It appears that Wei Chuang <[email protected]> said: >We've written the following DKIM threat model as a starting point: > >The DKIM Working Group requests guidance from the CFRG in identifying the >most appropriate Post-Quantum Cryptography (PQC) digital signature >algorithm for DomainKeys Identified Mail. Our primary threat model focuses >on an adversary utilizing quantum analytic key compromise to forge >signatures, thereby enabling widespread domain spoofing. To maintain the >reliability of global email delivery, any proposed algorithm must navigate >DKIM's strict operational constraints: public keys are distributed via DNS >TXT records (imposing severe sensitivity to UDP payload limits and TCP >fallback latency), and signatures are transmitted within standard email >headers. Furthermore, DKIM’s existing architecture evaluates the message >hash independently of the signature generation to facilitate the processing >of streamed email bodies. We seek CFRG’s expertise in selecting an >algorithm that optimizes for these stringent size constraints while >providing secure, practical recommendations for accommodating our >pre-hashed input model.
DKIM is intended for protection of messages in transit, which typically takes under a minute and rarely more than a few days. Hence "harvest now decrypt later" is unlikely to be a threat. DKIM keys should be short in order to fit in UDP DNS packets, which means ideally they are only a few hundred octets. If they are larger, that means requests will fall back to TCP which is not ideal but not terrible. DNS has a 64K limit for the combined size of everything in a DNS message which puts a pratical limit of about 20K on the size of a key record. DKIM signatures are stored in e-mail message header fields which have no formal length limit, and in practice are often several thousand octets. Both the keys and the signatures are ASCII, with binary values represented in base64 which is 4/3 the size of the binary. R's, John _______________________________________________ Ietf-dkim mailing list -- [email protected] To unsubscribe send an email to [email protected]
