Mail::DKIM::Signature(3)

NAME
Mail::DKIM::Signature - represents a DKIM-Signature header

VERSION
version 1.20240923

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 one of the following: - "rsa-sha1",an RSA-signed SHA-1 digest - "rsa-sha256", an RSA-signed SHA-256 digest - "ed25519-sha256", an Ed25519-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.