697 lines
25 KiB
Rust
697 lines
25 KiB
Rust
//! Note encryption for Zcash transactions.
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//!
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//! This crate implements the [in-band secret distribution scheme] for the Sapling and
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//! Orchard protocols. It provides reusable methods that implement common note encryption
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//! and trial decryption logic, and enforce protocol-agnostic verification requirements.
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//!
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//! Protocol-specific logic is handled via the [`Domain`] trait. Implementations of this
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//! trait are provided in the [`zcash_primitives`] (for Sapling) and [`orchard`] crates;
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//! users with their own existing types can similarly implement the trait themselves.
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//!
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//! [in-band secret distribution scheme]: https://zips.z.cash/protocol/protocol.pdf#saplingandorchardinband
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//! [`zcash_primitives`]: https://crates.io/crates/zcash_primitives
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//! [`orchard`]: https://crates.io/crates/orchard
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#![no_std]
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#![cfg_attr(docsrs, feature(doc_cfg))]
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// Catch documentation errors caused by code changes.
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#![deny(rustdoc::broken_intra_doc_links)]
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#![deny(unsafe_code)]
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// TODO: #![deny(missing_docs)]
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use core::fmt::{self, Write};
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#[cfg(feature = "alloc")]
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extern crate alloc;
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#[cfg(feature = "alloc")]
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use alloc::vec::Vec;
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use chacha20::{
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cipher::{StreamCipher, StreamCipherSeek},
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ChaCha20,
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};
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use chacha20poly1305::{aead::AeadInPlace, ChaCha20Poly1305, KeyInit};
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use cipher::KeyIvInit;
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use rand_core::RngCore;
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use subtle::{Choice, ConstantTimeEq};
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#[cfg(feature = "alloc")]
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#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
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pub mod batch;
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/// The size of a compact note.
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pub const COMPACT_NOTE_SIZE: usize = 1 + // version
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11 + // diversifier
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8 + // value
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32; // rseed (or rcm prior to ZIP 212)
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/// The size of [`NotePlaintextBytes`].
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pub const NOTE_PLAINTEXT_SIZE: usize = COMPACT_NOTE_SIZE + 512;
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/// The size of [`OutPlaintextBytes`].
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pub const OUT_PLAINTEXT_SIZE: usize = 32 + // pk_d
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32; // esk
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const AEAD_TAG_SIZE: usize = 16;
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/// The size of an encrypted note plaintext.
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pub const ENC_CIPHERTEXT_SIZE: usize = NOTE_PLAINTEXT_SIZE + AEAD_TAG_SIZE;
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/// The size of an encrypted outgoing plaintext.
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pub const OUT_CIPHERTEXT_SIZE: usize = OUT_PLAINTEXT_SIZE + AEAD_TAG_SIZE;
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/// A symmetric key that can be used to recover a single Sapling or Orchard output.
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pub struct OutgoingCipherKey(pub [u8; 32]);
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impl From<[u8; 32]> for OutgoingCipherKey {
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fn from(ock: [u8; 32]) -> Self {
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OutgoingCipherKey(ock)
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}
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}
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impl AsRef<[u8]> for OutgoingCipherKey {
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fn as_ref(&self) -> &[u8] {
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&self.0
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}
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}
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/// Newtype representing the byte encoding of an [`EphemeralPublicKey`].
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///
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/// [`EphemeralPublicKey`]: Domain::EphemeralPublicKey
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#[derive(Clone)]
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pub struct EphemeralKeyBytes(pub [u8; 32]);
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impl fmt::Debug for EphemeralKeyBytes {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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struct HexFmt<'b>(&'b [u8]);
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impl<'b> fmt::Debug for HexFmt<'b> {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.write_char('"')?;
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for b in self.0 {
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f.write_fmt(format_args!("{:02x}", b))?;
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}
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f.write_char('"')
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}
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}
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f.debug_tuple("EphemeralKeyBytes")
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.field(&HexFmt(&self.0))
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.finish()
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}
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}
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impl AsRef<[u8]> for EphemeralKeyBytes {
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fn as_ref(&self) -> &[u8] {
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&self.0
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}
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}
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impl From<[u8; 32]> for EphemeralKeyBytes {
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fn from(value: [u8; 32]) -> EphemeralKeyBytes {
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EphemeralKeyBytes(value)
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}
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}
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impl ConstantTimeEq for EphemeralKeyBytes {
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fn ct_eq(&self, other: &Self) -> Choice {
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self.0.ct_eq(&other.0)
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}
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}
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/// Newtype representing the byte encoding of a note plaintext.
