3 # Password history via Heimdal external strength checking.
5 # This script is meant to be called via the Heimdal external password strength
6 # checking interface and maintains per-user password history. Password
7 # history is stored as Crypt::PBKDF2 hashes with random salt for each
10 # Written by Russ Allbery <eagle@eyrie.org>
11 # Copyright 2013, 2014
12 # The Board of Trustees of the Leland Stanford Junior University
14 ##############################################################################
15 # Declarations and configuration
16 ##############################################################################
25 use Fcntl qw(O_CREAT O_RDWR);
26 use File::Basename qw(basename);
27 use Getopt::Long::Descriptive qw(describe_options);
29 use JSON qw(encode_json decode_json);
30 use POSIX qw(setgid setuid);
32 use Sys::Syslog qw(openlog syslog LOG_AUTH LOG_INFO LOG_WARNING);
34 # The most convenient interface to Berkeley DB files is ties.
35 ## no critic (Miscellanea::ProhibitTies)
37 # The number of PBKDF2 iterations to use when hashing passwords. This number
38 # should be chosen so as to force the hash operation to take approximately 0.1
39 # seconds on current hardware.
40 Readonly my $HASH_ITERATIONS => 14592;
42 # Path to the history database. Currently, this must be a Berkeley DB file in
43 # the old DB_HASH format. Keys will be principal names, and values will be a
44 # JSON array of hashes. Each hash will have two keys: timestamp, which holds
45 # the seconds since UNIX epoch at which the history entry was stored, and
46 # hash, which holds the Crypt::PBKDF2 LDAP-style password hash.
47 Readonly my $HISTORY_PATH => '/var/lib/heimdal-history/history.db';
49 # User and group used to do all password history lookups and writes, assuming
50 # that this program is invoked as root and can therefore change UID and GID.
51 Readonly my $HISTORY_USER => '_history';
52 Readonly my $HISTORY_GROUP => '_history';
54 # Path to the Berkeley DB file (DB_HASH format) that stores statistics on
55 # password length of accepted passwords. Each successful password validation
56 # will increase the counter for that length. This is read and written with
57 # $HISTORY_USER and $HISTORY_GROUP.
58 Readonly my $LENGTH_STATS_PATH => '/var/lib/heimdal-history/lengths.db';
60 # The message to return to the user if we reject the password because it was
61 # found in the user's history.
62 Readonly my $REJECT_MESSAGE => 'password was previously used';
64 # The path to the external strength checking program to run. This is done
65 # first before checking history, and if it fails, that failure is returned as
66 # the failure for this program.
67 Readonly my $STRENGTH_PROGRAM => '/usr/bin/heimdal-strength';
69 # User and group used to do password strength checking. Generally, this
70 # doesn't require any privileges since the strength dictionary is
72 Readonly my $STRENGTH_USER => 'nobody';
73 Readonly my $STRENGTH_GROUP => 'nogroup';
75 ##############################################################################
77 ##############################################################################
79 # Change real and effective UID and GID to those for the given user and group.
80 # Does nothing if not running as root.
82 # $user - User to change the UID to
83 # $group - Group to change the GID to (and clear all supplemental groups)
86 # Throws: Text exception on any failure
88 my ($user, $group) = @_;
90 # If running as root, drop privileges. Fail if we can't get the UID and
91 # GID corresponding to our users.
92 if ($> == 0 || $< == 0) {
93 my $uid = getpwnam($user)
94 or die "$0: cannot get UID for $user\n";
95 my $gid = getgrnam($group)
96 or die "$0: cannot get GID for $group\n";
97 setgid($gid) or die "$0: cannot setgid to $gid: $!\n";
98 setuid($uid) or die "$0: cannot setuid to $uid: $!\n";
99 if ($> == 0 || $< == 0) {
100 die "$0: failed to drop permissions\n";
106 ##############################################################################
108 ##############################################################################
110 # Given a list of keys and values for a log message as a hash reference,
111 # return in encoded format following our logging protocol. The log format is
112 # a set of <key>=<value> parameters separated by a space. Values containing
113 # whitespace are quoted with double quotes, with any internal double quotes
116 # Here also is defined a custom sort order for the encoded key/value pairs to
117 # keep them in a reasonable order for a human to read.
119 # $params_ref - Reference to a hash of key/value pairs
121 # Returns: The encoded format as a string
122 sub encode_log_message {
123 my ($params_ref) = @_;
125 # Define the custom sort order for keys.
