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Mail-DKIM2-0.18

Changes for version 0.18 - 2026-10-09

  • Fixes from an external review against spec-06. Several are behaviour changes for messages that are malformed or adversarial; well-formed mail verifies as before.
  • Behaviour change: only the signature algorithms rsa-sha256 and ed25519-sha256, matched exactly, are verified. An s= item naming anything else is ignored before its key is fetched (spec-06 §3.4); it used to be fetched and verified as RSA, so a correctly RSA-signed item declaring an unknown algorithm passed, and many distinct unknown names meant as many sequential DNS lookups. s= is parsed once, not once per item accessed. A signature whose items all name unknown algorithms is FAIL "has no signature with a supported algorithm"; a known item whose value is not a padded base64string is PERMERROR "syntax error"; a key of the wrong type for the algorithm is PERMERROR "algorithm mismatch".
  • Behaviour change: key records are validated whole (Mail::DKIM2::Common::parse_dkim_key_record, new): a repeated tag, v= not first or not exactly DKIM1, a missing, unpadded or non-base64 p=, or a p= that is not a key make the record a syntax error; an empty p= is revoked; k= other than rsa or ed25519 is no longer read as RSA. More than one TXT record for a selector is an error (one record in several strings is joined). The verifier reports these as spec-06 §11.5's PERMERRORs naming the selector, and a key absent for every item as PERMERROR "public key <sel> does not exist". parse_dkim_pubkey keeps its key-or-undef contract.
  • Behaviour change: Message-Instance tag names are case insignificant (spec-06 §7): M= and H= are read as m= and h= everywhere, and a tag repeated in any case is PERMERROR "syntax error" -- a wrong h= ahead of the right one used to be overwritten and pass.
  • Behaviour change: t= must be 1*DIGIT; anything else is PERMERROR "syntax error", even with SkipTimestampCheck, and t=0 is subject to the age check.
  • Behaviour change: a failed signature item reads "DKIM2-Signature i=N <selector> incorrect signature" (spec-06 §11.6).
  • Body Recipes come from a built-in capped Myers diff, the same algorithm as this repository's C, Python, Go and Mailman generators (vectors/body-diff.json); Algorithm::Diff is no longer a prerequisite. Repeated-line bodies no longer take quadratic time. A Recipe carries at most MaxRecipeLiterals literal lines (new calculate option, default 1000); over that the default path gives the null body Recipe, and EpilogueThreshold (no longer capped) the epilogue. dkim2-milter --max-recipe-literals and the DKIM2Sign handler's max_recipe_literals set it. An unchanged body under EpilogueThreshold gets no Recipe instead of an epilogue copy.
  • Behaviour change: every public constructor and class method that takes named options croaks on one it does not know, as the CONVENTIONS always said (Signature->new, MessageInstance calculate/verify/undo/chain_verifies, Gate->check, DSN generate/authenticate/propagate, MessageStore->new, Validate::report, fold_header).
  • Mail::DKIM2::DSN: authenticate and propagate take keys from DNS through Resolver when no PubkeyCallback is given, as documented; propagate croaks unless ForwarderDomain is the d= of the hop it strips; the POD says what ok means for an unsigned DSN.
  • Every eval in the library, Validate, Reflector and Split included, rethrows a host's exception object.
  • TagValueList/Signature parse() always returns a new object.
  • The README and Mail::DKIM2 SYNOPSIS sign and verify correctly, and t/synopsis.t runs them.

Documentation

dkim2-milter
Standalone DKIM2 milter for Postfix

Modules

Mail::DKIM2
DKIM2 signing and verification for email
Mail::DKIM2::Common
Canonicalization, hashing, folding and key handling for DKIM2
Mail::DKIM2::DSN
DKIM2-signed Delivery Status Notifications
Mail::DKIM2::Gate
decide whether a front end may sign a message
Mail::DKIM2::HeaderParser
Streaming message parser base for Signer and Verifier
Mail::DKIM2::MessageInstance
Compute, verify and undo Message-Instance headers
Mail::DKIM2::MessageStore
Keep message snapshots keyed by Message-Instance
Mail::DKIM2::Reflector
verify-and-reflect DKIM2 demonstration logic for dkim2.com
Mail::DKIM2::Signature
One DKIM2-Signature header, parsed or under construction
Mail::DKIM2::Signer
Sign a message with a DKIM2-Signature header
Mail::DKIM2::Split
Bcc-safe recipient grouping before DKIM2 signing
Mail::DKIM2::TagValueList
The tag=value list a DKIM2 header is made of
Mail::DKIM2::Validate
structured per-level DKIM2 and Message-Instance report
Mail::DKIM2::Verifier
Verify the DKIM2-Signature chain on a message
Mail::Milter::Authentication::Handler::DKIM2Sign
Handler class for DKIM2 signing
Mail::Milter::Authentication::Handler::DKIM2Verify
Handler class for DKIM2 signature verification

Examples

Other files