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pub struct NotePlaintextBytes(pub [u8; NOTE_PLAINTEXT_SIZE]);
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/// Newtype representing the byte encoding of a outgoing plaintext.
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pub struct OutPlaintextBytes(pub [u8; OUT_PLAINTEXT_SIZE]);
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#[derive(Copy, Clone, PartialEq, Eq)]
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enum NoteValidity {
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Valid,
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Invalid,
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}
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/// Trait that encapsulates protocol-specific note encryption types and logic.
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///
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/// This trait enables most of the note encryption logic to be shared between Sapling and
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/// Orchard, as well as between different implementations of those protocols.
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pub trait Domain {
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type EphemeralSecretKey: ConstantTimeEq;
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type EphemeralPublicKey;
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type PreparedEphemeralPublicKey;
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type SharedSecret;
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type SymmetricKey: AsRef<[u8]>;
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type Note;
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type Recipient;
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type DiversifiedTransmissionKey;
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type IncomingViewingKey;
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type OutgoingViewingKey;
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type ValueCommitment;
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type ExtractedCommitment;
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type ExtractedCommitmentBytes: Eq + for<'a> From<&'a Self::ExtractedCommitment>;
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type Memo;
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/// Derives the `EphemeralSecretKey` corresponding to this note.
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///
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/// Returns `None` if the note was created prior to [ZIP 212], and doesn't have a
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/// deterministic `EphemeralSecretKey`.
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///
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/// [ZIP 212]: https://zips.z.cash/zip-0212
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fn derive_esk(note: &Self::Note) -> Option<Self::EphemeralSecretKey>;
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/// Extracts the `DiversifiedTransmissionKey` from the note.
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fn get_pk_d(note: &Self::Note) -> Self::DiversifiedTransmissionKey;
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/// Prepare an ephemeral public key for more efficient scalar multiplication.
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fn prepare_epk(epk: Self::EphemeralPublicKey) -> Self::PreparedEphemeralPublicKey;
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/// Derives `EphemeralPublicKey` from `esk` and the note's diversifier.
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fn ka_derive_public(
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note: &Self::Note,
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esk: &Self::EphemeralSecretKey,
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) -> Self::EphemeralPublicKey;
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/// Derives the `SharedSecret` from the sender's information during note encryption.
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fn ka_agree_enc(
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esk: &Self::EphemeralSecretKey,
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pk_d: &Self::DiversifiedTransmissionKey,
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) -> Self::SharedSecret;
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/// Derives the `SharedSecret` from the recipient's information during note trial
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/// decryption.
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fn ka_agree_dec(
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ivk: &Self::IncomingViewingKey,
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epk: &Self::PreparedEphemeralPublicKey,
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) -> Self::SharedSecret;
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/// Derives the `SymmetricKey` used to encrypt the note plaintext.
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///
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/// `secret` is the `SharedSecret` obtained from [`Self::ka_agree_enc`] or
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/// [`Self::ka_agree_dec`].
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///
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/// `ephemeral_key` is the byte encoding of the [`EphemeralPublicKey`] used to derive
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/// `secret`. During encryption it is derived via [`Self::epk_bytes`]; during trial
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/// decryption it is obtained from [`ShieldedOutput::ephemeral_key`].
