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package Mail::DKIM::ARC::Signer; use strict; use warnings; our $VERSION = '1.20230212'; # VERSION # ABSTRACT: generates a DKIM signature for a message # Copyright 2017 FastMail Pty Ltd. All Rights Reserved. # Bron Gondwana <brong@fastmailteam.com> # This program is free software; you can redistribute it and/or # modify it under the same terms as Perl itself. use Mail::DKIM::PrivateKey; use Mail::DKIM::ARC::MessageSignature; use Mail::DKIM::ARC::Seal; use Mail::AuthenticationResults::Parser; use Mail::AuthenticationResults::Header::AuthServID; use base 'Mail::DKIM::Common'; use Carp; # PROPERTIES # # public: # # $signer->{Algorithm} # identifies what algorithm to use when signing the message # default is "rsa-sha256" # # $signer->{Domain} # identifies what domain the message is signed for # # $signer->{SrvId} # identifies what authserv-id is in the A-R headers # # $signer->{KeyFile} # name of the file containing the private key used to sign # # $signer->{Policy} # a signing policy (of type Mail::DKIM::SigningPolicy) # # $signer->{Selector} # identifies name of the selector identifying the key # # $signer->{Key} # the loaded private key # # private: # # $signer->{algorithms} = [] # an array of algorithm objects... an algorithm object is created for # each signature being added to the message # # $signer->{result} # result of the signing policy: "signed" or "skipped" # # $signer->{details} # why we skipped this signature # # $signer->{signature} # the created signature (of type Mail::DKIM::Signature) sub init { my $self = shift; $self->SUPER::init; if ( defined $self->{KeyFile} ) { $self->{Key} ||= Mail::DKIM::PrivateKey->load( File => $self->{KeyFile} ); } unless ( $self->{'Algorithm'} ) { # use default algorithm $self->{'Algorithm'} = 'rsa-sha256'; } unless ( $self->{'Domain'} ) { # use default domain $self->{'Domain'} = 'example.org'; } unless ( $self->{'SrvId'} ) { # use default domain $self->{'SrvId'} = $self->{'Domain'}; } unless ( $self->{'Selector'} ) { # use default selector $self->{'Selector'} = 'unknown'; } $self->{result} = '?'; # better update this before we finish die 'Invalid signing algorithm' unless $self->{Algorithm} eq 'rsa-sha256'; # add ed25519 sometime die 'Need a valid chain value' unless $self->{Chain} and $self->{Chain} =~ m{^(pass|fail|none|ar)$}; } sub finish_header { my $self = shift; # add the AAR header my @aar; my @ams; my @as; my $ar; HEADER: foreach my $header ( @{ $self->{headers} } ) { $header =~ s/[\r\n]+$//; if ( $header =~ m/^Authentication-Results:/ ) { my ( $arval ) = $header =~ m/^Authentication-Results:[^;]*;[\t ]*(.*)/is; my $parsed; eval { $parsed= Mail::AuthenticationResults::Parser->new ->parse( $header ); 1 } || do { my $error = $@; warn "Authentication-Results Header parse error: $error\n$header"; next HEADER; }; my $ardom = $parsed->value->value; next unless "\L$ardom" eq $self->{SrvId}; # make sure it's our domain $arval =~ s/;?\s*$//; # ignore trailing semicolon and whitespace # preserve leading fold if there is one, otherwise set one leading space $arval =~ s/^\s*/ / unless ($arval =~ m/^\015\012/); if ($ar) { $ar .= ";$arval"; } else { $ar = "$ardom;$arval"; } # get chain value from A-R header $self->{Chain} = $1 if $self->{Chain} eq 'ar' and $arval =~ m{\barc=(none|pass|fail)}; } else { # parse ARC headers to make sure we have completeness if ( $header =~ m/^ARC-/ ) { if ( !