Generates a cryptographically strong password

New-StrongPassword

function New-StrongPassword
{
<#
.SYNOPSIS
    Returns a strong password of the specified length

.DESCRIPTION
    Returns a strong password of the specified length
    Uses the RNGCryptoServiceProvider to randomly select each character of the password

.PARAMETER Length
    Length of password to generate

.PARAMETER NoNumbers
    If set password will not contain numbers

.PARAMETER NoSpecial
    If set password will not contain special characters: ~!@#$%^&*()

.PARAMETER AsSecureString
    If set returns a System.Security.SecureString object containing the password

.EXAMPLE
    PS C:\> New-StrongPassword 15
    K*5@vp2RrL07COE

.EXAMPLE
    PS C:\> New-StrongPassword -Length 15 -AsSecureString
    System.Security.SecureString

.EXAMPLE
    PS C:\> New-StrongPassword -Length 15 -NoNumbers
    KMHrXl(cATGSOVp

.EXAMPLE
    PS C:\> New-StrongPassword -Length 15 -NoSpecial
    jSqciEAUdoYyj3R

.EXAMPLE
    PS C:\> New-StrongPassword -Length 15 -NoNumbers -NoSpecial
    MUaTnhIkwUcfcfW
#>
    param(
        [Parameter(Mandatory = $True)]
        [int]$Length,
        [switch]$NoNumbers,
        [switch]$NoSpecial,
        [switch]$AsSecureString
    )
    $Chars =  @([char[]]"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")
    
    if(-not $NoNumbers)
    { $Chars = $Chars + [char[]]"0123456789" }
 
    if(-not $NoSpecial)
    { $Chars = $Chars + [char[]]"~!@#$%^&*()" }
 
    $Crypto = New-Object System.Security.Cryptography.RNGCryptoServiceProvider
    [byte[]] $data = New-Object byte[] 1
 
    $crypto.GetNonZeroBytes($data)
    $data = New-Object byte[] $Length
    $crypto.GetNonZeroBytes($data)

    $string = New-Object System.Text.StringBuilder $Length
    $secString = New-Object System.Security.SecureString
    foreach ($b in $data)
    {
        if($AsSecureString)
        { $secString.AppendChar($Chars[$b % ($Chars.Length)]) }
        else
        { $string.Append($Chars[$b % ($Chars.Length)]) | Out-Null }
    }
    if($AsSecureString)
    { return $secString }
    else
    { return $string.ToString() }
    
}