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///
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/// [`EphemeralPublicKey`]: Self::EphemeralPublicKey
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/// [`EphemeralSecretKey`]: Self::EphemeralSecretKey
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fn kdf(secret: Self::SharedSecret, ephemeral_key: &EphemeralKeyBytes) -> Self::SymmetricKey;
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/// Encodes the given `Note` and `Memo` as a note plaintext.
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fn note_plaintext_bytes(note: &Self::Note, memo: &Self::Memo) -> NotePlaintextBytes;
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/// Derives the [`OutgoingCipherKey`] for an encrypted note, given the note-specific
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/// public data and an `OutgoingViewingKey`.
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fn derive_ock(
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ovk: &Self::OutgoingViewingKey,
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cv: &Self::ValueCommitment,
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cmstar_bytes: &Self::ExtractedCommitmentBytes,
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ephemeral_key: &EphemeralKeyBytes,
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) -> OutgoingCipherKey;
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/// Encodes the outgoing plaintext for the given note.
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fn outgoing_plaintext_bytes(
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note: &Self::Note,
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esk: &Self::EphemeralSecretKey,
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) -> OutPlaintextBytes;
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/// Returns the byte encoding of the given `EphemeralPublicKey`.
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fn epk_bytes(epk: &Self::EphemeralPublicKey) -> EphemeralKeyBytes;
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/// Attempts to parse `ephemeral_key` as an `EphemeralPublicKey`.
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///
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/// Returns `None` if `ephemeral_key` is not a valid byte encoding of an
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/// `EphemeralPublicKey`.
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fn epk(ephemeral_key: &EphemeralKeyBytes) -> Option<Self::EphemeralPublicKey>;
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/// Derives the `ExtractedCommitment` for this note.
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fn cmstar(note: &Self::Note) -> Self::ExtractedCommitment;
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/// Parses the given note plaintext from the recipient's perspective.
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///
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/// The implementation of this method must check that:
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/// - The note plaintext version is valid (for the given decryption domain's context,
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/// which may be passed via `self`).
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/// - The note plaintext contains valid encodings of its various fields.
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/// - Any domain-specific requirements are satisfied.
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///
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/// `&self` is passed here to enable the implementation to enforce contextual checks,
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/// such as rules like [ZIP 212] that become active at a specific block height.
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///
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/// [ZIP 212]: https://zips.z.cash/zip-0212
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///
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/// # Panics
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///
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/// Panics if `plaintext` is shorter than [`COMPACT_NOTE_SIZE`].
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fn parse_note_plaintext_without_memo_ivk(
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&self,
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ivk: &Self::IncomingViewingKey,
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plaintext: &[u8],
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) -> Option<(Self::Note, Self::Recipient)>;
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/// Parses the given note plaintext from the sender's perspective.
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///
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/// The implementation of this method must check that:
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/// - The note plaintext version is valid (for the given decryption domain's context,
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/// which may be passed via `self`).
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/// - The note plaintext contains valid encodings of its various fields.
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/// - Any domain-specific requirements are satisfied.
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///
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/// `&self` is passed here to enable the implementation to enforce contextual checks,
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/// such as rules like [ZIP 212] that become active at a specific block height.
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///
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/// [ZIP 212]: https://zips.z.cash/zip-0212
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fn parse_note_plaintext_without_memo_ovk(
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&self,
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pk_d: &Self::DiversifiedTransmissionKey,
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plaintext: &NotePlaintextBytes,
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) -> Option<(Self::Note, Self::Recipient)>;
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/// Extracts the memo field from the given note plaintext.
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///
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/// # Compatibility
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///
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/// `&self` is passed here in anticipation of future changes to memo handling, where
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/// the memos may no longer be part of the note plaintext.
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fn extract_memo(&self, plaintext: &NotePlaintextBytes) -> Self::Memo;
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/// Parses the `DiversifiedTransmissionKey` field of the outgoing plaintext.
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///
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/// Returns `None` if `out_plaintext` does not contain a valid byte encoding of a
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/// `DiversifiedTransmissionKey`.
