PHILOSOPHY

Obviously we need some technological help. We need our computers to help us generate robust password and store them securely. There are many great password managers out there to help us securely store and sync our passwords, including commercial offerings and open-source projects. Many of these managers also offer to generate random passwords for us, usually in the form of a random string of meaningless letters numbers and symbols. These kinds of nonsense passwords are certainly secure, but they are often impractical.

Regardless of how good your chosen password manager is, there will always be times when you need to type in your passwords, and that's when random gibberish passwords become a real pain point. As annoying as it is to have to glance over and back at a small cellphone screen to manually type a gibberish password into a computer, that's nothing compared to the annoyance of trying to communicate such a password to a family member, friend, colleague or customer over the phone.

Surely it would be better to have passwords that are still truly random in the way humans can't be, but are also human-friendly in the way random gibberish never will be? This is the problem this module aims to solve.

Rather than randomly choosing many letters, digits, and symbols from a fairly small alphabet of possible characters, this library chooses a small number of words from a large alphabet of possible words as the basis for passwords. Words are easy to remember, easy to read from a screen, easy to type, and easy to communicate over the telephone.

This module uses words to make up the bulk of the passwords it generates, but it also adds carefully placed symbols and digits to add security without making the passwords difficult to remember, read, type, and speak.

In shot, this module is for people who prefer passwords that look like this:

    !15.play.MAJOR.fresh.FLAT.23!

to passwords that look like this:

    eB8.GJXa@TuM

PASSWORD GENERATION ALGORITHM

It's important to understand the algorithm before trying to create your own custom configurations for this module.

The algorithm is broken in to the following steps:

1.

Pick random words from the dictionary.

2.

Apply transformations to the words.

3.

Create pseudo-words made up for randomly chosen digits and add them as the first and last words.

4.

Insert a copy of the same symbol between each of the words and pseudo-words. This symbol is referred to as the separator character.

5.

Pad the password with multiple instances of the same symbol front and/or back. This symbol is referred to as the padding character.

You can visualise this process as follows:

    correct horse batter staple
    correct HORSE battery staple
    25 correct HORSE battery staple 83
    25*correct*HORSE*battery*staple*83
    ++25*correct*HORSE*battery*staple*83++

Each of these steps can be customised in the following ways:

1.

The number of words to be used, and the minimum and maximum lengths of the words can be configured.

2.

The case of the words can be modified in a number of ways, including randomly choosing the case for each word.

It is also possible to specify so-called 133t-style character substitutions, e.g. replacing all occurrences of the letter "e" with the digit 3, or all occurrences of the letter "s" with the symbol "$".

3.

The number of digits to add as pseudo words to the front and back of the password can be configured. A length of zero can be specified for both to generate passwords without any randomly chosen digits.

4.

The separator character can be specified directly, or it can be randomly chosen from a list of symbols. It is also possible to specify that no separator should be used.

5.

The padding character can also be specified directly, or remotely chosen from a list of possible symbols. Padding can also be disabled completely. If padding is to be used it can be applied in two modes - fixed, and adaptive.

With fixed padding a specified number of copies of the separator character are added to the front and back of the password. The fixed padding does not have to be symmetric.

With adaptive padding the required number of copies of the separator character are added to the back of the password until it reaches a specified length.

THE MATHS

Maths Primer

A coin could be used as a very simple password generator. Each character in the password would be the result of a single coin toss. If the coin lands heads up, we add a "H" to our password, if it lands tails up, we add a "T".

If you made a one-letter password in this way there would only be two possibilities, "H", or "T", or two permutations. If you made a two-letter password in this way there would be four possible combinations, or permutations, "HH", "HT", "TH", and "TT". If you made a three-character password in this way there would be 16 permutations, a five character one would have 32 permutations, and so forth.

So, for a coin toss, which has two possible values for each character, the formula for the number of permutations "P" for a given length of password "L" is:

    P = 2^L

Or, two to the power of the length of the password.

If we now swapped our coin for a dice, we would go from two possible values per letter, to six possible values per letter. For one dice roll there would be six permutations, for two there would be 36, for three there would be 108 and so on.

This means that for a dice, the number of permutations can be calculated with the formula:

    P = 6^L

When talking about passwords, the set of possible symbols used for each character in the password is referred to as the password's alphabet. So, for the coin toss the alphabet was just "H" and "T", and for the dice it was 1, 2, 3, 4, 5, and 6. The actual characters used in the alphabet make no difference to the strength of the password, all that matters is the size of the alphabet, which we'll call "A".

As you can probably infer from the two examples above, the formula for the number of possible permutations "P" for a password of length "L" created from an alphabet of size "A" is:

    P = A^L

In the real world our passwords are generally made up of a mix of letters, digits, and symbols. If we use mixed case that gives us 52 letters alone, then add in the ten digits from 0 to 9 and we're already up to 62 possible characters before we even start on the array of symbols and punctuation characters on our keyboards. It's generally accepted that if you include symbols and punctuation, there are 95 characters available for use in randomly generated passwords. Hence, in the real-world, the value for "A" is assumed to be 95. When you start raising a number as big as 95 to even low powers the number of permutations quickly rises.

A two character password with alphabet of 95 has 9025 permutations, increasing the length to three characters brings that up to 857,375, and so on. These numbers very quickly become too big to handle. For just an 8 character password we are talking about 6,634,204,312,890,625 permutations, which is a number so big most people couldn't say it (what do you call something a thousand times bigger than a trillion?).

Because the numbers get so astronomically big so quickly, computer scientists use bits of entropy to measure password strength rather than the number of permutations. The formula to turn permutations into bits of entropy "E" is very simple:

    E = Log(2)P

In other words, the entropy is the log to base two of the permutations. For our eight character example that equates to about 52 bits.

There are two approaches to increasing the number of permutations, and hence the entropy, you can choose more characters, or, you can make the alphabet you are choosing from bigger.

The Entropy of HSXKPasswd Passwords

Exactly how much entropy does a password need? That's the subject of much debate, and the answer ultimately depends on the value of the assets being protected by the password.

Two common recommendations you hear are 8 characters containing a mix of upper and lower case letters, digits, and symbols, or 12 characters with the same composition. These evaluation to approximately 52 bits of entropy and 78 bits of entropy respectively.

When evaluating the entropy of passwords generated by this module, it has to be done from two points of view for the answer to be meaningful. Firstly, a best-case scenario - the attacker has absolutely no knowledge of how the password was generated, and hence must mount a brute-force attack. Then, secondly from the point of view of an attacker with full knowledge of how the password was generated. Not just the knowledge that this module was used, but a copy of the dictionary file used, and, a copy of the configuration settings used.

For the purpose of this documentation, the entropy in the first scenario, the brute force attack, will be referred to as the blind entropy, and the entropy in the second scenario the seen entropy.

The blind entropy is solely determined by the configuration settings, the seen entropy depends on both the settings and the dictionary file used.

Calculating the bind entropy "Eb" is quite straightforward, we just need to know the size of the alphabet resulting from the configuration "A", and the minimum length of passwords generated with the configuration "L", and plug those values into this formula:

    Eb = Log(2)(A^L)

Calculating "A" simply involves determining whether or not the configuration results in a mix of letter cases (26 or 52 characters), the inclusion of at least one symbol (if any one is present, assume the industry standard of a 33 character search space), and the inclusion of at least one digit (10 character). This will result in a value between 26 and 95.

Calculating "L" is also straightforward. The one minor complication is that some configurations result in a variable length password. In this case, assume the shortest possible length the configuration could produce.

The example password from the "PHILOSOPHY" section ("!15.play.MAJOR.fresh.FLAT.23!") was generated using the preset "WEB32". This preset uses four words of between four and five letters long, with the case of each word randomly set to all lower or all upper as the basis for the password, it then chooses two pairs of random digits as extra words to go front and back, before separating each word with a copy of a randomly chosen symbol, and padding the front and back of the password with a copy of a different randomly chosen symbol. This results in passwords that contain a mix of cases, digits, and symbols, and are between 27 and 31 characters long. If we add these values into the formula we find that the blind entropy for passwords created with this preset is:

    Eb = Log(2)(95^27) = 163 bits

This is spectacularly secure! And, this is the most likely kind of attack for a password to face. However, to have confidence in the password we must also now calculate the entropy when the attacker knows everything about how the password was generated.

