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RFC · CryptographyStandard explained

RFC 9420: Messaging Layer Security

Summary

RFC 9420 defines MLS for efficient end-to-end encryption in dynamic groups. Group encryption is more than pairwise encryption between many participants. Removed members must lose future access cryptographically.

Ideas

  • A ratchet tree distributes key changes in a scalable way.
  • Membership changes create new epochs.
  • Authentication and confidentiality are modelled separately.

Remarks

  • RFC 9420 has the status “Proposed Standard”; current errata and successor documents should also be checked.

Recommendations

  • Use reviewed MLS libraries instead of your own group ratchets.
  • Protect identity binding and device synchronisation as well as message keys.

References

Read the RFC at the RFC Editor

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