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fn extract_pk_d(out_plaintext: &OutPlaintextBytes) -> Option<Self::DiversifiedTransmissionKey>;
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/// Parses the `EphemeralSecretKey` field of the outgoing plaintext.
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///
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/// Returns `None` if `out_plaintext` does not contain a valid byte encoding of an
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/// `EphemeralSecretKey`.
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fn extract_esk(out_plaintext: &OutPlaintextBytes) -> Option<Self::EphemeralSecretKey>;
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}
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/// Trait that encapsulates protocol-specific batch trial decryption logic.
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///
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/// Each batchable operation has a default implementation that calls through to the
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/// non-batched implementation. Domains can override whichever operations benefit from
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/// batched logic.
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#[cfg(feature = "alloc")]
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#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
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pub trait BatchDomain: Domain {
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/// Computes `Self::kdf` on a batch of items.
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///
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/// For each item in the batch, if the shared secret is `None`, this returns `None` at
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/// that position.
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fn batch_kdf<'a>(
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items: impl Iterator<Item = (Option<Self::SharedSecret>, &'a EphemeralKeyBytes)>,
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) -> Vec<Option<Self::SymmetricKey>> {
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// Default implementation: do the non-batched thing.
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items
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.map(|(secret, ephemeral_key)| secret.map(|secret| Self::kdf(secret, ephemeral_key)))
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.collect()
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}
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/// Computes `Self::epk` on a batch of ephemeral keys.
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///
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/// This is useful for protocols where the underlying curve requires an inversion to
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/// parse an encoded point.
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///
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/// For usability, this returns tuples of the ephemeral keys and the result of parsing
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/// them.
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fn batch_epk(
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ephemeral_keys: impl Iterator<Item = EphemeralKeyBytes>,
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) -> Vec<(Option<Self::PreparedEphemeralPublicKey>, EphemeralKeyBytes)> {
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// Default implementation: do the non-batched thing.
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ephemeral_keys
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.map(|ephemeral_key| {
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(
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Self::epk(&ephemeral_key).map(Self::prepare_epk),
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ephemeral_key,
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)
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})
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.collect()
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}
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}
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/// Trait that provides access to the components of an encrypted transaction output.
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///
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/// Implementations of this trait are required to define the length of their ciphertext
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/// field. In order to use the trial decryption APIs in this crate, the length must be
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/// either [`ENC_CIPHERTEXT_SIZE`] or [`COMPACT_NOTE_SIZE`].
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pub trait ShieldedOutput<D: Domain, const CIPHERTEXT_SIZE: usize> {
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/// Exposes the `ephemeral_key` field of the output.
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fn ephemeral_key(&self) -> EphemeralKeyBytes;
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/// Exposes the `cmu_bytes` or `cmx_bytes` field of the output.
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fn cmstar_bytes(&self) -> D::ExtractedCommitmentBytes;
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/// Exposes the note ciphertext of the output.
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fn enc_ciphertext(&self) -> &[u8; CIPHERTEXT_SIZE];
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}
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/// A struct containing context required for encrypting Sapling and Orchard notes.
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///
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/// This struct provides a safe API for encrypting Sapling and Orchard notes. In particular, it
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/// enforces that fresh ephemeral keys are used for every note, and that the ciphertexts are
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/// consistent with each other.
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///
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/// Implements section 4.19 of the
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/// [Zcash Protocol Specification](https://zips.z.cash/protocol/nu5.pdf#saplingandorchardinband)
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pub struct NoteEncryption<D: Domain> {
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epk: D::EphemeralPublicKey,
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esk: D::EphemeralSecretKey,
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note: D::Note,
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memo: D::Memo,
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/// `None` represents the `ovk = ⊥` case.
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ovk: Option<D::OutgoingViewingKey>,
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}
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impl<D: Domain> NoteEncryption<D> {
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/// Construct a new note encryption context for the specified note,
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/// recipient, and memo.