We will calculate the entropy resulting from the same "WEB32" config being used to generate a password using the sample library file that ships with the module.

The number of permutations the attacker needs to check is purely the product of possibly results for each random choice made during the assembly of the password.

Lets start with the words that will form the core of the password. The configuration chooses four words of between four and five letters long from the dictionary, and then randomises their case, effectively making it a choice from twice as many words (each word in each case).

The sample dictionary file contains 698 words of the configured length, which doubles to 1396. Choosing four words from that very large alphabet gives a starting point of "1396^4", or 3,797,883,801,856 permutations.

Next we need to calculate the permutations for the separator character. The configuration specifies just nine permitted characters, and we choose just one, so that equates to 9 permutations.

Similarly, the padding character on the end is chosen from 13 permitted symbols giving 13 more permutations.

Finally, there are four randomly chosen digits, giving "10^4", or 10,000 permutations.

The total number of permutations is the product of all these permutations:

    Pseen = 3,797,883,801,856 * 9 * 13 * 10,000 = 2.77x10^17

Finally, we convert this to entropy by taking the base 2 log:

    Eseen = Log(2)2.77x10^17 = ~57bits

What this means is that most probably, passwords generated with this preset using the sample dictionary file are spectacularly more secure than even 12 randomly chosen characters, and, that in the very unlikely event that an attackers knows absolutely everything about how the password was generated, it is still significantly more secure than 8 randomly chosen characters.

Because the exact strength of the passwords produced by this module depend on the configuration and dictionary file used, the constructor does the above math when creating an HSXKPasswd object, and throws a warning if either the blind entropy falls below 78bits, or the seen entropy falls below 52 bits.

MODULE CONFIGURATION

    # get the current debug status
    my $debug_status = Crypt::HSXKPasswd->module_config('DEBUG');
    
    # configure the module to suppress all entropy warnings
    Crypt::HSXKPasswd->module_config('ENTROPY_WARNINGS', 'NONE');

The following module configuration keys exist within the module:

• "DEBUG" - A True/False value denoting whether or not the module should print debug messages. The default is not to print debug messages.

  For more details see the DIAGNOSTICS section of this document.

• "LOG_ERRORS" - A True/False value denoting whether or not errors should be logged. The default is not to log.

  For more details see the DIAGNOSTICS section of this document.

• "LOG_STREAM" - the stream to which debug messages should be printed if debugging is enabled, and log messages should be printed when error logging is enabled. The default is to print to "STDERR".

  For more details see the DIAGNOSTICS section of this document.

• "ENTROPY_MIN_BLIND" - the minimum allowable entropy against brute force attacks in bits. The default is 78 bits.

  For more details see the ENTROPY CHECKING section of this document.

• "ENTROPY_MIN_SEEN" - the minimum allowable entropy against an attacker with full knowledge. The default is 52 bits.

  For more details see the ENTROPY CHECKING section of this document.

• "ENTROPY_WARNINGS" - control the emission of entropy warnings. The value must be one of "ALL", "BLIND", or "NONE". The default value is "ALL".

  For more details see the ENTROPY CHECKING section of this document.

CUSTOM DATA TYPES

Defined Types

• "NonEmptyString" - a string containing at least one character.
• "PositiveInteger" - a whole number greater than or equal to zero.
• "NonZeroPositiveInteger" - a whole number greater than zero.
• "TrueFalse" - a reasonable boolean value, specifically, "undef", and empty string, or 0 to indicate false, and a 1 to indicate true.
• "PerlPackageName" - string representing a valid Perl package name like "Crypt::HSXKPasswd::Dictionary::NL".
• "Letter" - a string containing a single letter. Because this module is Unicode-aware, it should be noted that a letter is defined as a single Unicode grapheme with the Unicode property "Letter". What this means is that accented letters like "é" are considered valid, as are ligatures like "æ".
• "Symbol" - a string containing a single non-letter character. Because this module is Unicode-aware, should be noted that a non-letter character is defined as a single Unicode grapheme that does not have the Unicode property "Letter". What this means is that neither letters, accented characters, nor ligatures can be used as symbols, but just about every other Unicode character can, including punctuation symbols, mathematical symbols, and even emoji!
• "Word" - a string containing only letters (as defined by the type "Letter"), and at least four long.
• "SymbolAlphabet" - a symbol alphabet is a reference to an array that contains at least two distinct symbols (as defined by the type "Symbol"), and no values that are not symbols.
• "WordLength" - a valid value when specifying the length of a word, specifically, a whole number greater than or equal to four.
• "ConfigKeyDefinition" - a valid configuration key definition. A reference to a hash mapping "required" to a true/false value, "expects" to a non-empty string, and "type" to a "Type::Tiny" object.
• "ConfigKeyName" - a valid configuration key name, see the CONFIGURATION section of this document for a description of each configuration key supported by this module. You can get a list of valid configuration key names programatically by calling the function "Crypt::HSXKPasswd-"defined_config_keys()>.
• "ConfigKeyAssignment" - a mapping between a valid configuration key name and a valid value for that configuration key.
• "ConfigOverride" - a reference to hash containing one or more configuration key assignments as defined by the type "ConfigKeyAssignment".
• "Config" - a reference to a hash that contains a complete and valid set of mappings between configuration key names and values. For a config to be considered valid it must contain only valid valid configuration key assignments as defined by the type "ConfigKeyAssignment", must contain a configuration key assignment for each required configuration key and all interdependencies between the specified configuration key assignments must be fulfilled.

  See the CONFIG section of this document for a detailed description of each of the defined configuration keys and their various interdependencies.

• "PresetDefinition" - a valid preset definition. A reference to a hash mapping "description" to a non-empty string, and "config" to a valid Config.
• "PresetName" - a valid preset name, see the PRESETS section of this document for a description of each preset supported by this module. You can get a list of valid preset names programatically by calling the function "Crypt::HSXKPasswd-"defined_presets()>.

Using the Custom Types

The library of custom types is defined in the package "Crypt::HSXKPasswd::Types", and it is a standard "Type::Library" type library containing "Type::Tiny" type definitions.

Useful Links:

• The documentation for "Type::Tiny" - <http://search.cpan.org/perldoc?Type%3A%3ATiny>
• The documentation for "Type::Library" - <http://search.cpan.org/perldoc?Type%3A%3ALibrary>

To use the bare type definitions listed above, import the module as follows:

    use Crypt::HSXKPasswd::Types qw( :types );

Each type listed above will now be imported, and become available as a bare word. The "Type::Tiny" documentation provides a full list of available functions, but the examples below illustrate some of the more useful ones:

    $is_valid = Letter->check('e'); # $is_valid = 1
    $is_valid = Letter->check('-'); # $is_valid = undef
    $err_msg = Letter->validate('e'); # $err_msg = undef
    $err_msg = Letter->validate('-'); # $err_msg = "'-' is not a Letter ...
                    # ... (must be a string containing exactly one letter)"

"Type::Library" automatically creates an "is_TypeName" function for each type defined in the library. These are not imported by default. To import them add the export tag ":is" to the "use" line. I would recommend the following "use" line:

    use Crypt::HSXKPasswd::Types qw( :types :is );

You can now do things like the following:

    $is_valid = is_Letter('e'); # $is_valid = 1
    $is_valid = is_Letter('-'); # $is_valid = undef

Each of the types listed above also contains a custom function using "Type::Tiny"'s new, and still officially experimental, "my_methods" feature. The custom function is called "my_english", and can be used to return an English description of the values considered valid by the type, e.g.:

    print Letter->my_english(); # prints: a string containing exactly one letter

As well as the named types listed above, there are also anonymous types defined for each supported configuration key. These can be accessed using the function "Crypt::HSXKPasswd-"config_key_definitions()>.