128 = map { $_ => $order++ } qw(action principal error result reason);
130 # Build the message from the parameters.
132 for my $key (sort { $order{$a} <=> $order{$b} } keys %{$params_ref}) {
133 my $value = $params_ref->{$key};
134 $value =~ s{ \" }{\"\"}xmsg;
135 if ($value =~ m{ [ \"] }xms) {
136 $value = qq{"$value"};
138 $message .= qq{$key=$value };
144 # Log a non-fatal error encountered while trying to check or store password
145 # history. This is used for errors where the password is accepted, but we ran
146 # into some anomalous event such as corrupted history data that should be
147 # drawn to the attention of an administrator. The log format is a set of
148 # <key>=<value> parameters, with the following keys:
150 # - action: the action performed (currently always "check")
151 # - principal: the principal to check a password for
152 # - error: an error message explaining the anomalous situation
154 # Values containing whitespace are quoted with double quotes, with any
155 # internal double quotes doubled.
157 # $principal - Principal for which we checked a password
158 # $error - The error message
162 my ($principal, $error) = @_;
163 my $message = encode_log_message(
165 principal => $principal,
168 syslog(LOG_WARNING, '%s', $message);
172 # Log the disposition of a particular password strength checking request. All
173 # log messages are logged through syslog at class info. The log format is a
174 # set of <key>=<value> parameters, with the following keys:
176 # - action: the action performed (currently always "check")
177 # - principal: the principal to check a password for
178 # - result: either "accepted" or "rejected"
179 # - reason: the reason for a rejection
181 # Values containing whitespace are quoted with double quotes, with any
182 # internal double quotes doubled.
184 # $principal - Principal for which we checked a password
185 # $result - "accepted" or "rejected" per above
186 # $reason - On rejection, the reason
190 my ($principal, $result, $reason) = @_;
192 # Create the message.
195 principal => $principal,
198 if ($result eq 'rejected' && defined($reason)) {
199 $message{reason} = $reason;
201 my $message = encode_log_message(\%message);
204 syslog(LOG_INFO, '%s', $message);
208 ##############################################################################
210 ##############################################################################
212 # Given a password, return the hash for that password. Hashing is done with
213 # PBKDF2 using SHA-2 as the underlying hash function. As of version 0.133330,
216 # $password - Password to hash
217 # $iterations - Optional iteration count, defaulting to $HASH_ITERATIONS
219 # Returns: Hash encoded in the LDAP-compatible Crypt::PBKDF2 format
221 my ($password, $iterations) = @_;
222 $iterations //= $HASH_ITERATIONS;
223 my $hasher = Crypt::PBKDF2->new(
224 hash_class => 'HMACSHA2',
225 iterations => $iterations,
227 return $hasher->generate($password);
230 # Given a password and the password history for the user as a reference to a
231 # array, check whether that password is found in the history. The history
232 # array is expected to contain anonymous hashes. The only key of interest is
233 # the "hash" key, whose value is expected to be a hash in the LDAP-compatible
234 # Crypt::PBKDF2 format.
236 # Invalid history entries are ignored for the purposes of this check and
237 # treated as if the entry did not exist.
239 # $principal - Principal to check (solely for logging purposes)
240 # $password - Password to check
241 # $history_ref - Reference to array of anonymous hashes with "hash" keys
243 # Returns: True if the password matches one of the history hashes, false
246 my ($principal, $password, $history_ref) = @_;
247 my $hasher = Crypt::PBKDF2->new(hash_class => 'HMACSHA2');
249 # Walk the history looking at each hash key.
250 for my $entry (@{$history_ref}) {
251 my $hash = $entry->{hash};
252 next if !defined($hash);
254 # validate throws an exception if the hash is in an invalid format.
255 # Treat that case the same as a miss, but log it.
256 if (eval { $hasher->validate($hash, $password) }) {
259 log_error($principal, "hash validate failed: $@");
267 ##############################################################################
269 ##############################################################################
271 # Perform a binary search for a number of hash iterations that makes password
272 # hashing take the given target time on the current system.
276 # * The system load is low enough that this benchmark result is meaningful
277 # and not heavily influenced by other programs running on the system. The
278 # binary search may be unstable if the system load is too variable.
280 # * The static "password" string used for benchmarking will exhibit similar
281 # performance to the statistically average password.
283 # Information about the iteration search process is printed to standard output
284 # while the search runs.
