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Random Password Generator

There are many occasions when you need to generate a large number of passwords – for example, when testing online systems. Depending on the software involved, you need to be able to configure the size and content of the passwords; the option to include special symbols (non-alphabetic characters) is especially important.

Microsoft has what they call password complexity requirements:

This security setting determines whether passwords must meet complexity requirements. If this policy is enabled, passwords must meet the following minimum requirements when they are changed or created:
  • Not contain significant portions of the user's account name or full name
  • Be at least six characters in length
  • Contain characters from three of the following four categories:
    • English uppercase characters (A through Z).
    • English lowercase characters (a through z).
    • Base 10 digits (0 through 9).
    • Non-alphabetic characters (for example, !, $, #, %).

The Random Password Generator App

The Random Password Generator allows you to configure the size, number, and content of generated passwords:

screenshot

The user interface has these options:

  • Password length - the number of random characters (lower-case letters and numbers) that will be generated for each password.
  • Number of passwords - the number of passwords that will be generated at one time. Even if you only need one password, it's useful to be able to choose from several alternatives.
  • Hyphens - if you don't want any hyphen separators, set this to zero. To enhance readability, you can choose to add hyphens. In the screenshot above, the hyphens are inserted after every 4th character.
  • Include special symbols - this allows you to include special symbols, which may be selected with the Select Special Symbols dialog (which uses a larger font to enhance viewability of small symbols):

    screenshot

Implementation Details

In GenerateRandomPassword.cpp, you will find two functions: GenerateRandomPassword(), which assembles N random characters and then inserts hyphens, and GenerateRandomPasswordChar(), which returns a valid random character. The valid random characters I chose are the simplest possible: upper- and lower-case letters and numbers (base 10 digits). I excluded upper- and lower-case 'O', zero, lower-case l, and 1, since these characters are hard to distinguish in some fonts. You can optionally specify special symbols.

Here is the function header for GenerateRandomPassword(): 

// GenerateRandomPassword()
//
// Purpose:     Generate a random password with optional hyphens
//
// Parameters:  nLength             - password length in TCHARs; does not
//                                    include hyphens.
//              nHyphen             - hyphen insert point;  hyphens will be
//                                    inserted every nHyphen characters.  A 0
//                                    value will suppress hyphen insertion.
//              bSymbols            - TRUE = use special symbols (the valid 
//                                    special symbols should be included in the
//                                    lpszValidCharacters string).
//              lpszValidCharacters - nul-terminated string that contains all
//                                    of the valid characters, including special
//                                    symbols (if allowed).
//
// Returns:     CString             - password string with embedded hyphens, if
//                                    specified
//
// Notes:       All passwords returned by GenerateRandomPassword() will contain
//              a minimum of one lower-case letter, one upper-case letter, and  
//              one digit.  If bSymbols is TRUE, the password will also contain 
//              at least one special symbol.  It is up to the caller to ensure 
//              that lpszValidCharacters contains at least one of each of the 
//              character categories that will be expected.

Testing Password Strength

Microsoft has a free password checker that you can use to check how strong a password is.

Here is its test of the password abcdefgh:

screenshot

Adding an upper-case letter gives this:

screenshot

And adding a number gives this:

screenshot

A password like Ut95-hj36-eiHa-NQ5q will get the highest score:

screenshot

References

Revision History

Version 1.0 - 2009 April 24

  • Initial release.

Buy latest version

Buy Random Password Generator license – $20.00 (includes full source code)