Provided by: libmail-dkim-perl_1.20230212-1ubuntu1_all 
NAME
Mail::DKIM::Signature - represents a DKIM-Signature header
VERSION
version 1.20230212
CONSTRUCTORS
new() - create a new signature from parameters
my $signature = Mail::DKIM::Signature->new(
[ Algorithm => 'rsa-sha1', ]
[ Signature => $base64, ]
[ Method => 'relaxed', ]
[ Domain => 'example.org', ]
[ Identity => 'user@example.org', ]
[ Headers => 'from:subject:date:message-id', ]
[ Query => 'dns', ]
[ Selector => 'alpha', ]
[ Timestamp => time(), ]
[ Expiration => time() + 86400, ]
);
parse() - create a new signature from a DKIM-Signature header
my $sig = Mail::DKIM::Signature->parse(
'DKIM-Signature: a=rsa-sha1; b=yluiJ7+0=; c=relaxed'
);
Constructs a signature by parsing the provided DKIM-Signature header content. You do not have to include
the header name (i.e. "DKIM-Signature:") but it is recommended, so the header name can be preserved and
returned the same way in as_string().
Note: The input to this constructor is in the same format as the output of the as_string method.
METHODS
algorithm() - get or set the algorithm (a=) field
The algorithm used to generate the signature. Should be either "rsa-sha1", an RSA-signed SHA-1 digest, or
"rsa-sha256", an RSA-signed SHA-256 digest.
See also hash_algorithm().
as_string() - the signature header as a string
print $signature->as_string . "\n";
outputs
DKIM-Signature: a=rsa-sha1; b=yluiJ7+0=; c=relaxed
As shown in the example, the as_string method can be used to generate the DKIM-Signature that gets
prepended to a signed message.
as_string_without_data() - signature without the signature data
print $signature->as_string_without_data . "\n";
outputs
DKIM-Signature: a=rsa-sha1; b=; c=relaxed
This is similar to the as_string() method, but it always excludes the "data" part. This is used by the
DKIM canonicalization methods, which require incorporating this part of the signature into the signed
message.
body_count() - get or set the body count (l=) field
my $i = $signature->body_count;
Informs the verifier of the number of bytes in the body of the email included in the cryptographic hash,
starting from 0 immediately following the CRLF preceding the body. Also known as the l= tag.
When creating a signature, this tag may be either omitted, or set after the selected canonicalization
system has received the entire message body (but before it canonicalizes the DKIM-Signature).
body_hash() - get or set the body hash (bh=) field
my $bh = $signature->body_hash;
The hash of the body part of the message. Whitespace is ignored in this value. This tag is required.
When accessing this value, whitespace is stripped from the tag for you.
canonicalization() - get or set the canonicalization (c=) field
$signature->canonicalization('relaxed', 'simple');
($header, $body) = $signature->canonicalization;
Message canonicalization (default is "simple/simple"). This informs the verifier of the type of
canonicalization used to prepare the message for signing.
In scalar context, this returns header/body canonicalization as a single string separated by /. In list
context, it returns a two element array, containing first the header canonicalization, then the body.
data() - get or set the signature data (b=) field
my $base64 = $signature->data;
$signature->data($base64);
The signature data. Whitespace is automatically stripped from the returned value. The data is
Base64-encoded.
domain() - get or set the domain (d=) field
my $d = $signature->domain; # gets the domain value
$signature->domain('example.org'); # sets the domain value
The domain of the signing entity, as specified in the signature. This is the domain that will be queried
for the public key.
If using an "internationalized domain name", the domain name must be converted to ASCII (following
section 4.1 of RFC 3490) before passing it to this method.
expiration() - get or set the signature expiration (x=) field
Signature expiration (default is undef, meaning no expiration). The signature expiration, if defined, is
an unsigned integer identifying the standard Unix seconds-since-1970 time when the signature will expire.
get_public_key() - fetches the public key referenced by this signature
my $pubkey = $signature->get_public_key;
Public key to fetch is determined by the protocol, selector, and domain fields.
This method caches the result of the fetch, so subsequent calls will not require additional DNS queries.
This method will "die" if an error occurs.
get_tag() - access the raw value of a tag in this signature
my $raw_identity = $signature->get_tag('i');
Use this method to access a tag not already supported by Mail::DKIM, or if you want to bypass decoding of
the value by Mail::DKIM.
