Glossary
Email authentication
Body hash (bh=)
A hash of the canonicalised message body carried in the signature. If the body changes in transit the body hash no longer matches and verification fails before the signature is even checked.
Defined in RFC 6376 §3.7.
Where this appears
The lessons that use this term, and what each is for.
Email Authentication FundamentalsWhat a DKIM signature provesState what a valid DKIM signature establishes, and what it deliberately leaves open.Email Authentication FundamentalsAnatomy of a DKIM-Signature headerRead a DKIM-Signature header and say which domain is making the claim and which headers it covers.DKIM PractitionerThe two hashesSay precisely which bytes of a message a signature commits to, and which it does not.DKIM PractitionerDKIM-Signature, tag by tagRead any DKIM-Signature header and state what each tag contributes to the verification.DKIM PractitionerRelaxed and simplePredict which whitespace and header changes each canonicalisation survives.DKIM PractitionerWhat breaks a signature in transitName the intermediary responsible when a signature that was valid at send fails at delivery.DKIM PractitionerRotations that lose mailName the four ways a rotation destroys signatures, and the check that catches each.DKIM Practitionerbody hash did not verifyIdentify what modified a message from the fact that only the body hash failed.DKIM PractitionerSignature replayExplain how a valid signature is abused after the fact, and what limits the damage.