286 # $target - The elapsed time, in real seconds, we're aiming for
287 # $delta - The permissible delta around the target time
289 # Returns: The number of hash iterations with that performance characteristic
290 # Throws: Text exception on failure to write to standard output
291 sub find_iteration_count {
292 my ($target, $delta) = @_;
296 # A static password to use for benchmarking.
297 my $password = 'this is a benchmark';
299 # Start at the current configured iteration count. If this doesn't take
300 # long enough, it becomes the new low mark and we try double that
301 # iteration count. Otherwise, do binary search.
303 # We time twenty iterations each time, chosen because it avoids the
304 # warnings from Benchmark about too few iterations for a reliable count.
306 my $iterations = $HASH_ITERATIONS;
308 my $hash = sub { password_hash($password, $iterations) };
309 my $times = Benchmark::timethis(20, $hash, q{}, 'none');
311 # Extract the CPU time from the formatted time string. This will be
312 # the total time for all of the iterations, so divide by the iteration
313 # count to recover the time per iteration.
314 my $report = Benchmark::timestr($times);
315 my ($time) = ($report =~ m{ ([\d.]+) [ ] CPU }xms);
318 # Tell the user what we discovered.
319 say {*STDOUT} "Performing $iterations iterations takes $time seconds"
320 or die "$0: cannot write to standard output: $!\n";
322 # If this is what we're looking for, we're done.
323 if (abs($time - $target) < $delta) {
327 # Determine the new iteration target.
328 if ($time > $target) {
333 if ($time < $target && $high == 0) {
334 $iterations = $iterations * 2;
336 $iterations = int(($high + $low) / 2);
340 # Report the result and return it.
341 say {*STDOUT} "Use $iterations iterations"
342 or die "$0: cannot write to standard output: $!\n";
346 ##############################################################################
348 ##############################################################################
350 # Given a principal and a password, determine whether the password was found
351 # in the password history for that user.
353 # $path - Path to the history file
354 # $principal - Principal for which to check history
355 # $password - Check history for this password
357 # Returns: True if $password is found in history, false otherwise
358 # Throws: On failure to open, lock, or tie the database
360 my ($path, $principal, $password) = @_;
362 # Open and lock the database and retrieve the history for the user.
363 # We have to lock for write so that we can create the database if it
364 # doesn't already exist. Password change should be infrequent enough
365 # and our window is fast enough that it shouldn't matter. We do this
366 # in a separate scope so that the history hash goes out of scope and
367 # is freed and unlocked.
371 my $mode = O_CREAT | O_RDWR;
372 tie(%history, 'DB_File::Lock', [$path, $mode, oct(600)], 'write')
373 or die "$0: cannot open $path: $!\n";
374 $history_json = $history{$principal};
377 # If there is no history for the user, return the trivial false.
378 if (!defined($history_json)) {
382 # Decode history from JSON. If this fails (corrupt history), treat it as
383 # if the user has no history, but log the error message.
384 my $history_ref = eval { decode_json($history_json) };
385 if (!defined($history_ref)) {
386 log_error($principal, "history JSON decoding failed: $@");
390 # Finally, check the password against the hashes in history.
391 return is_in_history($principal, $password, $history_ref);
394 # Write a new history entry to the database given the principal and the
395 # password to record. History records are stored as JSON arrays of objects,
396 # with keys "timestamp" and "hash".
398 # $path - Path to the history file
399 # $principal - Principal for which to check history
400 # $password - Check history for this password
403 # Throws: On failure to open, lock, or tie the database
405 my ($path, $principal, $password) = @_;
407 # Open and lock the database for write.
409 my $mode = O_CREAT | O_RDWR;
410 tie(%history, 'DB_File::Lock', [$path, $mode, oct(600)], 'write')
411 or die "$0: cannot open $path: $!\n";
413 # Read the existing history. If the existing history is corrupt, treat
414 # that as equivalent to not having any history, but log an error.
415 my $history_json = $history{$principal};
417 if (defined($history_json)) {
418 $history_ref = eval { decode_json($history_json) };
420 log_error($principal, "history JSON decoding failed: $@");
423 if (!defined($history_ref)) {
427 # Add a new history entry.
428 my $entry = { timestamp => time(), hash => password_hash($password) };
429 unshift(@{$history_ref}, $entry);
431 # Store the encoded data back in the history database.
432 $history{$principal} = encode_json($history_ref);
434 # The database is closed and unlocked when %history goes out of scope.