If declaring your own "Type::Tiny" types, you may also find the public subroutine "Crypt::HSXKPasswd::Types::var_to_string()" useful - it will turn anything passed as a scalar into a meaningful string, truncating any resulting strings longer than 72 characters in nice way. All the custom error messages in all the types defined in "Crypt::HSXKPasswd::Types" make use of this subroutine.

CONFIGURATION

First, a set of words are randomly chosen from the word source. Then, two pseudo-words made of one or more digits may added before and/or after the words from. Next, a separator character may be placed between all the words (including the groups of digits), and one or more occurrences of a padding symbol may be added front and/or back.

You can envisage the process as follows:

    correct HORSE BATTERY staple
    34 correct HORSE BATTERY staple 56
    34-correct-HORSE-BATTERY-staple-56
    !!34-correct-HORSE-BATTERY-staple-56!!

Many aspects of this password generation process are configurable. You can control the length and number of words chosen, and what, if any, case transformations should be applied to those words, and how accented characters should be treated. How many, if any, digits should be added front and back. What symbol, if any, should be used as a separator. And finally how the password should be padded, if at all, and with what symbol. Passwords can be padded to a given length, or by a given number of symbols front and back.

The symbols used as the separator and for padding can be explicitly specified, or the they can be randomly chosen from a given alphabet of possible symbols. Both symbols can be randomly chosen from the same alphabet, or from two separately specified alphabets.

Every instance of an HSXKPasswd password generator stores its configuration as a set of name-value pairs, referred to as configuration keys throughout this documentation.

Configurations can be specified either as a complete set of configuration keys with values that together form a valid configuration, as a named preset, or, as a named preset accompanied by a list of one or more configuration keys with new values to override those specified by the preset.

The module contains a preset called "DEFAULT", and this preset is used if no configuration is specified. The function "default_config()" will return a copy of this configuration as a reference to a hashtable.

For more details on how to specify configurations, see the documentation for the constructor (the function "new()") below.

Password Generator Configuration Keys

Below is a list of all the configuration keys that can be used to customise the password generation algorithm. Each configuration key is accompanied by a description of what aspect of the algorithm they control, and any validation rules that apply to the key.

Note that some keys are always required, and that there are dependencies between keys. For examples, if you specify that the separator symbol should be chosen at random, you must also specify an alphabet from which the symbol should be randomly chosen.

• "allow_accents" (optional) - if not specified, or if a falsy value is specified, accents will be removed from letters in the generated passwords. E.g. "é" becomes "e". If a truthy value is specified, accents will be preserved, and appear in the generated passwords.
• "case_transform" (required) - the transformations, if any, that should be applied to the words that appear in the generated passwords. The value specified must be one of the following:

• "character_substitutions" (optional) - a reference to a hashtable containing containing zero or more character substitutions to be applied to the randomly chosen words when generating passwords. The keys in the hashtable must be single letters. The substitutions can contain multiple characters. Specifying one or more substitutions with a length greater than one could lead to passwords being longer than expected, and to entropy calculations being under estimated. The module will issue a warning when such a config is loaded.
• "num_words" (required) - the number of words to randomly choose from the word source as the basis for the generated passwords.

  The function "default_config()" returns a value of 3 for this key.

• "pad_to_length" (conditionally required) - the length generated passwords must be padded to when using adaptive padding, i.e. when "padding_type" is set to "ADAPTIVE"). The value must be an integer greater than or equal to 12. Lengths of less than 12 are not permitted for security reasons.
• "padding_alphabet" (optional) - this key is ignored unless the configuration specifies that the padding character should be randomly chosen, i.e. unless "padding_character" is set to "RANDOM".

  When the padding character is set to be randomly chosen, the module will check for the presence of this key. If it is specified, the padding character will be randomly chosen from the set of symbols defined by this key. If this key is not set, the module will use the set of symbols specified by the key "symbol_alphabet". If neither this key nor "symbol_alphabet" are specified, then the configuration will be considered invalid.

  If specified, this key must be a reference to an array of single-character strings.

• "padding_character" (conditionally required) - this key is unless the key "padding_type" is set to "NONE". It specifies the padding symbol to be used when generating passwords.

  If specified, they key's value must be a single character string, or one of the following special values:

• "padding_characters_before" & "padding_characters_after" (conditionally required) - both of these keys are required if the key "padding_type" is set to "FIXED".

  These keys specify the number of padding symbols that should be added to the front and back of the password.

  Both keys require that the specified value be an integer greater than or equal to zero.

  The function "default_config()" returns a value of 2 for both of these keys.

• "padding_digits_before" & "padding_digits_after" (required) - the number of random digits to include before and after the randomly chosen words when generating passwords.

  Both keys require that the specified value be an integer greater than or equal to zero.

  The function "default_config()" returns a value of 2 for both of these keys.

• "padding_type" (required) - the way in which padding symbols should be added when generating passwords.

  Only the following values are valid for this key:

• "separator_alphabet" (optional) - this key is ignored unless the configuration specifies that the separator character should be randomly chosen, i.e. unless "separator_character" is set to "RANDOM".

  When the separator character is set to be randomly chosen, the module will check for the presence of this key. If it is specified, the separator character will be randomly chosen from the set of symbols defined by this key. If this key is not set, the module will use the set of symbols specified by the key "symbol_alphabet". If neither this key nor "symbol_alphabet" are specified, then the configuration will be considered invalid.

  If specified, this key must be a reference to an array of single-character strings.

• "separator_character" (required) - the symbol to use to separate the words when generating passwords.

  The value specified for this key must be a single-character string, or one of the following special values:

• "symbol_alphabet" (optional) - this key specifies a default alphabet of symbols that can be used when either or both the separator character and the padding character are set to be chosen at random. I.e. when either or both of the keys "separator_character" and "padding_character" are set to "RANDOM".

  Note that the keys "separator_alphabet" and "padding_alphabet" take precedence over this key if specified.

  The value specified for this key must be a reference to an array of single-character strings.

  The function "default_config()" returns a value of "['!', '@', '$', '%', '^', '&', '*', '-', '_', '+', '=', ':', '|', '~', '?', '/', '.', ';']" for this key.

• "word_length_min" & "word_length_max" (required) - the minimum and maximum length of the words that will form the basis of the generated passwords.

  The values specified for both keys must be integers greater than three, and the value specified for "word_length_max" must be greater than or equal to the value specified for "word_length_min".

  The function "default_config()" returns values of 4 and 8 for these keys.

PRESETS

This information can be accessed programatically using the functions "defined_presets()", "presets_to_string()", "preset_description()", and "preset_config()".

• "APPLEID" - a preset respecting the many prerequisites Apple places on Apple ID passwords. Apple's official password policy cam be found at the following URL: <http://support.apple.com/kb/ht4232>. Note that Apple's knowledge base article omits to mention that passwords can't be longer than 32 characters. This preset is also configured to use only characters that are easy to type on the standard iOS keyboard, i.e. those appearing on the letters keyboard ("ABC") or the numbers keyboard ".?123", and not those on the harder to reach symbols keyboard "#+=".

  Sample Password:

      -25,favor,MANY,BEAR,53-
      

  Preset Definition:

      {
          padding_alphabet => [qw{- : . ! ? @ &}],
          separator_alphabet => [qw{- : . @}, q{,}, q{ }],
          word_length_min => 4,
          word_length_max => 7,
          num_words => 3,
          separator_character => 'RANDOM',
          padding_digits_before => 2,
          padding_digits_after => 2,
          padding_type => 'FIXED',
          padding_character => 'RANDOM',
          padding_characters_before => 1,
          padding_characters_after => 1,
          case_transform => 'RANDOM',
          allow_accents => 0,
      }
      

• "DEFAULT" - the default configuration.

