PGP::Sign version 0.20

(Create and verify detached PGP signatures for data)

Copyright 1997, 1998, 1999, 2000, 2002, 2004, 2007 Russ Allbery <rra@cpan.org>. 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@cpan.org. :)

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!

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