435 # Unfortunately, we lose on error detection here, since there doesn't
436 # appear to be a way to determine whether all the writes succeeded. But
437 # losing a bit of history in the rare error case of failing to write to
438 # local disk is probably not a big deal.
442 # Write statistics about password length. Given the length of the password
443 # and the path to the length statistics database, increments the counter for
444 # that password length.
446 # Any failure to open or write to the database is ignored, since this is
447 # considered optional logging and should not block the password change.
449 # $path - Path to the length statistics file
450 # $length - Length of the accepted password
453 sub update_length_counts {
454 my ($path, $length) = @_;
456 # Open and lock the database for write.
458 my $mode = O_CREAT | O_RDWR;
459 tie(%lengths, 'DB_File::Lock', [$path, $mode, oct(600)], 'write')
462 # Write each of the hashes.
465 # The database is closed and unlocked when %lengths goes out of scope.
469 ##############################################################################
470 # Heimdal password quality protocol
471 ##############################################################################
473 # Run another external password quality checker and return the results. This
474 # allows us to chain to another program that handles the actual strength
475 # checking prior to handling history.
477 # $principal - Principal attempting to change their password
478 # $password - The new password
480 # Returns: Scalar context: true if the password was accepted, false otherwise
481 # List context: whether the password is okay, the exit status of the
482 # quality checking program, and the error message if the first
484 # Throws: Text exception on failure to execute the program, or read or write
485 # from it or to it, or if it fails without an error
487 my ($principal, $password) = @_;
489 # Run the external quality checking program. If we're root, we'll run it
490 # as the strength checking user and group.
491 my $in = "principal: $principal\nnew-password: $password\nend\n";
492 my $init = sub { drop_privileges($STRENGTH_USER, $STRENGTH_GROUP) };
494 run([$STRENGTH_PROGRAM, $principal], \$in, \$out, \$err, init => $init);
495 my $status = ($? >> 8);
498 my $okay = ($status == 0 && $out eq "APPROVED\n");
500 # If the program failed, collect the error message.
503 $err =~ s{ \n .* }{}xms;
505 die "$0: password strength checking failed without an error\n";
509 # Return the results.
510 return wantarray ? ($okay, $err, $status) : $okay;
513 # Read a Heimdal external password quality checking request from the provided
514 # file handle and return the principal (ignored for our application) and the
517 # The protocol expects the following data (without leading whitespace) on
518 # standard input, in precisely this order:
520 # principal: <principal>
521 # new-password: <password>
524 # There is one and only one space after the colon, and any subsequent spaces
525 # are part of the value (such as leading spaces in the password).
527 # $fh - File handle from which to read
529 # Returns: Scalar context: the password
530 # List context: a list of the password and the principal
531 # Throws: Text exception on any protocol violations or IO errors
532 sub read_change_data {
534 my @keys = qw(principal new-password);
537 # Read the data elements we expect. Verify that they come in the correct
538 # order and the correct format.
540 for my $key (@keys) {
541 my $line = readline($fh);
542 if (!defined($line)) {
543 die "$0: truncated input before $key: $!\n";
546 if ($line =~ s{ \A \Q$key\E : [ ] }{}xms) {
549 die "$0: unrecognized input line before $key\n";
553 # The final line of input must be a literal "end\n";
554 my $line = readline($fh);
555 if (!defined($line)) {
556 die "$0: truncated input before end: $!\n";
557 } elsif ($line ne "end\n") {
558 die "$0: unrecognized input line before end\n";
561 # Return the results.
562 my $password = $data{'new-password'};
563 my $principal = $data{principal};
564 return wantarray ? ($password, $principal) : $password;
567 ##############################################################################
569 ##############################################################################
571 # Always flush output.
574 # Clean up the script name for error reporting.
576 local $0 = basename($0);
578 # Parse the argument list.
579 my ($opt, $usage) = describe_options(
581 ['benchmark|b=f', 'Benchmark hash iterations for this target time'],
582 ['database|d=s', 'Path to the history database, overriding the default'],
583 ['help|h', 'Print usage message and exit'],
584 ['manual|man|m', 'Print full manual and exit'],
585 ['stats|S=s', 'Path to hash of length statistics'],
586 ['strength|s=s', 'Path to strength checking program to run'],
589 print {*STDOUT} $usage->text
590 or die "$0: cannot write to standard output: $!\n";
592 } elsif ($opt->manual) {
593 say {*STDOUT} 'Feeding myself to perldoc, please wait...'