For example, the raw i= (identity) tag is encoded in quoted-printable form. If you use the identity()
method, Mail::DKIM will decode from quoted-printable before returning the value. But if you use
get_tag('i'), you can access the encoded quoted-printable form of the value.
hash_algorithm() - access the hash algorithm specified in this signature
my $hash = $signature->hash_algorithm;
Determines what hashing algorithm is used as part of the signature's specified algorithm.
For algorithm "rsa-sha1", the hash algorithm is "sha1". Likewise, for algorithm "rsa-sha256", the hash
algorithm is "sha256". If the algorithm is not recognized, undef is returned.
headerlist() - get or set the signed header fields (h=) field
$signature->headerlist('a:b:c');
my $headerlist = $signature->headerlist;
my @headers = $signature->headerlist;
Signed header fields. A colon-separated list of header field names that identify the header fields
presented to the signing algorithm.
In scalar context, the list of header field names will be returned as a single string, with the names
joined together with colons. In list context, the header field names will be returned as a list.
identity() - get or set the signing identity (i=) field
my $i = $signature->identity;
Identity of the user or agent on behalf of which this message is signed. The identity has an optional
local part, followed by "@", then a domain name. The domain name should be the same as or a subdomain of
the domain returned by the "domain" method.
Ideally, the identity should match the identity listed in the From: header, or the Sender: header, but
this is not required to have a valid signature. Whether the identity used is "authorized" to sign for the
given message is not determined here.
If using an "internationalized domain name", the domain name must be converted to ASCII (following
section 4.1 of RFC 3490) before passing it to this method.
Identity values are encoded in the signature in quoted-printable format. Using this method will
translate to/from quoted-printable as necessary. If you want the raw quoted-printable version of the
identity, use $signature->get_tag('i').
key() - get or set the private key object
my $key = $signature->key;
$signature->key(Mail::DKIM::PrivateKey->load(File => 'private.key'));
The private key is used for signing messages. It is not used for verifying messages.
The key object can be any object that implements the sign_digest() method. (Providing your own object
can be useful if your actual keys are stored out-of-process.)
method() - get or set the canonicalization (c=) field
Message canonicalization (default is "simple"). This informs the verifier of the type of canonicalization
used to prepare the message for signing.
protocol() - get or set the query methods (q=) field
A colon-separated list of query methods used to retrieve the public key (default is "dns"). Each query
method is of the form "type[/options]", where the syntax and semantics of the options depends on the
type.
result() - get or set the verification result
my $result = $signature->result;
$signature->result('pass');
# to set the result with details
$signature->result('invalid', 'no public key');
result_detail() - access the result, plus details if available
my $detail = $signature->result_detail;
An explanation of possible detail messages can be found in the documentation for "result_detail()" in
Mail::DKIM::Verifier.
selector() - get or set the selector (s=) field
The selector subdivides the namespace for the "d=" (domain) tag.
prettify() - alters the signature to look "nicer" as an email header
$signature->prettify;
This method may alter the signature in a way that breaks signatures, so it should be done ONLY when the
signature is being generated, BEFORE being fed to the canonicalization algorithm.
See also prettify_safe(), which will not break signatures.
prettify_safe() - same as prettify() but only touches the b= part
$signature->prettify_safe;
This method will not break the signature, but it only affects the b= part of the signature.
timestamp() - get or set the signature timestamp (t=) field
Signature timestamp (default is undef, meaning unknown creation time). This is the time that the
signature was created. The value is an unsigned integer identifying the number of standard Unix
seconds-since-1970.
version() - get or set the DKIM specification version (v=) field
This is the version of the DKIM specification that applies to this signature record.
SEE ALSO
Mail::DKIM::DkSignature for DomainKey-Signature headers
AUTHORS
• Jason Long <jason@long.name>
• Marc Bradshaw <marc@marcbradshaw.net>
• Bron Gondwana <brong@fastmailteam.com> (ARC)
THANKS
Work on ensuring that this module passes the ARC test suite was generously sponsored by Valimail
(https://www.valimail.com/)
COPYRIGHT AND LICENSE
• Copyright (C) 2013 by Messiah College
• Copyright (C) 2010 by Jason Long
• Copyright (C) 2017 by Standcore LLC
• Copyright (C) 2020 by FastMail Pty Ltd
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.
perl v5.38.2 2024-02-27 Mail::DKIM::Signature(3pm)