19 February, 2017

Random password generator - Scripting

These days everything in shops are handcrafted. It's fashionable to buy handcrafted yogurt, honey, jam...beer... why not have your very own homemade password generator?!

It's actually useful to put into scripts which create user accounts in e.g. Active Directory. You can have the given user phone the support team to reset the password when they want to start using the account - so no one knows the password until then.

You really want long (15 characters long) complex passwords because you never know how long a newly created account will sit around waiting for the user to reset the password of it. You can read many books about it why complex and random passwords are needed.

I tell you the whole code upfront and then explain the bits, like in every Columbo episode, they show you the buildup and the murder and then Columbo solves the puzzle in front of your eyes.... Peter Falk was awesome in that character!

The random password generator itself:
[string]::join("",((48..57) + (65..90) + (97..122) | Get-Random -count 15 | %{[char]$_}))

The bits of the oneliner

Passwords need characters, the easiest way to generate some is from the ASCII table. In Powershell you can generate a list of numbers on the fly when you define an array, these can be the ASCII codes of characters:
  • ASCII codes for all lowercase letters: (97..122)
  • ASCII codes for all uppercase letters: (65..90)
  • ASCII codes for all numbers from 0 to 9: (48..57)
You can see there are gaps in the list of ASCII codes of lowercase, uppercase letters and numbers. To make these 3 arrays of numbers look like one array, just add them up together:
(48..57) + (65..90) + (97..122)

Array of ASCII numbers for random password

Nice, we have a list of ASCII codes for all characters we want to chose from, let's pick random ones, 15 of them:
Get-Random -count 15

Then pipe these through to a foreach loop and convert the numbers to characters:

Taking 15 random numbers of the ASCII arrays and converting to characters

Good, we have a random list of characters in an array, but I need it in one long string so I can use it as a real password. For this purpose, we can use the join function of the [string] type with no delimiter:

There you go, you now have your handcrafted random password generator.

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