$ar ) { $self->{result} = 'skipped'; $self->{details} = 'ARC header seen before Authentication-Results'; return; } if ( $self->{Chain} eq 'ar' ) { $self->{result} = 'skipped'; $self->{details} = 'No ARC result found in Authentication-Results'; return; } } if ( $header =~ m/^ARC-Seal:/ ) { my $seal = Mail::DKIM::ARC::Seal->parse($header); my $i = $seal->instance; if ( $as[$i] ) { $self->{result} = 'skipped'; $self->{details} = "Duplicate ARC-Seal $i"; return; } $as[$i] = $seal; } elsif ( $header =~ m/^ARC-Message-Signature:/ ) { my $sig = Mail::DKIM::ARC::MessageSignature->parse($header); my $i = $sig->instance; if ( $ams[$i] ) { $self->{result} = 'skipped'; $self->{details} = "Duplicate ARC-Message-Signature $i"; return; } $ams[$i] = $sig; } elsif ( $header =~ m/^ARC-Authentication-Results:\s*i=(\d+)/ ) { my $i = $1; if ( $aar[$i] ) { $self->{result} = 'skipped'; $self->{details} = "Duplicate ARC-Authentication-Results $i"; return; } $aar[$i] = $header; } } } unless ($ar) { $self->{result} = 'skipped'; $self->{details} = 'No authentication results seen'; return; } $self->{Chain} = 'none' if ($self->{Chain} eq 'ar'); if ( $#ams > $#as ) { $self->{result} = 'skipped'; $self->{details} = 'More message signatures than seals'; return; } if ( $#aar > $#as ) { $self->{result} = 'skipped'; $self->{details} = 'More authentication results than seals'; return; } foreach my $i ( 1 .. $#as ) { unless ( $as[$i] ) { $self->{result} = 'skipped'; $self->{details} = "Missing ARC-Seal $i"; return; } unless ( $ams[$i] ) { $self->{result} = 'skipped'; $self->{details} = "Missing Arc-Message-Signature $i"; return; } # don't care about authentication results, they are compulsary } $self->{_Instance} = @as || 1; # next instance value # first add the AAR header $self->{_AAR} = "ARC-Authentication-Results: i=$self->{_Instance}; $ar"; unshift @{ $self->{headers} }, $self->{_AAR}; # set up the signer for AMS $self->add_signature( Mail::DKIM::ARC::MessageSignature->new( Algorithm => $self->{Algorithm}, Headers => $self->headers, Instance => $self->{_Instance}, Method => 'relaxed/relaxed', Domain => $self->{Domain}, Selector => $self->{Selector}, Key => $self->{Key}, KeyFile => $self->{KeyFile}, ( $self->{Timestamp} ? ( Timestamp => $self->{Timestamp} ) : () ), ( $self->{Expiration} ? ( Expiration => $self->{Expiration} ) : () ), ) ); foreach my $algorithm ( @{ $self->{algorithms} } ) { # output header as received so far into canonicalization foreach my $header ( @{ $self->{headers} } ) { $algorithm->add_header($header); } $algorithm->finish_header( Headers => $self->{headers} ); } } sub finish_body { my $self = shift; if ( $self->{result} eq 'skipped' ) { # already failed $self->{_AS} = undef; return; } foreach my $algorithm ( @{ $self->{algorithms} } ) { # finished canonicalizing $algorithm->finish_body; # load the private key file if necessary my $signature = $algorithm->signature; my $key = $signature->{Key} || $signature->{KeyFile} || $self->{Key} || $self->{KeyFile}; if ( defined($key) && !ref($key) ) { $key = Mail::DKIM::PrivateKey->load( File => $key ); } $key or die "no key available to sign with\n"; # compute signature value my $signb64 = $algorithm->sign($key); $signature->data($signb64); # insert linebreaks in signature data, if desired $signature->prettify_safe(); $self->{_AMS} = $signature->as_string(); unshift @{ $self->{headers} }, $self->{_AMS}; } # reset the internal state $self->{signatures} = []; $self->{algorithms} = []; $self->add_signature( Mail::DKIM::ARC::Seal->new( Algorithm => $self->{Algorithm}, Chain => $self->{Chain}, Headers => $self->headers, Instance => $self->{_Instance}, Domain => $self->{Domain}, Selector => $self->{Selector}, Key => $self->{Key}, KeyFile => $self->{KeyFile}, ( $self->{Timestamp} ? ( Timestamp => $self->{Timestamp} ) : () ), ( $self->{Expiration} ? ( Expiration => $self->{Expiration} ) : () ), ) ); foreach my $algorithm ( @{ $self->{algorithms} } ) { # output header as received so far into canonicalization foreach my $header ( @{ $self->{headers} } ) { $algorithm->add_header($header); } # chain