zakura-sapling-crypto 1.0.0

//! PCZT support for Sapling.

use alloc::collections::BTreeMap;
use alloc::string::String;
use alloc::vec::Vec;
use core::fmt;

use getset::Getters;
use redjubjub::{Binding, SpendAuth};
use zcash_note_encryption::{
    ENC_CIPHERTEXT_SIZE, EphemeralKeyBytes, OUT_CIPHERTEXT_SIZE, OutgoingCipherKey,
};
use zip32::ChildIndex;

use crate::{
    Anchor, MerklePath, Nullifier, PaymentAddress, ProofGenerationKey, Rseed,
    bundle::GrothProofBytes,
    keys::SpendAuthorizingKey,
    note::ExtractedNoteCommitment,
    value::{NoteValue, ValueCommitTrapdoor, ValueCommitment, ValueSum},
};

mod parse;
pub use parse::ParseError;

mod verify;
pub use verify::VerifyError;

mod io_finalizer;
pub use io_finalizer::IoFinalizerError;

mod updater;
pub use updater::{OutputUpdater, SpendUpdater, Updater, UpdaterError};

#[cfg(feature = "circuit")]
mod prover;
#[cfg(feature = "circuit")]
pub use prover::ProverError;

mod signer;
pub use signer::SignerError;

mod tx_extractor;
pub use tx_extractor::{TxExtractorError, Unbound};

/// PCZT fields that are specific to producing the transaction's Sapling bundle (if any).
///
/// This struct is for representing Sapling in a partially-created transaction. If you
/// have a fully-created transaction, use [the regular `Bundle` struct].
///
/// [the regular `Bundle` struct]: crate::Bundle
#[derive(Debug, Getters)]
#[getset(get = "pub")]
pub struct Bundle {
    /// The Sapling spends in this bundle.
    ///
    /// Entries are added by the Constructor, and modified by an Updater, IO Finalizer,
    /// Prover, Signer, Combiner, or Spend Finalizer.
    pub(crate) spends: Vec<Spend>,

    /// The Sapling outputs in this bundle.
    ///
    /// Entries are added by the Constructor, and modified by an Updater, IO Finalizer,
    /// Prover, Signer, Combiner, or Spend Finalizer.
    pub(crate) outputs: Vec<Output>,

    /// The net value of Sapling `spends` minus `outputs`.
    ///
    /// This is initialized by the Creator, and updated by the Constructor as spends or
    /// outputs are added to the PCZT. It enables per-spend and per-output values to be
    /// redacted from the PCZT after they are no longer necessary.
    pub(crate) value_sum: ValueSum,

    /// The Sapling anchor for this transaction.
    ///
    /// Set by the Creator.
    pub(crate) anchor: Anchor,

    /// The Sapling binding signature signing key.
    ///
    /// - This is `None` until it is set by the IO Finalizer.
    /// - The Transaction Extractor uses this to produce the binding signature.
    pub(crate) bsk: Option<redjubjub::SigningKey<Binding>>,
}

impl Bundle {
    /// Returns a mutable reference to the spends in this bundle.
    ///
    /// This is used by Signers to apply signatures with [`Spend::sign`].
    pub fn spends_mut(&mut self) -> &mut [Spend] {
        &mut self.spends
    }
}

/// Information about a Sapling spend within a transaction.
///
/// This struct is for representing Sapling spends in a partially-created transaction. If
/// you have a fully-created transaction, use [the regular `SpendDescription` struct].
///
/// [the regular `SpendDescription` struct]: crate::bundle::SpendDescription
#[derive(Debug, Getters)]
#[getset(get = "pub")]
pub struct Spend {
    /// A commitment to the value consumed by this spend.
    pub(crate) cv: ValueCommitment,

    /// The nullifier of the note being spent.
    pub(crate) nullifier: Nullifier,

    /// The randomized verification key for the note being spent.
    pub(crate) rk: redjubjub::VerificationKey<SpendAuth>,

    /// The Spend proof.
    ///
    /// This is set by the Prover.
    pub(crate) zkproof: Option<GrothProofBytes>,

    /// The spend authorization signature.
    ///
    /// This is set by the Signer.
    pub(crate) spend_auth_sig: Option<redjubjub::Signature<SpendAuth>>,

    /// The address that received the note being spent.
    ///
    /// - This is set by the Constructor (or Updater?).
    /// - This is required by the Prover.
    pub(crate) recipient: Option<PaymentAddress>,