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pub fn new(ovk: Option<D::OutgoingViewingKey>, note: D::Note, memo: D::Memo) -> Self {
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let esk = D::derive_esk(¬e).expect("ZIP 212 is active.");
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NoteEncryption {
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epk: D::ka_derive_public(¬e, &esk),
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esk,
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note,
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memo,
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ovk,
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}
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}
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/// For use only with Sapling. This method is preserved in order that test code
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/// be able to generate pre-ZIP-212 ciphertexts so that tests can continue to
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/// cover pre-ZIP-212 transaction decryption.
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#[cfg(feature = "pre-zip-212")]
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#[cfg_attr(docsrs, doc(cfg(feature = "pre-zip-212")))]
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pub fn new_with_esk(
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esk: D::EphemeralSecretKey,
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ovk: Option<D::OutgoingViewingKey>,
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note: D::Note,
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memo: D::Memo,
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) -> Self {
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NoteEncryption {
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epk: D::ka_derive_public(¬e, &esk),
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esk,
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note,
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memo,
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ovk,
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}
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}
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/// Exposes the ephemeral secret key being used to encrypt this note.
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pub fn esk(&self) -> &D::EphemeralSecretKey {
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&self.esk
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}
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/// Exposes the encoding of the ephemeral public key being used to encrypt this note.
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pub fn epk(&self) -> &D::EphemeralPublicKey {
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&self.epk
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}
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/// Generates `encCiphertext` for this note.
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pub fn encrypt_note_plaintext(&self) -> [u8; ENC_CIPHERTEXT_SIZE] {
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let pk_d = D::get_pk_d(&self.note);
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let shared_secret = D::ka_agree_enc(&self.esk, &pk_d);
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let key = D::kdf(shared_secret, &D::epk_bytes(&self.epk));
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let input = D::note_plaintext_bytes(&self.note, &self.memo);
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let mut output = [0u8; ENC_CIPHERTEXT_SIZE];
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output[..NOTE_PLAINTEXT_SIZE].copy_from_slice(&input.0);
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let tag = ChaCha20Poly1305::new(key.as_ref().into())
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.encrypt_in_place_detached(
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[0u8; 12][..].into(),
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&[],
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&mut output[..NOTE_PLAINTEXT_SIZE],
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)
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.unwrap();
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output[NOTE_PLAINTEXT_SIZE..].copy_from_slice(&tag);
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output
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}
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/// Generates `outCiphertext` for this note.
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pub fn encrypt_outgoing_plaintext<R: RngCore>(
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&self,
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cv: &D::ValueCommitment,
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cmstar: &D::ExtractedCommitment,
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rng: &mut R,
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) -> [u8; OUT_CIPHERTEXT_SIZE] {
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let (ock, input) = if let Some(ovk) = &self.ovk {
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let ock = D::derive_ock(ovk, cv, &cmstar.into(), &D::epk_bytes(&self.epk));
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let input = D::outgoing_plaintext_bytes(&self.note, &self.esk);
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(ock, input)
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} else {
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// ovk = ⊥
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let mut ock = OutgoingCipherKey([0; 32]);
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let mut input = [0u8; OUT_PLAINTEXT_SIZE];
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rng.fill_bytes(&mut ock.0);
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rng.fill_bytes(&mut input);
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(ock, OutPlaintextBytes(input))
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};
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let mut output = [0u8; OUT_CIPHERTEXT_SIZE];
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output[..OUT_PLAINTEXT_SIZE].copy_from_slice(&input.0);
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let tag = ChaCha20Poly1305::new(ock.as_ref().into())
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.encrypt_in_place_detached([0u8; 12][..].into(), &[], &mut output[..OUT_PLAINTEXT_SIZE])
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.unwrap();
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output[OUT_PLAINTEXT_SIZE..].copy_from_slice(&tag);
|
||
|
||
output
|
||
}
|
||
}
|
||
|
||
/// Trial decryption of the full note plaintext by the recipient.
|
||
///
|
||
/// Attempts to decrypt and validate the given shielded output using the given `ivk`.