needed for seal canonicalization $algorithm->finish_header( Headers => $self->{headers}, Chain => $self->{Chain} ); # no body is required for ARC-Seal # finished canonicalizing $algorithm->finish_body; # load the private key file if necessary my $signature = $algorithm->signature; my $key = $signature->{Key} || $signature->{KeyFile} || $self->{Key} || $self->{KeyFile}; if ( defined($key) && !ref($key) ) { $key = Mail::DKIM::PrivateKey->load( File => $key ); } $key or die "no key available to sign ARC-Seal\n"; # compute signature value my $signb64 = $algorithm->sign($key); $signature->data($signb64); # insert linebreaks in signature data, if desired $signature->prettify_safe(); $self->{_AS} = $signature->as_string(); } $self->{result} = 'sealed'; } sub add_signature { my $self = shift; my $signature = shift; # create a canonicalization filter and algorithm my $algorithm_class = $signature->get_algorithm_class( $signature->algorithm ) or die 'unsupported algorithm ' . ( $signature->algorithm || '' ) . "\n"; my $algorithm = $algorithm_class->new( Signature => $signature, Debug_Canonicalization => $self->{Debug_Canonicalization}, ); push @{ $self->{algorithms} }, $algorithm; return; } sub algorithm { my $self = shift; if ( @_ == 1 ) { $self->{Algorithm} = shift; } return $self->{Algorithm}; } sub domain { my $self = shift; if ( @_ == 1 ) { $self->{Domain} = shift; } return $self->{Domain}; } # these are headers that "should" be included in the signature, # according to the DKIM spec. my @DEFAULT_HEADERS = qw(From Sender Reply-To Subject Date Message-ID To Cc MIME-Version Content-Type Content-Transfer-Encoding Content-ID Content-Description Resent-Date Resent-From Resent-Sender Resent-To Resent-cc Resent-Message-ID In-Reply-To References List-Id List-Help List-Unsubscribe List-Subscribe List-Post List-Owner List-Archive); sub process_headers_hash { my $self = shift; my @headers; # these are the header fields we found in the message we're signing my @found_headers = @{ $self->{header_field_names} }; # Convert all keys to lower case foreach my $header ( keys %{ $self->{'ExtendedHeaders'} } ) { next if $header eq lc $header; if ( exists $self->{'ExtendedHeaders'}->{ lc $header } ) { # Merge my $first = $self->{'ExtendedHeaders'}->{ lc $header }; my $second = $self->{'ExtendedHeaders'}->{$header}; if ( $first eq '+' || $second eq '+' ) { $self->{'ExtendedHeaders'}->{ lc $header } = '+'; } elsif ( $first eq '*' || $second eq '*' ) { $self->{'ExtendedHeaders'}->{ lc $header } = '*'; } else { $self->{'ExtendedHeaders'}->{ lc $header } = $first + $second; } } else { # Rename $self->{'ExtendedHeaders'}->{ lc $header } = $self->{'ExtendedHeaders'}->{$header}; } delete $self->{'ExtendedHeaders'}->{$header}; } # Add the default headers if ( !$self->{'NoDefaultHeaders'} ) { foreach my $default (@DEFAULT_HEADERS) { if ( !exists $self->{'ExtendedHeaders'}->{ lc $default } ) { $self->{'ExtendedHeaders'}->{ lc $default } = '*'; } } } # Build a count of found headers my $header_counts = {}; foreach my $header (@found_headers) { if ( !exists $header_counts->{ lc $header } ) { $header_counts->{ lc $header } = 1; } else { $header_counts->{ lc $header } = $header_counts->{ lc $header } + 1; } } foreach my $header ( sort keys %{ $self->{'ExtendedHeaders'} } ) { my $want_count = $self->{'ExtendedHeaders'}->{$header}; my $have_count = $header_counts->{ lc $header } || 0; my $add_count = 0; if ( $want_count eq '+' ) { $add_count = $have_count + 1; } elsif ( $want_count eq '*' ) { $add_count = $have_count; } else { if ( $want_count > $have_count ) { $add_count = $have_count; } else { $add_count = $want_count; } } for ( 1 .. $add_count ) { push @headers, $header; } } return join( ':', @headers ); } sub extended_headers { my $self = shift; $self->{'ExtendedHeaders'} = shift; return; } sub headers { my $self = shift; croak 'unexpected argument' if @_; if ( exists $self->{'ExtendedHeaders'} ) { return $self->process_headers_hash(); } # these are the header fields we found in the message we're signing my @found_headers = @{ $self->{header_field_names} }; # these are the headers we actually want to sign my @wanted_headers; if ( !