  Sample Password:

      ~~12:settle:SUCCEED:summer:48~~
      

  Preset Definition:

      {
          symbol_alphabet => [qw{! @ $ % ^ & * - _ + = : | ~ ? / . ;}],
          word_length_min => 4,
          word_length_max => 8,
          num_words => 3,
          separator_character => 'RANDOM',
          padding_digits_before => 2,
          padding_digits_after => 2,
          padding_type => 'FIXED',
          padding_character => 'RANDOM',
          padding_characters_before => 2,
          padding_characters_after => 2,
          case_transform => 'ALTERNATE',
          allow_accents => 0,
      }
      

• "NTLM" - a preset for 14 character NTMLv1 (NTLM Version 1) passwords. ONLY USE THIS PRESET IF YOU MUST! The 14 character limit does not allow for sufficient entropy in scenarios where the attacker knows the dictionary and config used to generate the password. Use of this preset will generate a low entropy warning.

  Sample Password:

      0=mAYAN=sCART@
      

  Preset Definition:

      {
          padding_alphabet => [qw{! @ $ % ^ & * + = : | ~ ?}],
          separator_alphabet => [qw{- + = . * _ | ~}, q{,}],
          word_length_min => 5,
          word_length_max => 5,
          num_words => 2,
          separator_character => 'RANDOM',
          padding_digits_before => 1,
          padding_digits_after => 0,
          padding_type => 'FIXED',
          padding_character => 'RANDOM',
          padding_characters_before => 0,
          padding_characters_after => 1,
          case_transform => 'INVERT',
          allow_accents => 0,
      }
      

• "SECURITYQ" - a preset for creating fake answers to security questions. This preset generates long nonsense sentences ending in "." "!" or "?".

  Sample 'Password':

      Wales outside full month minutes gentle?
      

  Preset Definition:

      {
          word_length_min => 4,
          word_length_max => 8,
          num_words => 6,
          separator_character => q{ },
          padding_digits_before => 0,
          padding_digits_after => 0,
          padding_type => 'FIXED',
          padding_character => 'RANDOM',
          padding_alphabet => [qw{. ! ?}],
          padding_characters_before => 0,
          padding_characters_after => 1,
          case_transform => 'NONE',
          allow_accents => 0,
      }
      

• "WEB16" - a preset for websites that don't allow passwords to be longer than 16 characters. ONLY USE THIS PRESET IF YOU MUST! The 14 character limit does not allow for sufficient entropy in scenarios where the attacker knows the dictionary and config used to generate the password. Use of this preset will generate a low entropy warning.

  Sample Password:

      tube+NICE+iron+02
      

  Preset Definition:

      {
          symbol_alphabet => [qw{! @ $ % ^ & * - _ + = : | ~ ? / . ;}],
          word_length_min => 4,
          word_length_max => 4,
          num_words => 3,
          separator_character => 'RANDOM',
          padding_digits_before => 0,
          padding_digits_after => 2,
          padding_type => 'NONE',
          case_transform => 'RANDOM',
          allow_accents => 0,
      }
      

• "WEB32" - a preset for websites that don't allow passwords to be longer than 32 characters.

  Sample Password:

      +93-took-CASE-money-AHEAD-31+
      

  Preset Definition:

      {
          padding_alphabet => [qw{! @ $ % ^ & * + = : | ~ ?}],
          separator_alphabet => [qw{- + = . * _ | ~}, q{,}],
          word_length_min => 4,
          word_length_max => 5,
          num_words => 4,
          separator_character => 'RANDOM',
          padding_digits_before => 2,
          padding_digits_after => 2,
          padding_type => 'FIXED',
          padding_character => 'RANDOM',
          padding_characters_before => 1,
          padding_characters_after => 1,
          case_transform => 'ALTERNATE',
          allow_accents => 0,
      }
      

• "WIFI" - a preset for generating 63 character long WPA2 keys (most routers allow 64 characters, but some only allow 63, hence the somewhat unexpected length).

  Sample Password:

      2736_ITSELF_PARTIAL_QUICKLY_SCOTLAND_wild_people_7441!!!!!!!!!!
      

  Preset Definition:

      {
          padding_alphabet => [qw{! @ $ % ^ & * + = : | ~ ?}],
          separator_alphabet => [qw{- + = . * _ | ~}, q{,}],
          word_length_min => 4,
          word_length_max => 8,
          num_words => 6,
          separator_character => 'RANDOM',
          padding_digits_before => 4,
          padding_digits_after => 4,
          padding_type => 'ADAPTIVE',
          padding_character => 'RANDOM',
          pad_to_length => 63,
          case_transform => 'RANDOM',
          allow_accents => 0,
      }
      

• "XKCD" - a preset inspired by the original XKCD comic (<http://xkcd.com/936/>), but with some alterations to provide sufficient entropy to avoid low entropy warnings.

  Sample Password:

      quiet-children-OCTOBER-today-HOPE
      

  Preset Definition:

      {
          word_length_min => 4,
          word_length_max => 8,
          num_words => 5,
          separator_character => q{-},
          padding_digits_before => 0,
          padding_digits_after => 0,
          padding_type => 'NONE',
          case_transform => 'RANDOM',
          allow_accents => 0,
      }
      

FUNCTIONAL INTERFACE

There is only a single function exported by the module:

hsxkpasswd()

    my $password = hsxkpasswd();

This function call is equivalent to the following Object-Oriented code:

    my $password =  Crypt::HSXKPasswd->new()->password();

This function passes all arguments it receives through to the constructor, so all arguments that are valid in "new()" are valid here.

This function Croaks if there is a problem generating the password.

Note that it is inefficient to use this function to generate multiple passwords because the dictionary will be re-loaded, and the entropy stats re-calculated each time the function is called.

CONSTRUCTOR

    # create a new instance with the default dictionary, config, and random
    # number generator
    my $hsxkpasswd_instance = Crypt::HSXKPasswd->new();
    
    # the constructor takes optional named arguments, these can be used to
    # customise the word source, config, and random number source.
    
    # create an instance that uses the UNIX words file as the word source
    my $hsxkpasswd_instance = Crypt::HSXKPasswd->new(
        dictionary => Crypt::HSXKPasswd::Dictionary::System->new()
    );
    
    # create an instance that uses an array reference as the word source
    my $hsxkpasswd_instance = Crypt::HSXKPasswd->new(dictionary_list => $array_ref);
    
    # create an instance that uses a dictionary file as the word source
    my $hsxkpasswd_instance = Crypt::HSXKPasswd->new(
        dictionary_file => 'sample_dict_EN.txt'
    );
    
    # the class Crypt::HSXKPasswd::Dictionary::Basic can be used to aggregate
    # multiple array refs and/or dictionary files into a single word source
    my $dictionary = Crypt::HSXKPasswd::Dictionary::Basic->new();
    $dictionary->add_words('dict1.txt');
    $dictionary->add_words('dict2.txt');
    $dictionary->add_words($array_ref);
    my $hsxkpasswd_instance = Crypt::HSXKPasswd->new(dictionary => $dictionary);
    
    # create an instance from the preset 'XKCD'
    my $hsxkpasswd_instance = Crypt::HSXKPasswd->new(preset => 'XKCD');
    
    # create an instance based on the preset 'XKCD' with one customisation
    my $hsxkpasswd_instance = Crypt::HSXKPasswd->new(
        preset => 'XKCD',
        preset_override => {separator_character => q{ }}
    );
    
    # create an instance from a config based on a preset
    # but with many alterations
    my $config = Crypt::HSXKPasswd->preset_config('XKCD');
    $config->{separator_character} = q{ };
    $config->{case_transform} = 'INVERT';
    $config->{padding_type} = "FIXED";
    $config->{padding_characters_before} = 1;
    $config->{padding_characters_after} = 1;
    $config->{padding_character} = '*';
    my $hsxkpasswd_instance = Crypt::HSXKPasswd->new(config => $config);
    
