PGP::Sign version 0.20
           (Create and verify detached PGP signatures for data)

  Copyright 1997, 1998, 1999, 2000, 2002, 2004, 2007 Russ Allbery
  <rra@stanford.edu>.  This program is free software; you may redistribute
  it and/or modify it under the same terms as Perl itself.

INTRODUCTION

  One important thing to clear up right away:  This is not a general PGP
  module.

  For wonderful general PGP modules that will encrypt, decrypt, manage key
  rings, slice, dice, fold, spindle, and mutilate your data, see the PGP
  by-module directory at your local CPAN mirror; hopefully there will be
  one there.  This module sprung out of a need to do one thing and one
  thing only, do it securely, and do it well.  This module creates and
  checks detached signatures for data.  That's it.  If you want to do
  anything else that PGP lets you do, look elsewhere.

  Currently this module only works with text data.  Support for binary
  data is high on the list of features I want to add.

  The original purpose of this module was to factor out common code in a
  News::Article class written by Andrew Gierth that did PGPMoose
  signatures and signed control messages.  It should now be possible to
  reimplement PGPMoose, signcontrol, and pgpverify using this module, and
  the second and parts of the first have already been done.

  So much for the "one thing only" part.  For the "do it securely" part,
  this module uses a pipe to pass the secret key password to PGP, rather
  than a command line flag or an environment variable as seen in other
  modules.  Both of those are subject to snooping by other users; this
  approach isn't.

  For the "do it well" part, the interface to this module takes every form
  of data known to man.  Scalars and arrays are no problem, of course, but
  if you give it a reference to an array, it'll walk the array to avoid
  making a copy of a potentially large data structure.  You can also give
  it an open file (in the form of a glob, a reference to a glob, a
  FileHandle object, an IO::Handle object, or anything derived from
  either) and it'll walk that too.  Or you can give it a reference to a
  scalar if you really want to and it's cool with that.  Or, if you want
  to get really exciting, you can give it a reference to a sub and it'll
  call the sub repeatedly to get more data until the sub returns undef.
  Perfect for walking some complex data structure you don't want to make
  an internal copy of.  And if there's any other interesting data
  structure you want to throw at it, tell me about it, and the next
  version will probably support that too.

  This module supports a wide variety of different versions of PGP, from
  PGP 2.6.2 to PGP 5.0 to PGP 6.5 to the new (and very nice) GnuPG.
  Different implementations of PGP are capable (and not capable) of
  creating and checking various types of signatures; obviously, what this
  module can do is limited by what versions of PGP you have installed.

  See the documentation for all the gory details, which really aren't that
  gory.  At least yet.

REQUIREMENTS

  This module requires a version of PGP that supports PGPPASSFD or some
  other mechanism for handing the passphrase over in a pipe.  2.6.2,
  2.6.3i, 5.0, 6.5, and GnuPG all do.  I can't personally vouch for any
  other version, but I believe ViaCrypt PGP 4.0 may also work (since it's
  largely based on 2.6.2).  This module also requires an operating system
  that's capable of coping with pipes, forking, and passing file
  descriptors through an exec().  If your operating system can't, that's
  considered by this module author to be a bug in your operating system
  and not in this module.

  I've personally tested or received reports of clean tests of this module
  with the following versions of PGP:

      PGP 2.6.2 (US version)
      PGP 2.6.2i
      PGP 5.0 (US Linux freeware version)
      PGP 6.5.2 (US Solaris freeware version)
      GnuPG 0.9.2 (Linux and Solaris)
      GnuPG 1.0.1 (Solaris)
      GnuPG 1.0.6 (Solaris)
      GnuPG 1.2.1 (Linux)
      GnuPG 1.2.2 (FreeBSD and OpenBSD)
      GnuPG 1.2.4 (Linux)
      GnuPG 1.4.6 (Linux)

  If you successfully use this module with another significant version of
  PGP not listed above, please let me know.

  This module requires no other modules besides IPC::Open3 and FileHandle,
  both of which are part of Perl core and have been for some time.  It
  should work with Perl 5.003 or later, although I personally have only
  tested it with Perl 5.004_04, 5.005_03, 5.6.1, 5.8.0, 5.8.4, and 5.8.8.

INSTALLATION

  Follow the standard installation procedure for Perl modules, which is to
  type the following commands:

      perl Makefile.PL
      make
      make test
      make install

  You'll probably need to do the last as root unless you're installing in
  your own private modules directory.

  In order for make test to succeed if you're using GnuPG and egd (the
  entropy daemon), you may have to make a symlink from data/entropy to the
  entropy socket in your ~/.gnupg directory.

  When you run make, you will be prompted for the path to the program to
  create signatures and the program to verify signatures.  PGP::Sign will
  try to guess at what you may want to use, preferring GnuPG and then PGP
  5.0.  For GnuPG, PGP 2.6, or PGP 6.5, both paths should point to the
  same program; for PGP 5.0, pgps is the program that generates signatures
  and pgpv is the program that verifies them.  Don't set the signing
  program and the verifying program to mutually incompatible things, or
  you'll get strange results.