$self->{'NoDefaultHeaders'} ) { @wanted_headers = @DEFAULT_HEADERS; } if ( $self->{Headers} ) { push @wanted_headers, split /:/, $self->{Headers}; } my @headers = grep { my $a = $_; scalar grep { lc($a) eq lc($_) } @wanted_headers } @found_headers; return join( ':', @headers ); } # return nonzero if this is header we should sign sub want_header { my $self = shift; my ($header_name) = @_; #TODO- provide a way for user to specify which headers to sign return scalar grep { lc($_) eq lc($header_name) } @DEFAULT_HEADERS; } sub key { my $self = shift; if (@_) { $self->{Key} = shift; $self->{KeyFile} = undef; } return $self->{Key}; } sub key_file { my $self = shift; if (@_) { $self->{Key} = undef; $self->{KeyFile} = shift; } return $self->{KeyFile}; } sub selector { my $self = shift; if ( @_ == 1 ) { $self->{Selector} = shift; } return $self->{Selector}; } sub signatures { my $self = shift; croak 'no arguments allowed' if @_; return map { $_->signature } @{ $self->{algorithms} }; } sub as_string { my $self = shift; return '' unless $self->{_AS}; # skipped, no signature return join( "\015\012", $self->{_AS}, $self->{_AMS}, $self->{_AAR}, '' ); } sub as_strings { my $self = shift; return ( $self->{_AS}, $self->{_AMS}, $self->{_AAR} ); } 1; __END__ =pod =encoding UTF-8 =head1 NAME Mail::DKIM::ARC::Signer - generates a DKIM signature for a message =head1 VERSION version 1.20230212 =head1 SYNOPSIS use Mail::DKIM::ARC::Signer; use Mail::DKIM::TextWrap; #recommended # create a signer object my $signer = Mail::DKIM::ARC::Signer->new( Algorithm => 'rsa-sha256', Chain => 'none', # or pass|fail|ar Domain => 'example.org', SrvId => 'example.org', Selector => 'selector1', KeyFile => 'private.key', Headers => 'x-header:x-header2', ); # read an email from a file handle $signer->load(*STDIN); # NOTE: any email being ARC signed must have an Authentication-Results # header so that the ARC seal can cover those results copied into # an ARC-Authentication-Results header. # or read an email and pass it into the signer, one line at a time while (<STDIN>) { # remove local line terminators chomp; s/\015$//; # use SMTP line terminators $signer->PRINT("$_\015\012"); } $signer->CLOSE; die 'Failed' $signer->result_detail() unless $signer->result() eq 'sealed'; # Get all the signature headers to prepend to the message # ARC-Seal, ARC-Message-Signature and ARC-Authentication-Results # in that order. print $signer->as_string; =head1 DESCRIPTION This class is the part of L<Mail::DKIM> responsible for generating ARC Seals for a given message. You create an object of this class, specifying the parameters for the ARC-Message-Signature you wish to create. You also need to pass the 'Chain' value (pass or fail) from validation of the previous ARC-Seals on the message. Next, you feed it the entire message using L</"PRINT()">, completing with L</"CLOSE()">. Finally, use the L</"as_string()"> method to get the new ARC headers. Note: you can only seal a message which has already had an Authentication-Results header added, either by using L</"PRINT()"> to pre-feed it into this module, or by adding a message which has already been authenticated by your inbound scanning mechanisms. It is not necessary to ARC-Seal a message which already has DKIM signatures if you are not modifying the message and hence breaking the existing