    # create an instance from an entirely custom configuration
    my $config = {
        padding_alphabet => [qw{! @ $ % ^ & * + = : ~ ?}],
        separator_alphabet => [qw{- + = . _ | ~}],
        word_length_min => 6,
        word_length_max => 6,
        num_words => 3,
        separator_character => 'RANDOM',
        padding_digits_before => 2,
        padding_digits_after => 2,
        padding_type => 'FIXED',
        padding_character => 'RANDOM',
        padding_characters_before => 2,
        padding_characters_after => 2,
        case_transform => 'CAPITALISE',
    }
    my $hsxkpasswd_instance = Crypt::HSXKPasswd->new(config => $config);
    
    # create an instance from an entire custom config passed as a JSON string
    # a convenient way to use configs generated using the web interface at
    # https://xkpasswd.net
    my $config = <<'END_CONF';
    {
     "num_words": 4,
     "word_length_min": 4,
     "word_length_max": 8,
     "case_transform": "RANDOM",
     "separator_character": " ",
     "padding_digits_before": 0,
     "padding_digits_after": 0,
     "padding_type": "NONE",
    }
    END_CONF
    my $hsxkpasswd_instance = Crypt::HSXKPasswd->new(config_json => $config);
    
    # create an instance which uses /dev/urandom as the RNG
    # (only possible on Linux/Unix only systems)
    my $hsxkpasswd_instance = Crypt::HSXKPasswd->new(
        rng => Crypt::HSXKPasswd::RNG::DevUrandom->new();
    );
    
    # create an instance which uses Random.Org as the random number generator
    # NOTE - this should be used sparingly, and only by the paranoid. If you
    # abuse this RNG your IP will get blacklisted on Random.Org. You must pass
    # a valid email address to the constructor for
    # Crypt::HSXKPasswd::RNG::RandomDorOrg because Random.Org's usage
    # guidelines request that all invocations to their API contain a contact
    # email in the useragent header, and this module honours that request.
    my $hsxkpasswd_instance = Crypt::HSXKPasswd->new(
        rng => Crypt::HSXKPasswd::RNG::RandomDorOrg->new('your.email@addre.ss');
    );

The constructor must be called via the package name.

If called with no arguments the constructor will use an instance of "Crypt::HSXKPasswd::Dictionary::EN" as the word source, the preset "DEFAULT", and an instance of the class "Crypt::HSXKPasswd::RNG::Basic" to generate random numbers.

The function accepts named arguments to allow for custom specification of the word source, config, and random number source.

Specifying Custom Word Sources

Three named arguments can be used to specify a word source, but only one should be specified at a time. If multiple are specified, the one with the highest priority will be used, and the rest ignored. The variables are listed below in descending order of priority:

• "dictionary" - an instance of a class that extends "Crypt::HSXKPasswd::Dictionary".
• "dictionary_list" - a reference to an array containing words as scalars.
• "dictionary_file" - the path to a dictionary file. Dictionary files should contain one word per. Lines starting with a # symbol will be ignored. It is assumed files will be UTF-8 encoded. If not, a second named argument, "dictionary_file_encoding", can be used to specify another encoding.

Specifying Custom Password Generator Configurations

Two primary named arguments can be used to specify the config the instance should use to generate passwords. Only one should be specified at a time. If multiple are specified, the one with the highest priority will be used, and the rest ignored. The variables are listed below in descending order of priority:

• "config" - a valid config hashref.
• "config_json" - a JSON string representing a valid config hashref.

  This named argument provides a convenient way to use configs generated using the web interface at <https://xkpasswd.net/>. The Save/Load tab in that interface saves and loads configs in JSON format.

• "preset" - a valid preset name. If this variable is used, then any desired config overrides can be passed as a hashref using the variable "preset_overrides".

Specifying Custom Random Number Generators

A custom RNG can be specified using the named argument "rng". The passed value must be an instance of a class that extends "Crypt::HSXKPasswd::RNG" and overrides the function "random_numbers()".

INSTANCE METHODS

->config()

    my $config = $hsxkpasswd_instance->config(); # getter
    $hsxkpasswd_instance->config($config_hashref); # setter
    $hsxkpasswd_instance->config($config_json_string); # setter

When called with no arguments the function returns a clone of the instance's config hashref.

When called with a single argument the function sets the config of the instance to a clone of the passed config. If present, the argument must be either a hashref containing valid config keys and values, or a JSON string representing a hashref containing valid config keys and values.

The function will croak if an invalid config is passed.

->config_as_json()

    my $config_json_string = $hsxkpasswd_instance->config_as_json();

This function returns the content of the instance's loaded config hashref as a JSON string.

The output from this function can be loaded into the web interface at <https://xkpasswd.net> (using the load/save tab).

->config_as_string()

    my $config_string = $hsxkpasswd_instance->config_as_string();

This function returns the content of the instance's loaded config hashref as a scalar string.

->dictionary()

    my $dictionary_clone = $hsxkpasswd_instance->dictionary();
    $hsxkpasswd_instance->dictionary($dictionary_instance);
    $hsxkpasswd_instance->dictionary($array_ref);
    $hsxkpasswd_instance->dictionary('sample_dict_EN.txt');
    $hsxkpasswd_instance->dictionary('sample_dict_EN.txt', 'Latin1');

When called with no arguments this function returns a clone of the currently loaded dictionary which will be an instance of a class that extends "Crypt::HSXKPasswd::Dictionary".

To load a new dictionary into an instance, call this function with arguments. The first argument argument can be an instance of a class that extends "Crypt::HSXKPasswd::Dictionary", a reference to an array of words, or the path to a dictionary file. If either an array reference or a file path are passed, they will be used to instantiate an instance of the class "Crypt::HSXKPasswd::Dictionary::Basic", and that new instance will then be loaded into the object. If a file path is passed, it will be assumed to be UTF-8 encoded. If not, an optional second argument can be passed to specify the file's encoding.

->password()

    my $password = $hsxkpasswd_instance->password();

This function generates a random password based on the instance's loaded config and returns it as a scalar. The function takes no arguments.

The function croaks if there is an error generating the password. The most likely cause of and error is the random number generation, particularly if the loaded random generation function relies on a cloud service or a non-standard library.

->passwords()

    my @passwords = $hsxkpasswd_instance->passwords(10);

This function generates a number of passwords and returns them all as an array.

The function uses "password()" to generate the passwords, and hence will croak if there is an error generating any of the requested passwords.

->passwords_json()

    my $json_string = $hsxkpasswd_instance->passwords_json(10);

This function generates a number of passwords and returns them and the instance's entropy stats as a JSON string representing a hashref containing an array of passwords indexed by "passwords", and a hashref of entropy stats indexed by "stats". The stats hashref itself is indexed by: "password_entropy_blind", "password_permutations_blind", "password_entropy_blind_min", "password_entropy_blind_max", "password_permutations_blind_max", "password_entropy_seen" & "password_permutations_seen".

The function uses "passwords()" to generate the passwords, and hence will croak if there is an error generating any of the requested passwords.

->rng()

    my $rng_instance = $hsxkpasswd_instance->rng();
    $hsxkpasswd_instance->rng($rng_instance);

When called with no arguments this function returns currently loaded Random Number Generator (RNG) which will be an instance of a class that extends "Crypt::HSXKPasswd::RNG".

To load a new RNG into an instance, call this function with a single argument, an instance of a class that extends "Crypt::HSXKPasswd::RNG".

