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Ephemeral keys

Receiving key, outgoing viewing key
Ephemeral keys are used to encrypt transaction data (accounts and notes). The symmetric cipher algorithm (ChaCha20Poly1305) which applies to the memo block is required to use different keys for security reasons.
There are two cases where ephemeral keys are generated: notes encryption and shared secrets encryption. In both cases ephemeral keys are derived from the random secret keys generated before the each encryption operation. The account's intermediate key is used for the derivation process.
  • The receiving key is a set of the intermediate key
    η\eta
    and ephemeral public key
    AiAi
    . These are used to derive the note encryption key. Successfully decrypted notes with the
    η\eta
    key are considered received keys by a client.
  • The outgoing viewing key is used to decrypt shared secrets in the memo block. Shared secrets contain symmetric keys which are used to decrypt the output account and notes for the current transaction.
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