Powershell is great for automation and if one wants to reset passwords or create new users, it can be useful to generate the passwords in the Powershell.

The following contains 3 ways how to generate passwords in Powershell:

1. A simple version using the built-in System.Web.Security.Membership
2. Simple random password generator with predefined character set
3. Password Generator that allows to specify the amount of uppercase, lowercase, numeric and special characters

Simple, built-in Password Generator

function Get-RandomPassword {
    param (
        [Parameter(Mandatory)]
        [int] $length,
        [int] $amountOfNonAlphanumeric = 1
    )
    Add-Type -AssemblyName 'System.Web'
    return [System.Web.Security.Membership]::GeneratePassword($length, $amountOfNonAlphanumeric)
}

Get-RandomPassword 8

Generates passwords such as:

# Get-RandomPassword 8 0
kz^RawKy

# Get-RandomPassword 8 1
/vmt@pO|

# Get-RandomPassword 8 2
6@=(9Dx[

# Get-RandomPassword 8 4
fI@W=p${

# Get-RandomPassword 8 7
@+[#$/+M

# Get-RandomPassword 8 8
!&@^*:}*

Simple Random Password Generator with predefined character set

function Get-RandomPassword {
    param (
        [Parameter(Mandatory)]
        [int] $length
    )

    #$charSet = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789{]+-[*=@:)}$^%;(_!&#?>/|.'.ToCharArray()
    $charSet = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'.ToCharArray()

    $rng = New-Object System.Security.Cryptography.RNGCryptoServiceProvider
    $bytes = New-Object byte[]($length)
 
    $rng.GetBytes($bytes)
 
    $result = New-Object char[]($length)
 
    for ($i = 0 ; $i -lt $length ; $i++) {
        $result[$i] = $charSet[$bytes[$i]%$charSet.Length]
    }
 
    return (-join $result)
}

Get-RandomPassword 8

lets generate a few passwords via:

for($i=0;$i-lt8;$i++) { Get-RandomPassword 8 }

OhVGsUdx
Blg2uK3u
gj9qKDH4
bbsTr25Q
zQ4w2jTK
aMAFMols
26BvUY7E
6GR6fZM5

PassGen – Generate passwords with specific requirements

function Get-RandomPassword {
    param (
        [Parameter(Mandatory)]
        [ValidateRange(4,[int]::MaxValue)]
        [int] $length,
        [int] $upper = 1,
        [int] $lower = 1,
        [int] $numeric = 1,
        [int] $special = 1
    )

    if($upper + $lower + $numeric + $special -gt $length) {
        throw "number of upper/lower/numeric/special char must be lower or equal to length"
    }

    $uCharSet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    $lCharSet = "abcdefghijklmnopqrstuvwxyz"
    $nCharSet = "0123456789"
    $sCharSet = "/*-+,!?=()@;:._"
    $charSet = ""

    if($upper -gt 0) { $charSet += $uCharSet }
    if($lower -gt 0) { $charSet += $lCharSet }
    if($numeric -gt 0) { $charSet += $nCharSet }
    if($special -gt 0) { $charSet += $sCharSet }
    
    $charSet = $charSet.ToCharArray()

    $rng = New-Object System.Security.Cryptography.RNGCryptoServiceProvider
    $bytes = New-Object byte[]($length)
    $rng.GetBytes($bytes)
 
    $result = New-Object char[]($length)
    for ($i = 0 ; $i -lt $length ; $i++) {
        $result[$i] = $charSet[$bytes[$i] % $charSet.Length]
    }
    $password = (-join $result)

    $valid = $true
    if($upper   -gt ($password.ToCharArray() | Where-Object {$_ -cin $uCharSet.ToCharArray() }).Count) { $valid = $false }
    if($lower   -gt ($password.ToCharArray() | Where-Object {$_ -cin $lCharSet.ToCharArray() }).Count) { $valid = $false }
    if($numeric -gt ($password.ToCharArray() | Where-Object {$_ -cin $nCharSet.ToCharArray() }).Count) { $valid = $false }
    if($special -gt ($password.ToCharArray() | Where-Object {$_ -cin $sCharSet.ToCharArray() }).Count) { $valid = $false }
 
    if(!$valid) {
         $password = Get-RandomPassword $length $upper $lower $numeric $special
    }

    return $password
}

Get-RandomPassword 8

Generates passwords such as:

# length 8, 1 upper, 1 lower, 1 number, 1 special
Get-RandomPassword 8
!64mQbcY

# at least 4 upper case characters
Get-RandomPassword 8 4
kEyW8IB/

# length 12, at least 2 upper case, 2 lower case, 1 number
Get-RandomPassword 12 2 2 1
USj;,Y5MKyME

# length 12, at least 5 upper case, 5 numbers
Get-RandomPassword 12 -upper 5 -numeric 5
722HE32WWDy!

# length 8, at least 4 lower case, 4 numbers
Get-RandomPassword 8 0 4 4 0
9ub0v47y

# length 8, 2 upper, 2 lower, 2 number, 2 special
Get-RandomPassword 8 2 2 2 2
0=oeS.F4

# length 20, 1 upper, 1 lower, 1 number, 1 special
Get-RandomPassword 20 1 1 1 1
ma/dS@Z+ghuvCfEv=_5V