DKIM-Signature or top ARC-Message-Signature on the email. =head2 Pretty Signatures L<Mail::DKIM> includes a signature-wrapping module (which inserts linebreaks into the generated signature so that it looks nicer in the resulting message. To enable this module, simply call use Mail::DKIM::TextWrap; in your program before generating the signature. =head1 CONSTRUCTOR =head2 new() Construct an object-oriented signer. # create a signer using the default policy my $signer = Mail::DKIM::ARC::Signer->new( Algorithm => 'rsa-sha256', Chain => 'none', # or pass|fail|ar Domain => 'example.org', SrvId => 'example.org', Selector => 'selector1', KeyFile => 'private.key', Headers => 'x-header:x-header2', ); =over =item Key rather than using C<KeyFile>, use C<Key> to use an already-loaded L<Mail::DKIM::PrivateKey> object. =item Chain The cv= value for the Arc-Seal header. "ar" means to copy it from an Authentication-Results header, or use none if there isn't one. =item SrvId The authserv-id in the Authentication-Results headers, defaults to Domain. =item Headers A colon separated list of headers to sign, this is added to the list of default headers as shown in in the DKIM specification. For each specified header all headers of that type which are present in the message will be signed, but we will not oversign or sign headers which are not present. If you require greater control over signed headers please use the extended_headers() method instead. The list of headers signed by default is as follows From Sender Reply-To Subject Date Message-ID To Cc MIME-Version Content-Type Content-Transfer-Encoding Content-ID Content-Description Resent-Date Resent-From Resent-Sender Resent-To Resent-cc Resent-Message-ID In-Reply-To References List-Id List-Help List-Unsubscribe List-Subscribe List-Post List-Owner List-Archive =back =head1 METHODS =head2 PRINT() Feed part of the message to the signer. $signer->PRINT("a line of the message\015\012"); Feeds content of the message being signed into the signer. The API is designed this way so that the entire message does NOT need to be read into memory at once. Please note that although the PRINT() method expects you to use SMTP-style line termination characters, you should NOT use the SMTP-style dot-stuffing technique described in RFC 2821 section 4.5.2. Nor should you use a <CR><LF>.<CR><LF> sequence to terminate the message. =head2 CLOSE() Call this when finished feeding in the message. $signer->CLOSE; This method finishes the canonicalization process, computes a hash, and generates a signature. =head2 extended_headers() This method overrides the headers to be signed and allows more control than is possible with the Headers property in the constructor. The method expects a HashRef to be passed in. The Keys are the headers to sign, and the values are either the number of headers of that type to sign, or the special values '*' and '+'. * will sign ALL headers of that type present in the message. + will sign ALL + 1 headers of that type present in the message to prevent additional headers being added. You may override any of the default headers by including them in the hashref, and disable them by giving them a 0 value. Keys are case insensitive with the values being added upto the highest value. Headers => { 'X-test' => '*', 'x-test' => '1', 'Subject' => '+', 'Sender' => 0, }, =head2 add_signature() Used by signer policy to create a new signature. $signer->add_signature(new Mail::DKIM::Signature(...)); Signer policies can use this method to specify complete parameters for the signature to add, including what type of signature. For more information, see L<Mail::DKIM::SignerPolicy>. =head2 algorithm() Get or set the selected algorithm. $alg = $signer->algorithm; $signer->algorithm('rsa-sha256'); =head2 