->stats()

    my %stats = $hsxkpasswd_instance->stats();

This function generates a hash containing stats about the instance indexed by the following keys:

• "dictionary_contains_accents" - 1 if the filtered word list contains accented letters, 0 otherwise.
• "dictionary_filter_length_min" & "dictionary_filter_length_max" - the minimum and maximum word lengths allowed by the dictionary filter (defined by config keys "word_length_min" and "word_length_max")
• "dictionary_source" - the source of the word list loaded into the instance.
• "dictionary_words_filtered" - the number of words loaded from the dictionary file that meet the criteria defined by the loaded config.
• "dictionary_words_percent_available" - the percentage of the words in the dictionary file that are available for use with the loaded config.
• "dictionary_words_total" - the total number of words loaded from the dictionary file.
• "password_entropy_blind_min" - the entropy (in bits) of the shortest password the loaded config can generate from the point of view of a brute-force attacker.
• "password_entropy_blind_max" - the entropy (in bits) of the longest password the loaded config can generate from the point of view of a brute-force attacker.
• "password_entropy_blind" - the entropy (in bits) of the average length of passwords the loaded config can generate from the point of view of a brute-force attacker.
• "password_entropy_seen" - the entropy (in bits) of passwords generated by the instance assuming the dictionary and config are known to the attacker.
• "password_length_min" - the minimum length of passwords generated by the loaded config.
• "password_length_max" - the maximum length of passwords generated by the loaded config.
• "password_permutations_blind_min" - the number of permutations a brute-force attacker would have to try to be sure of cracking the shortest possible passwords generated by this instance. Because this number can be very big, it's returned as a "Math::BigInt" object.
• "password_permutations_blind_max" - the number of permutations a brute-force attacker would have to try to be sure of cracking the longest possible passwords generated by this instance. Because this number can be very big, it's returned as a "Math::BigInt" object.
• "password_permutations_blind" - the number of permutations a brute-force attacker would have to try to be sure of cracking an average length password generated by this instance. Because this number can be very big, it's returned as a "Math::BigInt" object.
• "password_permutations_seen" - the number of permutations an attacker with a copy of the dictionary and config would need to try to be sure of cracking a password generated by this instance. Because this number can be very big, it's returned as a "Math::BigInt" object.
• "passwords_generated" - the number of passwords this instance has generated.
• "password_random_numbers_required" - the number of random numbers needed to generate a single password using the loaded config.
• "randomnumbers_cached" - the number of random numbers currently cached within the instance.
• "randomnumbers_cache_increment" - the number of random numbers generated at once to replenish the cache when it's empty.
• "randomnumbers_source" - the class used by the instance to generate random numbers.

->status()

    print $hsxkpasswd_instance->status();

Generates a string detailing the internal status of the instance. Below is a sample status string:

    *DICTIONARY*
    Source: Crypt::HSXKPasswd::Dictionary::EN
    # words: 1425
    # words of valid length: 1194 (84%)
    
    *CONFIG*
    case_transform: 'ALTERNATE'
    num_words: '3'
    padding_character: 'RANDOM'
    padding_characters_after: '2'
    padding_characters_before: '2'
    padding_digits_after: '2'
    padding_digits_before: '2'
    padding_type: 'FIXED'
    separator_alphabet: ['!', '$', '%', '&', '*', '+', '-', '.', '/', ':', ';', '=', '?', '@', '^', '_', '|', '~']
    separator_character: 'RANDOM'
    symbol_alphabet: ['!', '$', '%', '&', '*', '+', '-', '.', '/', ':', ';', '=', '?', '@', '^', '_', '|', '~']
    word_length_max: '8'
    word_length_min: '4'
    
    *RANDOM NUMBER CACHE*
    Random Number Generator: Crypt::HSXKPasswd::RNG::Basic
    # in cache: 0
    
    *PASSWORD STATISTICS*
    Password length: between 24 & 36
    Permutations (brute-force): between 2.91x10^47 & 1.57x10^71 (average 2.14x10^59)
    Permutations (given dictionary & config): 5.51x10^15
    Entropy (Brute-Force): between 157bits and 236bits (average 197bits)
    Entropy (given dictionary & config): 52bits
    # Random Numbers needed per-password: 9
    Passwords Generated: 0

->update_config()

    $hsxkpasswd_instance->update_config({separator_character => '+'});

The function updates the config within an HSXKPasswd instance. A hashref with the config options to be changed must be passed. The function returns a reference to the instance to enable function chaining. The function will croak if the updated config would be invalid in some way. Note that if this happens the running config will not have been altered in any way.

CLASS METHODS

clone_config()

    my $clone = Crypt::HSXKPasswd->clone_config($config);

This function must be passed a valid config hashref as the first argument or it will croak. The function returns a hashref.

config_key_definition()

    my %key_definition = Crypt::HSXKPasswd->config_key_definition($key_name);

A function to return the definition for a config key. The definition is returned as a hash indexed by the following keys:

• "required" - 1 if the key is a required key, and 0 otherwise.
• "type" - a "Type::Tiny" object representing the valid data type for the key.
• "expects" - an English description of valid values for the key.

config_key_definitions()

    my %key_definitions = Crypt::HSXKPasswd->config_key_definitions();

A function to return definitions for all defined config keys as a hash indexed by config key names. Each definition is represented as a hash with the same keys as the hashes returned by the function "config_key_definition()".

config_stats()

    my %stats = Crypt::HSXKPasswd->config_stats($config);
    my %stats = Crypt::HSXKPasswd->config_stats(
        $config,
        suppress_warnings => 1,
    );

This function requires one argument, a valid config hashref. It returns a hash of statistics about a given configuration. The hash is indexed by the following:

• "length_min" - the minimum length a password generated with the given config could be.
• "length_max" - the maximum length a password generated with the given config could be. (see caveat below)
• "random_numbers_required" - the amount of random numbers needed to generate a password using the given config.

There is one scenario in which the calculated maximum length will not be reliably accurate, and that's when a character substitution with a length greater than 1 is specified, and "padding_type" is not set to "ADAPTIVE". If the config passed contains such a character substitution, the length will be calculated ignoring the possibility that one or more extra characters could be introduced depending on how many, if any, of the long substitutions get triggered by the randomly chosen words. If this happens the function will also carp with a warning. Such warnings can be suppressed by passing an optional named argument "suppress_warnings" with the value 1.

config_to_json()

    my $config_json_string = Crypt::HSXKPasswd->config_to_json($config);

This function returns a JSON representation of the passed config hashref as a scalar string.

The function must be passed a valid config hashref or it will croak.

config_to_string()

    my $config_string = Crypt::HSXKPasswd->config_to_string($config);

This function returns the content of the passed config hashref as a scalar string. The function must be passed a valid config hashref or it will croak.

default_config()

    my $config = Crypt::HSXKPasswd->default_config();

This function returns a hashref containing a config with default values.

This function can optionally be called with a single argument, a hashref containing keys with values to override the defaults with.

    my $config = Crypt::HSXKPasswd->default_config({num_words => 3});

When overrides are present, the function will carp if an invalid key or value is passed, and croak if the resulting merged config is invalid.

This function is a shortcut for "preset_config()", and the two examples above are equivalent to the following:

    my $config = Crypt::HSXKPasswd->preset_config('DEFAULT');
    my $config = Crypt::HSXKPasswd->preset_config('DEFAULT', {num_words => 3});

defined_config_keys()

    my @config_key_names = Crypt::HSXKPasswd->defined_config_keys();

This function returns the list of valid config key names as an array of strings.

defined_presets()

    my @preset_names = Crypt::HSXKPasswd->defined_presets();

This function returns the list of defined preset names as an array of strings.

distil_to_config_keys()

    my $dist_hashref = Crypt::HSXKPasswd->distil_to_config_keys($hashref);

This function takes a hashref as an argument, and returns a deep clone of that hashref containing only valid config keys with valid values.

By default the function silently drops keys that are not valid config keys, but issues a warning when dropping a key that is a valid config key, but contains an invalid value. The function can also issue warnings when dropping keys that are not valid config keys.

