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CFRG discussion on ChaCha20

CFRG discussion on ChaCha20 . mcgrew@cisco.com TLS Working Group @ IETF 89. Background. TLS chairs asked CFRG chairs to provide an update on ChaCha and Poly1305 (2/23) CFRG chairs offered input on new ECC CFRG agenda included questions

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CFRG discussion on ChaCha20

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  1. CFRG discussion on ChaCha20 mcgrew@cisco.com TLS Working Group @ IETF 89

  2. Background • TLS chairs asked CFRG chairs to provide an update on ChaCha and Poly1305 (2/23) • CFRG chairs offered input on new ECC • CFRG agenda included questions http://www.ietf.org/proceedings/89/slides/slides-89-cfrg-0.pptx • We suggest that the request from TLS to CFRG be formalized • To what questions should we seek answers?

  3. ChaCha20 and Poly1305 • Points made in CFRG • ChaCha20 should not be used as a stream cipher • AEAD construction is preferable • draft-nir-cfrg-chacha20-poly1305-00 should be advanced and reviewed more • The composition of ChaCha and Poly1305 is novel and needs review • Let’s seek input from Dan Bernstein • Hum on “do you think this function is adequately secure to be used in TLS ciphersuites?” • Few agreed, 1 or 2 disagreed, many felt unsuited to respond • Note that the room has a lower proportion of cryptanalysts than list • Suggestion: • Proceed with draft-nir-cfrg-chacha20-poly1305-00, expecting tweaks, with a one month period to review draft-nir-cfrg-chacha20-poly1305-00 in CFRG

  4. New ECC • Curve25519 • draft-josefsson-tls-curve25519-01 • Montgomery form • Not suitable for signatures • draft-ladd-safecurves-01 • Montgomery and Edwards form • DJB: safecurves not all equally well performing

  5. CFRG Conclusion on New ECC • Focus on doing one new curve family • Aim for reusability beyond TLS (SSH, IKE, …) • CFRG should have an interim meeting dedicated to the discussion of New ECC • Teleconference will be accessible to more CFRG members • 20+ interested in participating • Early April (one month to prepare) • Identify goals in advance • Solicit written input and presentations

  6. What questions should we ask CFRG? • Should be specific to drafts when possible • Should be written down • Email sent to CFRG and TLS list • Could be debated on list and finalized by chairs • Should have a cutoff date (~3 months) • Should consider general suitability, and not just security • Should provide goals, or accept input on goals

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