594 or die "$0: cannot write to standard output: $!\n";
595 exec('perldoc', '-t', $fullpath);
597 my $database = $opt->database || $HISTORY_PATH;
598 my $stats_db = $opt->stats || $LENGTH_STATS_PATH;
600 # If asked to do benchmarking, ignore other arguments and just do that.
601 # Currently, we hard-code a 0.005-second granularity on our binary search.
602 if ($opt->benchmark) {
603 find_iteration_count($opt->benchmark, 0.005);
607 # Open syslog for result reporting.
608 openlog($0, 'pid', LOG_AUTH);
610 # Read the principal and password that we're supposed to check.
611 my ($password, $principal) = read_change_data(\*STDIN);
613 # Delegate to the external strength checking program.
614 my ($okay, $error, $status) = strength_check($principal, $password);
616 log_result($principal, 'rejected', $error);
621 # Drop privileges for the rest of the program.
622 drop_privileges($HISTORY_USER, $HISTORY_GROUP);
624 # Hash the password and check history. Exit if a hash is in history.
625 if (check_history($database, $principal, $password)) {
626 log_result($principal, 'rejected', $REJECT_MESSAGE);
627 warn "$REJECT_MESSAGE\n";
631 # The password is accepted. Record it, update the length counter, and return
633 log_result($principal, 'accepted');
634 write_history($database, $principal, $password);
635 say {*STDOUT} 'APPROVED'
636 or die "$0: cannot write to standard output: $!\n";
637 update_length_counts($stats_db, length($password));
642 ##############################################################################
644 ##############################################################################
647 heimdal-history heimdal-strength Heimdal -hm BerkeleyDB timestamps POSIX
648 whitespace API Allbery sublicense MERCHANTABILITY NONINFRINGEMENT syslog
649 pseudorandom JSON LDAP-compatible PBKDF2 SHA-256
653 heimdal-history - Password history via Heimdal external strength checking
657 B<heimdal-history> [B<-hm>] [B<-b> I<target-time>] [B<-d> I<database>]
658 [B<-S> I<length-stats-db>] [B<-s> I<strength-program>] [B<principal>]
662 B<heimdal-history> is an implementation of password history via the
663 Heimdal external password strength checking interface. It stores separate
664 history for each principal, hashed using Crypt::PBKDF2 with
665 randomly-generated salt. (The randomness is from a weak pseudorandom
666 number generator, not strongly random.)
668 Password history is stored in a BerkeleyDB DB_HASH file. The key is the
669 principal. The value is a JSON array of objects, each of which has two
670 keys. C<timestamp> contains the time when the history entry was added (in
671 POSIX seconds since UNIX epoch), and C<hash> contains the hash of a
672 previously-used password in the Crypt::PBKDF2 LDAP-compatible format.
673 Passwords are hashed using PBKDF2 (from PKCS#5) with SHA-256 as the
674 underlying hash function using a number of rounds configured in this
675 script. See L<Crypt::PBKDF2> for more information.
677 B<heimdal-history> also checks password strength before checking history.
678 It does so by invoking another program that also uses the Heimdal external
679 password strength checking interface. By default, it runs
680 B</usr/bin/heimdal-strength>. Only if that program approves the password
681 does it hash it and check history.
683 As with any implementation of the Heimdal external password strength
684 checking protocol, B<heimdal-history> expects, on standard input:
686 principal: <principal>
687 new-password: <password>
690 (with no leading whitespace). <principal> is the principal changing its
691 password (passed to the other password strength checking program but
692 otherwise unused here), and <password> is the new password. There must
693 be exactly one space after the colon. Any subsequent spaces are taken to
694 be part of the principal or password.
696 If invoked as root, B<heimdal-history> will run the external strength
697 checking program as user C<nobody> and group C<nogroup>, and will check
698 and write to the history database as user C<_history> and group
699 C<_history>. These users must exist on the system if it is run as root.
701 The result of each password check will be logged to syslog (priority
702 LOG_INFO, facility LOG_AUTH). Each log line will be a set of key/value
703 pairs in the format C<< I<key>=I<value> >>. The keys are:
709 The action performed (currently always C<check>).
713 The principal for which a password was checked.
717 An internal error message that did not stop the history check, but which
718 may indicate that something is wrong with the history database (such as
719 corrupted entries or invalid hashes). If this key is present, neither
720 C<result> nor C<reason> will be present. There will be a subsequent log
721 message from the same invocation giving the final result of the history
722 check (assuming B<heimdal-history> doesn't exit with a fatal error).
