Jon Portnoy (PAUSE Custodial Account) > App-bmkpasswd > App::bmkpasswd



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Module Version: 2.012002   Source  


App::bmkpasswd - bcrypt-capable mkpasswd(1) and exported bcrypt interface


  ## From Perl:

  use App::bmkpasswd -all;
  my $bcrypted = mkpasswd($passwd);
  say 'matched' if passwdcmp($passwd, $bcrypted);

  my $stronger = mkpasswd($passwd, 'bcrypt', 12);

  ## From a shell:

  bmkpasswd --help
  # Generate bcrypted passwords:

  # Defaults to work cost factor '08':
  bmkpasswd --workcost='06'

  # SHA requires Crypt::Passwd::XS or a recent libc:
  bmkpasswd --method='sha512'
  # Compare a hash:
  bmkpasswd --check=HASH

  # Check hash generation times:
  bmkpasswd --benchmark


App::bmkpasswd is a bcrypt-enabled mkpasswd implementation.

Helper functions are also exported for use in other applications; see "EXPORTED" -- however Crypt::Bcrypt::Easy (from this distribution) provides an easier bcrypt-specific programmatic interface for Perl programmers.

See bmkpasswd --help for command-line usage information.

Bcrypt leverages a work-cost factor allowing hash generation to become configurably slower as computers get faster, thereby impeding brute-force hash generation attempts. See for more on why you ought to be using bcrypt or similar "adaptive" techniques.

SHA-256 and SHA-512 are supported if available. SHA support requires either Crypt::Passwd::XS or a system crypt() that can handle SHA (such as glibc-2.7+ or modern FreeBSD builds).

This module uses Crypt::Eksblowfish::Bcrypt as a back-end.

Uses Bytes::Random::Secure::Tiny to generate random salts. Strongly-random salts can also be enabled; see "mkpasswd".


Crypt::Bcrypt::Easy provides an easier programmatic interface, but only generates bcrypt (although it can validate any supported type). If you would like to create crypted passwords using other methods, you can use the exported mkpasswd and passwdcmp functions:

  # Import selectively:
  use App::bmkpasswd 'mkpasswd', 'passwdcmp';
  # Or import all functions:
  use App::bmkpasswd -all;

This module uses Exporter::Tiny to export functions. This provides for flexible import options. See the Exporter::Tiny docs for details.


Compare a password against a hash.

  if ( passwdcmp($plaintext => $crypted) ) {
    ## Successful match
  } else {
    ## Failed match

passwdcmp will return the hash if it is a match; otherwise, undef is returned. (This is an API change in v2.7.1; prior versions return an empty list on failure.)

As of v2.10, a constant time comparison function is used to compare hashes.


  my $crypted = mkpasswd($passwd);
  my $crypted = mkpasswd($passwd, $type);
  my $crypted = mkpasswd($passwd, 'bcrypt', $cost);
  my $crypted = mkpasswd($passwd, $type, $cost, $strongsalt);

  my $crypted = mkpasswd( $passwd => 
      type    => $type,
      cost    => $cost,
      strong  => $strongsalt,
      saltgen => $saltgenerator,

Generate hashed passwords.

By default, generates a bcrypted passwd with work-cost 08:

  $bcrypted = mkpasswd($passwd);

A different work-cost can be specified for bcrypt passwds:

  $bcrypted = mkpasswd($passwd, 'bcrypt', '10');

SHA-256 and SHA-512 are supported, in which case the work-cost value is ignored:

  $crypted = mkpasswd($passwd, 'sha256');
  $crypted = mkpasswd($passwd, 'sha512');

If a fourth boolean-true argument is specified, a strongly-random salt is generated. This requires spare entropy, and will block if entropy-starved:

  $crypted = mkpasswd($passwd, 'bcrypt', '08', 'strong');
  $crypted = mkpasswd($passwd, 'sha512', 0, 'strong');

Options can be passed as a HASH, instead. This also lets you pass in a salt generator coderef:

  $crypted = mkpasswd( $passwd => +{
      type => 'bcrypt',
      cost => '10',
      strong  => 0,
      saltgen => $saltgenerator,

The salt generator is passed the type (one of: bcrypt, sha, md5) and the value of the strong option (default false).

  my $saltgenerator = sub {
    my ($type, $strongsalt) = @_;
    if ($type eq 'bcrypt') {
      # ...
    } elsif ($type eq 'sha') {
      # ...
    } else {
      die "Don't know how to create a salt for type '$type'!"

Most people want random salts, in which case the default salt generator should be fine.

See "mkpasswd_forked" if your application loads this module before forking or creating threads that generate passwords.


  my @available = mkpasswd_available;

  if ( mkpasswd_available('sha512') ) { ... }

Given no arguments, returns the list of available hash types.

Given a type (see "mkpasswd"), returns boolean true if the method is available. ('bcrypt' is always available.)


  # After a fork / new thread is created:

To retain secure salts after forking the process or creating a new thread, it's advisable to either only load this module after creating the new process or call mkpasswd_forked in the new process to reset the random seeds used by salt generators.

Added in v2.6.1.


Jon Portnoy <>

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