NAME
    Module::Signature - Module signature file manipulation

SYNOPSIS
    As a shell command:

        % cpansign              # verify an existing SIGNATURE, or
                                # make a new one if none exists

        % cpansign sign         # make signature; overwrites existing one
        % cpansign -s           # same thing

        % cpansign verify       # verify a signature
        % cpansign -v           # same thing
        % cpansign -v --skip    # ignore files in MANIFEST.SKIP

        % cpansign help         # display this documentation
        % cpansign -h           # same thing

    In programs:

        use Module::Signature qw(sign verify SIGNATURE_OK);
        sign();
        sign(overwrite => 1);       # overwrites without asking

        # see the CONSTANTS section below
        (verify() == SIGNATURE_OK) or die "failed!";

DESCRIPTION
    Module::Signature adds cryptographic authentications to CPAN
    distributions, via the special SIGNATURE file.

    If you are a module user, all you have to do is to remember to run
    "cpansign -v" (or just "cpansign") before issuing "perl Makefile.PL" or
    "perl Build.PL"; that will ensure the distribution has not been tampered
    with.

    Module authors can easily add the SIGNATURE file to the distribution
    tarball; see "NOTES" below for how to do it as part of "make dist".

    If you *really* want to sign a distribution manually, simply add
    "SIGNATURE" to MANIFEST, then type "cpansign -s" immediately before
    "make dist". Be sure to delete the SIGNATURE file afterwards.

    Please also see "NOTES" about MANIFEST.SKIP issues, especially if you
    are using Module::Build or writing your own MANIFEST.SKIP.

    Signatures made with Module::Signature prior to version 0.82 used the
    SHA1 algorithm by default. SHA1 is now considered broken, and therefore
    module authors are strongly encouraged to regenerate their SIGNATURE
    files. Users verifying old SHA1 signature files will receive a warning.

VARIABLES
    No package variables are exported by default.

    $Verbose
        If true, Module::Signature will give information during processing
        including gpg output. If false, Module::Signature will be as quiet
        as possible as long as everything is working ok. Defaults to false.

    $SIGNATURE
        The filename for a distribution's signature file. Defaults to
        "SIGNATURE".

    $AUTHOR
        The key ID used for signature. If empty/null/0, "gpg"'s configured
        default ID, or the most recently added key within the secret keyring
        for "Crypt::OpenPGP", will be used for the signature.

    $KeyServer
        The OpenPGP key server for fetching the author's public key
        (currently only implemented on "gpg", not "Crypt::OpenPGP"). May be
        set to a false value to prevent this module from fetching public
        keys.

    $KeyServerPort
        The OpenPGP key server port, defaults to 11371.

    $Timeout
        Maximum time to wait to try to establish a link to the key server.
        Defaults to 3.

    $AutoKeyRetrieve
        Whether to automatically fetch unknown keys from the key server.
        Defaults to 1.

    $Cipher
        The default cipher used by the "Digest" module to make signature
        files. Defaults to "SHA256", but may be changed to other ciphers via
        the "MODULE_SIGNATURE_CIPHER" environment variable if the SHA256
        cipher is undesirable for the user.

        The cipher specified in the SIGNATURE file's first entry will be
        used to validate its integrity. For "SHA256", the user needs to have
        any one of these modules installed: Digest::SHA, Digest::SHA256, or
        Digest::SHA::PurePerl.

    $Preamble
        The explanatory text written to newly generated SIGNATURE files
        before the actual entries.

ENVIRONMENT
    Module::Signature honors these environment variables:

    MODULE_SIGNATURE_AUTHOR
        Works like $AUTHOR.

    MODULE_SIGNATURE_CIPHER
        Works like $Cipher.

    MODULE_SIGNATURE_VERBOSE
        Works like $Verbose.

    MODULE_SIGNATURE_KEYSERVER
        Works like $KeyServer.

    MODULE_SIGNATURE_KEYSERVERPORT
        Works like $KeyServerPort.

    MODULE_SIGNATURE_TIMEOUT
        Works like $Timeout.

CONSTANTS
    These constants are not exported by default.

    CANNOT_VERIFY (0E0)
        Cannot verify the OpenPGP signature, maybe due to the lack of a
        network connection to the key server, or if neither gnupg nor
        Crypt::OpenPGP exists on the system.

    SIGNATURE_OK (0)
        Signature successfully verified.

    SIGNATURE_MISSING (-1)
        The SIGNATURE file does not exist.

