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Module::Signature - Module signature file manipulation


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(overwrite => 1);       # overwrites without asking

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


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.


No package variables are exported by default.


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.


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


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.


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.


The OpenPGP key server port, defaults to 11371.


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


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


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.


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


Module::Signature honors these environment variables:


Works like $AUTHOR.


Works like $Cipher.


Works like $Verbose.


Works like $KeyServer.


Works like $KeyServerPort.


Works like $Timeout.


These constants are not exported by default.


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 successfully verified.


The SIGNATURE file does not exist.


The signature file does not contains a valid OpenPGP message.


Invalid signature detected -- it might have been tampered with.


The signature is valid, but files in the distribution have changed since its creation.


There are extra files in the current directory not specified by the MANIFEST file.


The cipher used by the signature file is not recognized by the Digest and Digest::* modules.


Signing your module as part of make dist

The easiest way is to use Module::Install:

    sign;       # put this before "WriteAll"

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

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

Users of Module::Build may do this:

        (sign => 1),
        # ... original arguments ...

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:


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:


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:


    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('') }) {
        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";


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.


Digest, Digest::SHA, Digest::SHA::PurePerl

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

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



Audrey Tang <>


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.