|
||
/// If successful, the corresponding note and memo are returned, along with the address to
|
||
/// which the note was sent.
|
||
///
|
||
/// Implements section 4.19.2 of the
|
||
/// [Zcash Protocol Specification](https://zips.z.cash/protocol/nu5.pdf#decryptivk).
|
||
pub fn try_note_decryption<D: Domain, Output: ShieldedOutput<D, ENC_CIPHERTEXT_SIZE>>(
|
||
domain: &D,
|
||
ivk: &D::IncomingViewingKey,
|
||
output: &Output,
|
||
) -> Option<(D::Note, D::Recipient, D::Memo)> {
|
||
let ephemeral_key = output.ephemeral_key();
|
||
|
||
let epk = D::prepare_epk(D::epk(&ephemeral_key)?);
|
||
let shared_secret = D::ka_agree_dec(ivk, &epk);
|
||
let key = D::kdf(shared_secret, &ephemeral_key);
|
||
|
||
try_note_decryption_inner(domain, ivk, &ephemeral_key, output, &key)
|
||
}
|
||
|
||
fn try_note_decryption_inner<D: Domain, Output: ShieldedOutput<D, ENC_CIPHERTEXT_SIZE>>(
|
||
domain: &D,
|
||
ivk: &D::IncomingViewingKey,
|
||
ephemeral_key: &EphemeralKeyBytes,
|
||
output: &Output,
|
||
key: &D::SymmetricKey,
|
||
) -> Option<(D::Note, D::Recipient, D::Memo)> {
|
||
let enc_ciphertext = output.enc_ciphertext();
|
||
|
||
let mut plaintext =
|
||
NotePlaintextBytes(enc_ciphertext[..NOTE_PLAINTEXT_SIZE].try_into().unwrap());
|
||
|
||
ChaCha20Poly1305::new(key.as_ref().into())
|
||
.decrypt_in_place_detached(
|
||
[0u8; 12][..].into(),
|
||
&[],
|
||
&mut plaintext.0,
|
||
enc_ciphertext[NOTE_PLAINTEXT_SIZE..].into(),
|
||
)
|
||
.ok()?;
|
||
|
||
let (note, to) = parse_note_plaintext_without_memo_ivk(
|
||
domain,
|
||
ivk,
|
||
ephemeral_key,
|
||
&output.cmstar_bytes(),
|
||
&plaintext.0,
|
||
)?;
|
||
let memo = domain.extract_memo(&plaintext);
|
||
|
||
Some((note, to, memo))
|
||
}
|
||
|
||
fn parse_note_plaintext_without_memo_ivk<D: Domain>(
|
||
domain: &D,
|
||
ivk: &D::IncomingViewingKey,
|
||
ephemeral_key: &EphemeralKeyBytes,
|
||
cmstar_bytes: &D::ExtractedCommitmentBytes,
|
||
plaintext: &[u8],
|
||
) -> Option<(D::Note, D::Recipient)> {
|
||
let (note, to) = domain.parse_note_plaintext_without_memo_ivk(ivk, plaintext)?;
|
||
|
||
if let NoteValidity::Valid = check_note_validity::<D>(¬e, ephemeral_key, cmstar_bytes) {
|
||
Some((note, to))
|
||
} else {
|
||
None
|
||
}
|
||
}
|
||
|
||
fn check_note_validity<D: Domain>(
|
||
note: &D::Note,
|
||
ephemeral_key: &EphemeralKeyBytes,
|
||
cmstar_bytes: &D::ExtractedCommitmentBytes,
|
||
) -> NoteValidity {
|
||
if &D::ExtractedCommitmentBytes::from(&D::cmstar(note)) == cmstar_bytes {
|
||
// In the case corresponding to specification section 4.19.3, we check that `esk` is equal
|
||
// to `D::derive_esk(note)` prior to calling this method.