The warnings can be controlled with a pair of optional named arguments that can be added as a second argument:

    # suppress all warnings
    my $dist_hashref = Crypt::HSXKPasswd->distil_to_config_keys(
        $hashref,
        suppress_warnings => 1,
    );
    
    # emit warnings when dropping invalidly named keys
    my $dist_hashref = Crypt::HSXKPasswd->distil_to_config_keys(
        $hashref,
        warn_invalid_key_names => 1,
    );

distil_to_symbol_alphabet()

    my @unique_syms = Crypt::HSXKPasswd->distil_to_symbol_alphabet($arrayref);
    my @unique_syms = Crypt::HSXKPasswd->distil_to_symbol_alphabet(
        $arrayref,
        warn => 1,
    );

This function takes reference to an array of strings and returns a new array containing all the valid symbols from the referenced array. The valid symbols are de-duplicated before being returned.

By default the function silently skips over strings that are not valid symbols. The function can be made issue warnings each time a string is skipped by passing a named argument "warn" with a value of 1 (0 can also be passed to explicitly disable warnings).

distil_to_words()

    my @valid_unique_words = Crypt::HSXKPasswd->distil_to_words($arrayref);
    my @valid_unique_words = Crypt::HSXKPasswd->distil_to_words(
        $arrayref,
        warn => 1,
    );

This function takes reference to an array of strings and returns a new array containing all the valid words from the referenced array. The valid words are de-duplicated before being returned.

By default the function silently skips over strings that are not valid words. The function can be made issue warnings each time a string is skipped by passing a named argument "warn" with a value of 1 (0 can also be passed to explicitly disable warnings).

is_valid_config()

    # determine the validity
    my $is_ok = Crypt::HSXKPasswd->is_valid_config($config);
    
    # assert the validity - will croak if the config is invalid
    Crypt::HSXKPasswd->is_valid_config($config, croak => 1);

This function must be passed a hashref to test as the first argument. The function returns 1 if the passed config is valid, and 0 otherwise.

Optionally, a named argument "croak" can also be passed to control whether or not the function should croak if the config is invalid. The value of this named argument should be 1 or 0.

When calling the function with "croak" set to 1, the message thrown by croak will explain why the config is invalid.

    use English qw( -no_match_vars );
    eval{
        Crypt::HSXKPasswd->is_valid_config($config, croak => 1);
    }or do{
        print "ERROR - config is invalid because: $EVAL_ERROR\n";
    }

module_config()

    my $debug_val = Crypt::HSXKPasswd->module_config('DEBUG'); # getter
    Crypt::HSXKPasswd->module_config('DEBUG', 1); # setter

This function is used to access or alter the value of one of the module configuration settings. The first function must always be a valid module configuration key name. If no second argument is provided, the value stored in the module configuration key will not be updated. To update the stored value, pass a new value as a second argument. Regardless of whether or not a second argument is passed, the value stored in the module configuration key is always returned.

The function will croak if called with an invalid module configuration key name, or passed an invalid new value.

For a list of the module configuration keys, see the MODULE CONFIGURATION section of this document.

preset_config()

    my $config = Crypt::HSXKPasswd->preset_config('XKCD');

This function returns the config hashref for a given preset. See above for the list of available presets.

The first argument this function accepts is the name of the desired preset as a scalar. If an invalid name is passed, the function will carp. If no preset is passed the preset "DEFAULT" is assumed.

This function can optionally accept a second argument, a hashref containing keys with values to override the defaults with.

    my $config = Crypt::HSXKPasswd->preset_config(
        'XKCD',
        {case_transform => 'INVERT'}
    );

When overrides are present, the function will carp if an invalid key or value is passed, and croak if the resulting merged config is invalid.

preset_definition()

    my %preset_def = Crypt::HSXKPasswd->preset_definition('XKCD');

This function returns a hash defining a preset. The hash contains an English description of the preset indexed be "description" and a config hashref indexed by "config".

The function expects to be called with one argument, a valid preset name, but it can be called without arguments, in which case it will return the definition for the preset c<DEFAULT>.

You can see all the defined presets in the PRESETS section of this document, and you can get a list of valid preset names programatically with the function "defined_presets()".

preset_definitions()

    my %preset_defs = Crypt::HSXKPasswd->preset_definitions();

This function returns a hash of all defined presets indexed by preset name. Each preset definition is a hash as returned by "preset_definition()".

This function does not take any arguments.

presets_json()

    my $json_string = Crypt::HSXKPasswd->presets_json();

This function returns a JSON string representing all the defined configs, including their descriptions.

The returned JSON string represents a hashref indexed by three keys: "defined_keys" contains an array of preset identifiers, "presets" contains the preset configs indexed by reset identifier, and "preset_descriptions" contains a hashref of descriptions indexed by preset identifiers.

preset_description()

    my $description = Crypt::HSXKPasswd->preset_description('XKCD');

This function returns the description for a given preset. See above for the list of available presets.

The first argument this function accepts is the name of the desired preset as a scalar. If an invalid name is passed, the function will carp. If no preset is passed the preset "DEFAULT" is assumed.

presets_to_string()

    print Crypt::HSXKPasswd->presets_to_string();

This function returns a string containing a description of each defined preset and the configs associated with the presets.

COMMANDLINE INTERFACE

This interface allows for the generation of multiple passwords at a time, the use of presets and preset overrides, the use of custom password generator configurations, the use of custom word sources, and the use of custom random number generators.

Both preset overrides and password generator configurations must be specified in JSON format.

Examples

Generate a single password using all the default settings:

    hsxkpasswd

Generate five passwords using the default settings:

    hsxkpasswd 5

Generate five passwords using the "XKCD" preset:

    hsxkpasswd -p XKCD 5

Generate five passwords using the "XKCD" preset with an overridden password generator configuration key:

    hsxkpasswd -p XKCD -o '{"separator_character" : "*"}' 5

Generate five passwords using a custom password generator configuration stored in a text file in JSON format:

    hsxkpasswd -c my_config.json

Further Reading

The examples above are just a sample of what the command can do, for complete documentation, run the command with the -h flag:

    hsxkpasswd -h

If you are new to JSON, you may find the following links useful:

• JSON on Wikipedia - <http://en.wikipedia.org/wiki/JSON>
• A free online JSON validator - <http://jsonformatter.curiousconcept.com>
• A JSON tutorial from W3Schools - <http://www.w3schools.com/json/>

ENTROPY CHECKING

Entropy is calculated and checked for two scenarios. Firstly, for the best-case scenario, when an attacker has no prior knowledge about the password, and must resort to a brute-force attack. And secondly, for the worst-case scenario, when the attacker is assumed to know that this module was used to generate the password, and, that the attacker has a copy of the word source and config settings used to generate the password.

Entropy checking is controlled via three module configuration variables (which can be accessed and updated using the function "module_config()"):

• "ENTROPY_MIN_BLIND" - the minimum acceptable entropy in bits for a brute-force attack. The default value is 78bits, the equivalent to a 12 character password consisting of mixed-case letters, digits, and symbols.
• "ENTROPY_MIN_SEEN" - the minimum acceptable entropy in bits for a worst-case scenario (where the word source and config are known). The default value is 52bits, equivalent to an 8 character password consisting of mixed-case letters, digits, and symbols.
• "ENTROPY_WARNINGS" - this variable can be used to control the emission of entropy warnings. The following values are valid:

Caveats

The entropy calculations make some assumptions which may in some cases lead to the results being inaccurate. In general, an attempt has been made to always round down, meaning that in reality the entropy of the produced passwords may be higher than the values calculated by the package.

When calculating the entropy for brute force attacks on configurations that can result in variable length passwords, the shortest possible password is assumed.

When calculating the entropy for brute force attacks on configurations that contain at least one symbol, it is assumed that an attacker would have to brute-force-check 33 symbols. This is the same value used by Steve Gibson's Password Haystacks calculator (<https://www.grc.com/haystack.htm>).

When calculating the entropy for worst-case attacks on configurations that contain symbol substitutions where the replacement is more than 1 character long the possible extra length is ignored.

WORD SOURCES (DICTIONARIES)

In order to produce secure passwords it's important to use a word source that contains a large selection of words with a good mix of different lengths of words.

The module ships with a number of pre-defined word sources:

"Crypt::HSXKPasswd::Dictionary::DE"

A German word list based on the GPL-licensed German dictionary for WinEdit by Juergen Vierheilig.