domain() Get or set the selected domain. $alg = $signer->domain; $signer->domain('example.org'); =head2 load() Load the entire message from a file handle. $signer->load($file_handle); Reads a complete message from the designated file handle, feeding it into the signer. The message must use <CRLF> line terminators (same as the SMTP protocol). =head2 headers() Determine which headers to put in signature. my $headers = $signer->headers; This is a string containing the names of the header fields that will be signed, separated by colons. =head2 key() Get or set the private key object. my $key = $signer->key; $signer->key(Mail::DKIM::PrivateKey->load(File => 'private.key')); The key object can be any object that implements the L<sign_digest() method|Mail::DKIM::PrivateKey/"sign_digest()">. (Providing your own object can be useful if your actual keys are stored out-of-process.) If you use this method to specify a private key, do not use L</"key_file()">. =head2 key_file() Get or set the filename containing the private key. my $filename = $signer->key_file; $signer->key_file('private.key'); If you use this method to specify a private key file, do not use L</"key()">. =head2 message_originator() Access the "From" header. my $address = $signer->message_originator; Returns the "originator address" found in the message, as a L<Mail::Address> object. This is typically the (first) name and email address found in the From: header. If there is no From: header, then an empty L<Mail::Address> object is returned. To get just the email address part, do: my $email = $signer->message_originator->address; See also L</"message_sender()">. =head2 message_sender() Access the "From" or "Sender" header. my $address = $dkim->message_sender; Returns the "sender" found in the message, as a L<Mail::Address> object. This is typically the (first) name and email address found in the Sender: header. If there is no Sender: header, it is the first name and email address in the From: header. If neither header is present, then an empty L<Mail::Address> object is returned. To get just the email address part, do: my $email = $dkim->message_sender->address; The "sender" is the mailbox of the agent responsible for the actual transmission of the message. For example, if a secretary were to send a message for another person, the "sender" would be the secretary and the "originator" would be the actual author. =head2 selector() Get or set the current key selector. $alg = $dkim->selector; $dkim->selector('alpha'); =head2 signatures() Access list of generated signature objects. my @signatures = $dkim->signatures; Returns all generated signatures, as a list. =head2 as_string() Returns the new ARC headers my $pre_headers = $signer->as_string(); The headers are separated by \015\012 (SMTP line separator) including a trailing separator, so can be directly injected in front of the raw message. =head2 as_strings() Returns the new ARC headers my @pre_headers = $signer->as_string(); The headers are returned as a list so you can add whatever line ending your local MTA prefers. =head1 AUTHORS =over 4 =item * Jason Long <jason@long.name> =item * Marc Bradshaw <marc@marcbradshaw.net> =item * Bron Gondwana <brong@fastmailteam.com> (ARC) =back =head1 THANKS Work on ensuring that this module passes the ARC test suite was generously sponsored by Valimail (https://www.valimail.com/) =head1 COPYRIGHT AND LICENSE =over 4 =item * Copyright (C) 2013 by Messiah College =item * Copyright (C) 2010 by Jason Long =item * Copyright (C) 2017 by Standcore LLC =item * Copyright (C) 2020 by FastMail Pty Ltd =back This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.6 or, at your option, any later version of Perl 5 you may have available. =cut