|
||
if let Some(derived_esk) = D::derive_esk(note) {
|
||
if D::epk_bytes(&D::ka_derive_public(note, &derived_esk))
|
||
.ct_eq(ephemeral_key)
|
||
.into()
|
||
{
|
||
NoteValidity::Valid
|
||
} else {
|
||
NoteValidity::Invalid
|
||
}
|
||
} else {
|
||
// Before ZIP 212
|
||
NoteValidity::Valid
|
||
}
|
||
} else {
|
||
// Published commitment doesn't match calculated commitment
|
||
NoteValidity::Invalid
|
||
}
|
||
}
|
||
|
||
/// Trial decryption of the compact note plaintext by the recipient for light clients.
|
||
///
|
||
/// Attempts to decrypt and validate the given compact shielded output using the
|
||
/// given `ivk`. If successful, the corresponding note is returned, along with the address
|
||
/// to which the note was sent.
|
||
///
|
||
/// Implements the procedure specified in [`ZIP 307`].
|
||
///
|
||
/// [`ZIP 307`]: https://zips.z.cash/zip-0307
|
||
pub fn try_compact_note_decryption<D: Domain, Output: ShieldedOutput<D, COMPACT_NOTE_SIZE>>(
|
||
domain: &D,
|
||
ivk: &D::IncomingViewingKey,
|
||
output: &Output,
|
||
) -> Option<(D::Note, D::Recipient)> {
|
||
let ephemeral_key = output.ephemeral_key();
|
||
|
||
let epk = D::prepare_epk(D::epk(&ephemeral_key)?);
|
||
let shared_secret = D::ka_agree_dec(ivk, &epk);
|
||
let key = D::kdf(shared_secret, &ephemeral_key);
|
||
|
||
try_compact_note_decryption_inner(domain, ivk, &ephemeral_key, output, &key)
|
||
}
|
||
|
||
fn try_compact_note_decryption_inner<D: Domain, Output: ShieldedOutput<D, COMPACT_NOTE_SIZE>>(
|
||
domain: &D,
|
||
ivk: &D::IncomingViewingKey,
|
||
ephemeral_key: &EphemeralKeyBytes,
|
||
output: &Output,
|
||
key: &D::SymmetricKey,
|
||
) -> Option<(D::Note, D::Recipient)> {
|
||
// Start from block 1 to skip over Poly1305 keying output
|
||
let mut plaintext = [0; COMPACT_NOTE_SIZE];
|
||
plaintext.copy_from_slice(output.enc_ciphertext());
|
||
let mut keystream = ChaCha20::new(key.as_ref().into(), [0u8; 12][..].into());
|
||
keystream.seek(64);
|
||
keystream.apply_keystream(&mut plaintext);
|
||
|
||
parse_note_plaintext_without_memo_ivk(
|
||
domain,
|
||
ivk,
|
||
ephemeral_key,
|
||
&output.cmstar_bytes(),
|
||
&plaintext,
|
||
)
|
||
}
|
||
|
||
/// Recovery of the full note plaintext by the sender.
|
||
///
|
||
/// Attempts to decrypt and validate the given shielded output using the given `ovk`.
|
||
/// If successful, the corresponding note and memo are returned, along with the address to
|
||
/// which the note was sent.
|
||
///
|
||
/// Implements [Zcash Protocol Specification section 4.19.3][decryptovk].
|
||
///
|
||
/// [decryptovk]: https://zips.z.cash/protocol/nu5.pdf#decryptovk
|
||
pub fn try_output_recovery_with_ovk<D: Domain, Output: ShieldedOutput<D, ENC_CIPHERTEXT_SIZE>>(
|
||
domain: &D,
|
||
ovk: &D::OutgoingViewingKey,
|
||
output: &Output,
|
||
cv: &D::ValueCommitment,
|
||
out_ciphertext: &[u8; OUT_CIPHERTEXT_SIZE],
|
||
) -> Option<(D::Note, D::Recipient, D::Memo)> {
|
||
let ock = D::derive_ock(ovk, cv, &output.cmstar_bytes(), &output.ephemeral_key());
|
||
try_output_recovery_with_ock(domain, &ock, output, out_ciphertext)
|
||
}
|
||
|
||
/// Recovery of the full note plaintext by the sender.
