::FromBase64String($EncryptedString)
        )
        [System.Byte[]]$Buffer = New-Object System.Byte[] 16
        $MemoryStream.Read($Buffer,0,16) | Out-Null
        $RijndaelManaged.IV = $Buffer
        Remove-Variable Buffer
        $RijndaelManaged.Key = `
          (New-Object `
          System.Security.Cryptography.MD5CryptoServiceProvider `
          ).ComputeHash(
            [System.Text.Encoding]::UTF8.GetBytes("cixy")
        )
        [System.Security.Cryptography.CryptoStream]$CryptoStream = `
          New-Object System.Security.Cryptography.CryptoStream(
            [System.IO.Stream]$MemoryStream `
            ,$rijndaelManaged.CreateDecryptor() `
            ,[System.Security.Cryptography.CryptoStreamMode]::Read
        )
        [System.Byte[]]$numArray = New-Object System.Byte[] `
          ([int]$MemoryStream.Length - 16 + 1)
        [System.Text.Encoding]::UTF8.GetString(
            $numArray `
            , 0 `
            , $CryptoStream.Read($numArray, 0, $numArray.Length)
        )
    } Catch {
        Write-Error $_.Exception.Message
    }
}