PowerShell random password generator.

readme.md

New-Password

A random password generator implementation in PowerShell.

Usage

Example

New-Password -Length 20

A single 20 character long password.

Example

10..20 | New-Password

A set of passwords with lengths from 10 to 20 characters.

Example

@(20) * 20 | New-Password

20 passwords, 20 characters long.

Example

New-Password -CharacterSet 'ABCDEF', '1234567890'

A random password generated from the specified set. The password will contain a miniumum of 1 of each character set.

Example

New-Password -CharacterSetCount 0, 1, 2, 3

A password which contains a minimum of 0 from the first set, 1 from the second, 2 from the third, and 3 from the forth.

Thanks

Thanks to faustonascimento on the PowerShell user group channel for helping rewrite this, making it far better than it was.

New-Password.ps1

function New-Password {
    <#
    .SYNOPSIS
        Generate a random password.
    .DESCRIPTION
        Generate a random password.
    .NOTES
        Change log:
            27/11/2017 - faustonascimento - Swapped Get-Random for System.Random.
                                            Swapped Sort-Object for Fisher-Yates shuffle.
            17/03/2017 - Chris Dent - Created.
    #>

    [CmdletBinding()]
    [OutputType([String])]
    param (
        # The length of the password which should be created.
        [Parameter(ValueFromPipeline)]        
        [ValidateRange(8, 255)]
        [Int32]$Length = 10,

        # The character sets the password may contain. A password will contain at least one of each of the characters.
        [String[]]$CharacterSet = ('abcdefghijklmnopqrstuvwxyz',
                                   'ABCDEFGHIJKLMNOPQRSTUVWXYZ',
                                   '0123456789',
                                   '!$%&^.#;'),

        # The number of characters to select from each character set.
        [Int32[]]$CharacterSetCount = (@(1) * $CharacterSet.Count)
    )

    begin {
        $bytes = [Byte[]]::new(4)
        $rng = [System.Security.Cryptography.RandomNumberGenerator]::Create()
        $rng.GetBytes($bytes)

        $seed = [System.BitConverter]::ToInt32($bytes, 0)
        $rnd = [Random]::new($seed)

        if ($CharacterSet.Count -ne $CharacterSetCount.Count) {
            throw "The number of items in -CharacterSet needs to match the number of items in -CharacterSetCount"
        }

        $allCharacterSets = [String]::Concat($CharacterSet)
    }

    process {
        try {
            $requiredCharLength = 0
            foreach ($i in $CharacterSetCount) {
                $requiredCharLength += $i
            }

            if ($requiredCharLength -gt $Length) {
                throw "The sum of characters specified by CharacterSetCount is higher than the desired password length"
            }

            $password = [Char[]]::new($Length)
            $index = 0
        
            for ($i = 0; $i -lt $CharacterSet.Count; $i++) {
                for ($j = 0; $j -lt $CharacterSetCount[$i]; $j++) {
                    $password[$index++] = $CharacterSet[$i][$rnd.Next($CharacterSet[$i].Length)]
                }
            }

            for ($i = $index; $i -lt $Length; $i++) {
                $password[$index++] = $allCharacterSets[$rnd.Next($allCharacterSets.Length)]
            }

            # Fisher-Yates shuffle
            for ($i = $Length; $i -gt 0; $i--) {
                $n = $i - 1
                $m = $rnd.Next($i)
                $j = $password[$m]
                $password[$m] = $password[$n]
                $password[$n] = $j
            }

            [String]::new($password)
        } catch {
            Write-Error -ErrorRecord $_
        }
    }
}