|
||
///
|
||
/// Attempts to decrypt and validate the given shielded output using the given `ock`.
|
||
/// If successful, the corresponding note and memo are returned, along with the address to
|
||
/// which the note was sent.
|
||
///
|
||
/// Implements part of section 4.19.3 of the
|
||
/// [Zcash Protocol Specification](https://zips.z.cash/protocol/nu5.pdf#decryptovk).
|
||
/// For decryption using a Full Viewing Key see [`try_output_recovery_with_ovk`].
|
||
pub fn try_output_recovery_with_ock<D: Domain, Output: ShieldedOutput<D, ENC_CIPHERTEXT_SIZE>>(
|
||
domain: &D,
|
||
ock: &OutgoingCipherKey,
|
||
output: &Output,
|
||
out_ciphertext: &[u8; OUT_CIPHERTEXT_SIZE],
|
||
) -> Option<(D::Note, D::Recipient, D::Memo)> {
|
||
let enc_ciphertext = output.enc_ciphertext();
|
||
|
||
let mut op = OutPlaintextBytes([0; OUT_PLAINTEXT_SIZE]);
|
||
op.0.copy_from_slice(&out_ciphertext[..OUT_PLAINTEXT_SIZE]);
|
||
|
||
ChaCha20Poly1305::new(ock.as_ref().into())
|
||
.decrypt_in_place_detached(
|
||
[0u8; 12][..].into(),
|
||
&[],
|
||
&mut op.0,
|
||
out_ciphertext[OUT_PLAINTEXT_SIZE..].into(),
|
||
)
|
||
.ok()?;
|
||
|
||
let pk_d = D::extract_pk_d(&op)?;
|
||
let esk = D::extract_esk(&op)?;
|
||
|
||
let ephemeral_key = output.ephemeral_key();
|
||
let shared_secret = D::ka_agree_enc(&esk, &pk_d);
|
||
// The small-order point check at the point of output parsing rejects
|
||
// non-canonical encodings, so reencoding here for the KDF should
|
||
// be okay.
|
||
let key = D::kdf(shared_secret, &ephemeral_key);
|
||
|
||
let mut plaintext = NotePlaintextBytes([0; NOTE_PLAINTEXT_SIZE]);
|
||
plaintext
|
||
.0
|
||
.copy_from_slice(&enc_ciphertext[..NOTE_PLAINTEXT_SIZE]);
|
||
|
||
ChaCha20Poly1305::new(key.as_ref().into())
|
||
.decrypt_in_place_detached(
|
||
[0u8; 12][..].into(),
|
||
&[],
|
||
&mut plaintext.0,
|
||
enc_ciphertext[NOTE_PLAINTEXT_SIZE..].into(),
|
||
)
|
||
.ok()?;
|
||
|
||
let (note, to) = domain.parse_note_plaintext_without_memo_ovk(&pk_d, &plaintext)?;
|
||
let memo = domain.extract_memo(&plaintext);
|
||
|
||
// ZIP 212: Check that the esk provided to this function is consistent with the esk we can
|
||
// derive from the note. This check corresponds to `ToScalar(PRF^{expand}_{rseed}([4]) = esk`
|
||
// in https://zips.z.cash/protocol/protocol.pdf#decryptovk. (`ρ^opt = []` for Sapling.)
|
||
if let Some(derived_esk) = D::derive_esk(¬e) {
|
||
if (!derived_esk.ct_eq(&esk)).into() {
|
||
return None;
|
||
}
|
||
}
|
||
|
||
if let NoteValidity::Valid =
|
||
check_note_validity::<D>(¬e, &ephemeral_key, &output.cmstar_bytes())
|
||
{
|
||
Some((note, to, memo))
|
||
} else {
|
||
None
|
||
}
|
||
}
|