Note: This module is licensed under the GPL, not the BSD license used for the majority of this project.

"Crypt::HSXKPasswd::Dictionary::EN"

A default word list consisting of English words and place names.

"Crypt::HSXKPasswd::Dictionary::ES"

A Spanish word list based on the BSD-licensed Spanish dictionary for WinEdit by Juan L. Varona from the Universidad de La Rioja.

"Crypt::HSXKPasswd::Dictionary::FR"

A French word list based on the GPL-licensed French dictionary for WinEdit.

Note: This module is licensed under GPL V2, not the BSD license used for the majority of this project.

"Crypt::HSXKPasswd::Dictionary::IT"

An Italian word list based on the free-for-non-commerical-use Italian dictionary for WinEdit by Karl Koeller.

Note: This module is licensed under GPL V2, not the BSD license used for the majority of this project.

"Crypt::HSXKPasswd::Dictionary::NL"

A Dutch/Flemish word list based on the GPL-licensed Dutch dictionary for WinEdit.

Note: This module is licensed under GPL V2, not the BSD license used for the majority of this project.

"Crypt::HSXKPasswd::Dictionary::PT"

A Portuguese word list based on the GPL-licensed Portuguese dictionary for WinEdit compiled by Bernhard Enders (building on work by Raimundo Santos Moura & Ricardo Ueda Karpischek).

Note: This module is licensed under GPL V2.1, not the BSD license used for the majority of this project.

"Crypt::HSXKPasswd::Dictionary::System"

This class tries to find and use a Unix words file on the system.

The constructor croaks if no system words file can be found.

Usage

    my $word_source = Crypt::HSXKPasswd::Dictionary::System->new();

"Crypt::HSXKPasswd::Dictionary::Basic"

This class can be initialised from a words file, or from an array ref containing words.

Usage

    my $word_source = Crypt::HSXKPasswd::Dictionary::Basic->new('file_path');
    my $word_source = Crypt::HSXKPasswd::Dictionary::Basic->new(
        'file_path',
        'Latin1'
    );
    my $word_source = Crypt::HSXKPasswd::Dictionary::Basic->new($array_ref);

The rules for the formatting of dictionary files are simple. Dictionary files must contain one word per line. Words shorter than four letters will be ignored, as will all lines starting with the # symbol. Files are assumed to be UTF-8 encoded, but an optional second argument can be passed specifying a different file encoding.

This format is the same as that of the standard Unix Words file, usually found at "/usr/share/dict/words" on Unix and Linux operating systems (including OS X).

RANDOM NUMBER SOURCES

The module can use an instance of any class that extends "Crypt::HSXKPasswd::RNG" as it's source of randomness. Custom RNG classes must implement the method "random_numbers()" which will be invoked on an instance of the class and passed one argument, the number of random numbers required to generate a single password. The function must return an array of random numbers between 0 and 1. The number of random numbers returned is entirely up to the module to decide. The number required for a single password is passed purely as a guide. The function must always return at least one random number.

The module ships with five standard RNGs (described below).

By default, the module will try to use one of the following four RNGs, listed from most to least preferred, depending on what is available on the system:

1.

"Crypt::HSXKPasswd::RNG::Math_Random_Secure" (only available if "Math::Random::Secure" is installed on the system).

2.

"Crypt::HSXKPasswd::RNG::Data_Entropy" (only available if "Data::Entropy::Algorithms" is installed on the system).

3.

"Crypt::HSXKPasswd::RNG::DevUrandom" (only available on Linux/Unix systems with a "/dev/urandom").

4.

"Crypt::HSXKPasswd::RNG::Basic" (available on all systems because it uses Perl's built-in "rand()" function).

If the constructor is called without specifying an RNG, and if the only available RNG is "Crypt::HSXKPasswd::RNG::Basic", a warning will be thrown suggesting installing "Math::Random::Secure" or "Data::Entropy::Algorithms".

The module also ships with a fifth RNG, "Crypt::HSXKPasswd::RNG::RandomDotOrg", but this one must be explicitly used, the constructor will never used it by default. As its name suggests, this class uses <http://Random.Org/>'s HTTP API to generate random numbers.

To explicitly use any particular RNG, create an instance of it, and either pass that instance to the constructor with the named argument "rng", or, set the RNG after instantiating the object using the "rng()" function.

Crypt::HSXKPasswd::RNG::Math_Random_Secure

    my $rng = Crypt::HSXKPasswd::RNG::Math_Random_Secure->new();

This is the preferred RNG because it is both fast and secure, but, it requires the non-standard module "Math::Random::Secure" (<http://search.cpan.org/perldoc?Math%3A%3ARandom%3A%3ASecure>) be installed.

Crypt::HSXKPasswd::RNG::Data_Entropy

    my $rng = Crypt::HSXKPasswd::RNG::Data_Entropy->new();

This RNG is secure, but it is quite slow (about six times slower than "Crypt::HSXKPasswd::RNG::Math_Random_Secure"), and it requires the non-standard module "Data::Entropy::Algorithms" (<http://search.cpan.org/perldoc?Data%3A%3AEntropy%3A%3AAlgorithms>) be installed.

Crypt::HSXKPasswd::RNG::DevUrandom

    my $rng = Crypt::HSXKPasswd::RNG::DevUrandom->new();

This RNG is secure and relatively fast (faster than "Crypt::HSXKPasswd::RNG::Data_Entropy" but slower than "Crypt::HSXKPasswd::RNG::Math_Random_Secure"), but is only available on Linux/Unix systems with a "/dev/urandom" special file.

Crypt::HSXKPasswd::RNG::Basic

    my $rng = Crypt::HSXKPasswd::RNG::Basic->new();

This RNG uses Perl's built-in "rand()" function as its source of randomness, and this is sub-optimal. The Perl docs warn that "rand()" is not a particularly good source of random numbers, and advises against its use for cryptography.

This RNG provides a base-line, and should only be used if none of the better RNGs are available. While it is sub-optimal, it will still generate passwords with sufficient entropy in most situations. Ultimately, even using this imperfect RNG, this module will still produce passwords that are much better than those produced by the human imagination!

Crypt::HSXKPasswd::RNG::RandomDotOrg

    my $rng = Crypt::HSXKPasswd::RNG::RandomDotOrg->new('my.address@my.dom');
    my $rng = Crypt::HSXKPasswd::RNG::RandomDotOrg->new('my.address@my.dom',
        timeout => 180,
        num_passwords => 3,
    );

This RNG serves as a usable example of an RNG that queries a web service. As its name suggests, this class uses <http://Random.Org/>'s HTTP API to generate random numbers.

In order to comply with Random.Org's client guidelines (<https://www.random.org/clients/>), this module requires that a valid email address be passed as the first argument.

The client guidelines also request that clients use long timeouts, and batch their requests. They prefer to be asked for more number less frequently than less numbers more frequently. For this reason the class's default behaviour is to use a timeout of 180 seconds, and to request enough random numbers to generate three passwords at a time.

These defaults can be overridden by passing named arguments to the constructor after the email address. The following named arguments are supported:

• "timeout" - the timeout to use when making HTTP requests to Random.Org in seconds (the default is 180).
• "num_passwords" - the number of password generations to fetch random numbers for per request from Random.org. This value is in effect a multiplier for the value passed to the "random_numbers()" function by "Crypt::HSXKPasswd".

  "num_absolute" - the absolute number of random numbers to fetch per request to Random.Org. This argument takes precedence over "num_passwords".

"num_passwords" and "num_absolute" should not be used together, but if they are, "num_absolute" use used, and "num_passwords" is ignored.

This class requires a number of modules not used by any other classes under "Crypt::HSXKPasswd", and not listed in that module's requirements. If all of the following modules are not installed, the constructor will croak:

• "Email::Valid"
• "LWP::UserAgent"
• "Mozilla::CA"
• "URI"