    SIGNATURE_MALFORMED (-2)
        The signature file does not contains a valid OpenPGP message.

    SIGNATURE_BAD (-3)
        Invalid signature detected -- it might have been tampered with.

    SIGNATURE_MISMATCH (-4)
        The signature is valid, but files in the distribution have changed
        since its creation.

    MANIFEST_MISMATCH (-5)
        There are extra files in the current directory not specified by the
        MANIFEST file.

    CIPHER_UNKNOWN (-6)
        The cipher used by the signature file is not recognized by the
        "Digest" and "Digest::*" modules.

NOTES
  Signing your module as part of "make dist"
    The easiest way is to use Module::Install:

        sign;       # put this before "WriteAll"
        WriteAll;

    For ExtUtils::MakeMaker (version 6.18 or above), you may do this:

        WriteMakefile(
            (MM->can('signature_target') ? (SIGN => 1) : ()),
            # ... original arguments ...
        );

    Users of Module::Build may do this:

        Module::Build->new(
            (sign => 1),
            # ... original arguments ...
        )->create_build_script;

  MANIFEST.SKIP Considerations
    (The following section is lifted from Iain Truskett's Test::Signature
    module, under the Perl license. Thanks, Iain!)

    It is imperative that your MANIFEST and MANIFEST.SKIP files be accurate
    and complete. If you are using "ExtUtils::MakeMaker" and you do not have
    a MANIFEST.SKIP file, then don't worry about the rest of this. If you do
    have a MANIFEST.SKIP file, or you use "Module::Build", you must read
    this.

    Since the test is run at "make test" time, the distribution has been
    made. Thus your MANIFEST.SKIP file should have the entries listed below.

    If you're using "ExtUtils::MakeMaker", you should have, at least:

        #defaults
        ^Makefile$
        ^blib/
        ^pm_to_blib
        ^blibdirs

    These entries are part of the default set provided by
    "ExtUtils::Manifest", which is ignored if you provide your own
    MANIFEST.SKIP file.

    If you are using "Module::Build", you should have two extra entries:

        ^Build$
        ^_build/

    If you don't have the correct entries, "Module::Signature" will complain
    that you have:

        ==> MISMATCHED content between MANIFEST and distribution files! <==

    You should note this during normal development testing anyway.

  Testing signatures
    You may add this code as t/0-signature.t in your distribution tree:

        #!/usr/bin/perl

        use strict;
        print "1..1\n";

        if (!$ENV{TEST_SIGNATURE}) {
            print "ok 1 # skip Set the environment variable",
                        " TEST_SIGNATURE to enable this test\n";
        }
        elsif (!-s 'SIGNATURE') {
            print "ok 1 # skip No signature file found\n";
        }
        elsif (!eval { require Module::Signature; 1 }) {
            print "ok 1 # skip ",
                    "Next time around, consider install Module::Signature, ",
                    "so you can verify the integrity of this distribution.\n";
        }
        elsif (!eval { require Socket; Socket::inet_aton('keyserver.ubuntu.com') }) {
            print "ok 1 # skip ",
                    "Cannot connect to the keyserver\n";
        }
        else {
            (Module::Signature::verify() == Module::Signature::SIGNATURE_OK())
                or print "not ";
            print "ok 1 # Valid signature\n";
        }

        __END__

    If you are already using Test::More for testing, a more straightforward
    version of t/0-signature.t can be found in the Module::Signature
    distribution.

    Note that "MANIFEST.SKIP" is considered by default only when
    $ENV{TEST_SIGNATURE} is set to a true value.

    Also, if you prefer a more full-fledged testing package, and are willing
    to inflict the dependency of Module::Build on your users, Iain
    Truskett's Test::Signature might be a better choice.

SEE ALSO
    Digest, Digest::SHA, Digest::SHA::PurePerl

    ExtUtils::Manifest, Crypt::OpenPGP, Test::Signature

    Module::Install, ExtUtils::MakeMaker, Module::Build

    Dist::Zilla::Plugin::Signature

AUTHORS
    Audrey Tang <cpan@audreyt.org>

LICENSE
    This work is under a CC0 1.0 Universal License, although a portion of
    the documentation (as detailed above) is under the Perl license.

    To the extent possible under law, 唐鳳 has waived all copyright and
    related or neighboring rights to Module-Signature.

    This work is published from Taiwan.

    <http://creativecommons.org/publicdomain/zero/1.0>