726 Either C<accepted> or C<rejected>.
730 If the password was rejected, the reason for the rejection.
734 The value will be surrounded with double quotes if it contains a double
735 quote or space. Any double quotes in the value will be doubled, so C<">
742 =item B<-b> I<target-time>, B<--benchmark>=I<target-time>
744 Do not do a password history check. Instead, benchmark the hash algorithm
745 with various possible iteration counts and find an iteration count that
746 results in I<target-time> seconds of computation time required to hash a
747 password (which should be a real number). A result will be considered
748 acceptable if it is within 0.005 seconds of the target time. The results
749 will be printed to standard output and then B<heimdal-history> will exit
752 =item B<-d> I<database>, B<--database>=I<database>
754 Use I<database> as the history database file instead of the default
755 (F</var/lib/heimdal-history/history.db>). Primarily used for testing,
756 since Heimdal won't pass this argument.
758 =item B<-h>, B<--help>
760 Print a short usage message and exit.
762 =item B<-m>, B<--manual>, B<--man>
764 Display this manual and exit.
766 =item B<-S> I<length-stats-db>, B<--stats>=I<length-stats-db>
768 Use I<length-stats-db> as the database file for password length statistics
769 instead of the default (F</var/lib/heimdal-history/lengths.db>).
770 Primarily used for testing, since Heimdal won't pass this argument.
772 =item B<-s> I<strength-program>, B<--strength>=I<strength-program>
774 Run I<strength-program> as the external strength-checking program instead
775 of the default (F</usr/bin/heimdal-strength>). Primarily used for
776 testing, since Heimdal won't pass this argument.
782 On approval of the password, B<heimdal-history> will print C<APPROVED> and
783 a newline to standard output and exit with status 0.
785 If the password is rejected by the strength checking program or if it (or
786 a version with a single character removed) matches one of the hashes stored
787 in the password history, B<heimdal-history> will print the reason for
788 rejection to standard error and exit with status 0.
790 On any internal error, B<heimdal-history> will print the error to standard
791 error and exit with a non-zero status.
797 =item F</usr/bin/heimdal-strength>
799 The default password strength checking program. This program must follow
800 the Heimdal external password strength checking API.
802 =item F</var/lib/heimdal-history/history.db>
804 The default database path. If B<heimdal-strength> is run as root, this
805 file needs to be readable and writable by user C<_history> and group
806 C<_history>. If it doesn't exist, it will be created with mode 0600.
808 =item F</var/lib/heimdal-history/history.db.lock>
810 The lock file used to synchronize access to the history database. As with
811 the history database, if B<heimdal-strength> is run as root, this file
812 needs to be readable and writable by user C<_history> and group
815 =item F</var/lib/heimdal-history/lengths.db>
817 The default length statistics path, which will be a BerkeleyDB DB_HASH
818 file of password lengths to counts of passwords with that length. If
819 B<heimdal-strength> is run as root, this file needs to be readable and
820 writable by user C<_history> and group C<_history>. If it doesn't exist,
821 it will be created with mode 0600.
823 =item F</var/lib/heimdal-history/lengths.db.lock>
825 The lock file used to synchronize access to the length statistics
826 database. As with the length statistics database, if B<heimdal-strength>
827 is run as root, this file needs to be readable and writable by user
828 C<_history> and group C<_history>.
834 Russ Allbery <eagle@eyrie.org>
836 =head1 COPYRIGHT AND LICENSE
838 Copyright 2013, 2014 The Board of Trustees of the Leland Stanford Junior
841 Permission is hereby granted, free of charge, to any person obtaining a
842 copy of this software and associated documentation files (the "Software"),
843 to deal in the Software without restriction, including without limitation
844 the rights to use, copy, modify, merge, publish, distribute, sublicense,
845 and/or sell copies of the Software, and to permit persons to whom the
846 Software is furnished to do so, subject to the following conditions:
848 The above copyright notice and this permission notice shall be included in
849 all copies or substantial portions of the Software.
851 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
852 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
853 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
854 THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
855 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
856 FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
857 DEALINGS IN THE SOFTWARE.
861 L<Crypt::PBKDF2>, L<heimdal-strength(1)>