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matrix-spec/proposals/xxxx-sas-v2.md
Hubert Chathi 86d0d04ed1 don't include unrelated changes
2020-05-11 11:54:50 -04:00

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SAS verification, v2

Proposal

A new key_agreement_protocol, curve25519-hkdf-sha256 is introduced. It is the same as curve25519 except that the info parameter for the HKDF is the concatenation of:

  • The string MATRIX_KEY_VERIFICATION_SAS|.
  • The Matrix ID of the user who sent the m.key.verification.start message, followed by |.
  • The Device ID of the device which sent the m.key.verification.start message, followed by |.
  • The public key from the m.key.verification.key message sent by the device which sent the m.key.verification.start message, followed by |.
  • The Matrix ID of the user who sent the m.key.verification.accept message, followed by |.
  • The Device ID of the device which sent the m.key.verification.accept message, followed by |.
  • The public key from the m.key.verification.key message sent by the device which sent the m.key.verification.accept message, followed by |.
  • The transaction_id being used.

The differences from curve25519 are the addition of the public keys, and the addition of | as delimiter between the fields.

The key_agreement_protocol curve25519 is deprecated and may be removed in the future.

Potential issues

Alternatives

Security considerations

Unstable prefix