  You will also be prompted for what PGP style to default to, since each
  PGP implementation works slightly differently.  This has to be one of
  the following:  "PGP2" for PGP 2.6 workalikes, "PGP5" for PGP 5.0 and
  workalikes, "PGP6" for PGP 6.5 and workalikes, or "GPG" for GnuPG.
  Again, PGP::Sign will try to guess from the name of the binaries you
  chose (and distinguish between PGP2 and PGP6 based on the output of the
  program when run without any arguments).

  If you have multiple versions of PGP installed on your system, you still
  have to pick one to be the default.  You'll be able to switch between
  PGP programs and PGP styles at runtime; see the PGP::Sign documentation
  for details.

  If you want to avoid the prompt for the path to PGP, you can, instead of
  the first line, type:

      perl Makefile.PL PGP=/path/to/pgp

  and then /path/to/pgp will be used as the path to PGP (both signing and
  verification) and you won't be prompted.  When invoked this way,
  Makefile.PL will attempt to figure out what PGP style you're using from
  the name of the binaries.  You can set it specifically with something
  like:

      perl Makefile.PL PGP=/usr/local/bin/gpg PGPSTYLE=GPG

  if you need to.  If the signing program and verifying program are
  different, set PGPS and PGPV instead of just PGP.  For example:

      perl Makefile.PL PGPS=/usr/local/bin/pgps PGPV=/usr/local/bin/pgpv

  If you want to install PGP::Sign in somewhere other than the default
  installation location, you can set PREFIX or LIB on the Makefile.PL
  command line.  See the ExtUtils::MakeMaker documentation for more
  details.

TESTING

  There is a small test suite that uses the files in data to make sure
  that signing and checking of signatures work.  This test suite uses the
  key rings and data in the data subdirectory of the distribution, and
  should work correctly under any of the supported versions of PGP.

  To run the test suite, type:

      make test

  after running make.  Regardless of your PGP style, at least one test
  will be skipped, since PGP::Sign knows how to test RSA signatures (PGP
  2.6, PGP 5.0, and PGP 6.5), DSS version three signatures (PGP 5.0, PGP
  6.5, and GnuPG), and DSS version four signatures (GnuPG only), and no
  one PGP implementation can handle all three (unless your GnuPG
  installation includes RSA support).

  For some reason, the test suite fails the first time it's run with PGP
  6.5 (at least on Solaris), giving error messages about not having enough
  random bits, and then succeeds the second time.  I consider this to be a
  bug in PGP 6.5, as no other version of PGP has this problem.

  Note that different PGP implementations return different things and
  therefore the test suite looks for different things depending on what
  your PGP style is set to.  See the PGP::Sign documentation for an
  extended discussion of issues related to trailing whitespace, and see
  the comments in test.pl for information on exactly what's being tested.

  More tests are welcome, particularly if you find a bug or if they test
  some major functionality of this module not currently covered.

THANKS

  To Andrew Gierth for the inspiration and motivation to write this and
  the reminder that PGPPASSFD existed, for being one of the two people who
  caught the mistake I made with $? and open3(), and for pointing out a
  missing waitpid() in pgp_verify() that was causing zombies.

  To Jon Ribbens for pointing out that $? isn't guaranteed to contain the
  exit status of something called from open3() unless you do a waitpid()
  for it first.

  To Andrew Ford for adding PGPPATH support and adding a test suite and
  code in Makefile.PL to search for an installed version of PGP.

  To Todd Underwood for the impetus to get this module working under GnuPG
  and PGP 5.0, and to he and Monte Mitzelfelt for the initial GnuPG
  implementation that I based mine on.

  To Lupe Christoph for pointing out that Perl 5.005_03 sets close-on-exec
  on file handles created by pipe, requiring an fcntl() call in PGP::Sign
  to unset that.

  To J. Porter Clark for information about the socket needed for GnuPG
  with egd support.

  To Marco d'Itri for example code on how to use the GnuPG --status-fd
  support, so that parsing of the human-readable output of GnuPG isn't
  needed, and to Autrijus Tang for reminding me that I'd not yet pulled
  that code over from pgpverify.

  To David Lawrence and Greg Rose for signcontrol and PGPMoose
  respectively, the motivating applications.

  To Phil Zimmermann, because Phil should be listed in the thank you list
  for anything related to PGP, given that he wrote it and went through
  legal hell to make sure we still had it available.

  To Werner Koch for GnuPG, which is much nicer than any other PGP
  implementation I've worked with and is free to boot, and for pointing me
  at the right sections of RFC 2440 to explain the OpenPGP standard on
  whitespace munging in text signatures.

CONTACTING ME AND CONTRIBUTIONS

  Send any comments, bug reports, feature requests, flames, thank yous,
  offers of vast quantities of money, lutefisk, and large green Martian
  dogs named Ralf to rra@stanford.edu.  :)

  Please allow at least a month for me to respond to mail regarding this
  module.  I get at *least* 1,000 mail messages a day, and I'm afraid this
  module is something that I only get a chance to work on once every few
  months.  I do intend to continue to maintain it, however, and I will get
  back to you eventually.

  Contributions are welcome!  I will not have enough time to add
  everything I want to add to this module, but I tend to be sparked into
  bursts of creativity and programming energy when sent new ideas or
  patches, even partial ones.  If you're interested in contributing,
  please read TODO first.

  Enjoy!