    /// The value of the input being spent.
    ///
    /// This may be used by Signers to verify that the value matches `cv`, and to confirm
    /// the values and change involved in the transaction.
    ///
    /// This exposes the input value to all participants. For Signers who don't need this
    /// information, or after signatures have been applied, this can be redacted.
    pub(crate) value: Option<NoteValue>,

    /// The seed randomness for the note being spent.
    ///
    /// - This is set by the Constructor.
    /// - This is required by the Prover.
    pub(crate) rseed: Option<Rseed>,

    /// The value commitment randomness.
    ///
    /// - This is set by the Constructor.
    /// - The IO Finalizer compresses it into the `bsk`.
    /// - This is required by the Prover.
    /// - This may be used by Signers to verify that the value correctly matches `cv`.
    ///
    /// This opens `cv` for all participants. For Signers who don't need this information,
    /// or after proofs / signatures have been applied, this can be redacted.
    pub(crate) rcv: Option<ValueCommitTrapdoor>,

    /// The proof generation key `(ak, nsk)` corresponding to the recipient that received
    /// the note being spent.
    ///
    /// - This is set by the Updater.
    /// - This is required by the Prover.
    pub(crate) proof_generation_key: Option<ProofGenerationKey>,

    /// A witness from the note to the bundle's anchor.
    ///
    /// - This is set by the Updater.
    /// - This is required by the Prover.
    pub(crate) witness: Option<MerklePath>,

    /// The spend authorization randomizer.
    ///
    /// - This is chosen by the Constructor.
    /// - This is required by the Signer for creating `spend_auth_sig`, and may be used to
    ///   validate `rk`.
    /// - After`zkproof` / `spend_auth_sig` has been set, this can be redacted.
    pub(crate) alpha: Option<jubjub::Scalar>,

    /// The ZIP 32 derivation path at which the spending key can be found for the note
    /// being spent.
    pub(crate) zip32_derivation: Option<Zip32Derivation>,

    /// The spend authorizing key for this spent note, if it is a dummy note.
    ///
    /// - This is chosen by the Constructor.
    /// - This is required by the IO Finalizer, and is cleared by it once used.
    /// - Signers MUST reject PCZTs that contain `dummy_ask` values.
    pub(crate) dummy_ask: Option<SpendAuthorizingKey>,

    /// Proprietary fields related to the note being spent.
    pub(crate) proprietary: BTreeMap<String, Vec<u8>>,
}

/// Information about a Sapling output within a transaction.
///
/// This struct is for representing Sapling outputs in a partially-created transaction. If
/// you have a fully-created transaction, use [the regular `OutputDescription` struct].
///
/// [the regular `OutputDescription` struct]: crate::bundle::OutputDescription
#[derive(Getters)]
#[getset(get = "pub")]
pub struct Output {
    /// A commitment to the value created by this output.
    pub(crate) cv: ValueCommitment,

    /// A commitment to the new note being created.
    pub(crate) cmu: ExtractedNoteCommitment,

    /// The ephemeral key used to encrypt the note plaintext.
    pub(crate) ephemeral_key: EphemeralKeyBytes,

    /// The encrypted note plaintext for the output.
    ///
    /// Once we have memo bundles, we will be able to set memos independently of Outputs.
    /// For now, the Constructor sets both at the same time.
    pub(crate) enc_ciphertext: [u8; ENC_CIPHERTEXT_SIZE],

    /// The encrypted output plaintext for the output.
    pub(crate) out_ciphertext: [u8; OUT_CIPHERTEXT_SIZE],

    /// The Output proof.
    ///
    /// This is set by the Prover.
    pub(crate) zkproof: Option<GrothProofBytes>,

    /// The address that will receive the output.
    ///
    /// - This is set by the Constructor.
    /// - This is required by the Prover.
    /// - The Signer can use `recipient` and `rseed` (if present) to verify that
    ///   `enc_ciphertext` is correctly encrypted (and contains a note plaintext matching
    ///   the public commitments), and to confirm the value of the memo.
    pub(crate) recipient: Option<PaymentAddress>,

    /// The value of the output.
    ///
    /// This may be used by Signers to verify that the value matches `cv`, and to confirm
    /// the values and change involved in the transaction.
    ///
    /// This exposes the output value to all participants. For Signers who don't need this
    /// information, or after signatures have been applied, this can be redacted.
    pub(crate) value: Option<NoteValue>,

    /// The seed randomness for the output.
    ///
    /// - This is set by the Constructor.
    /// - This is required by the Prover.
    /// - The Signer can use `recipient` and `rseed` (if present) to verify that
    ///   `enc_ciphertext` is correctly encrypted (and contains a note plaintext matching
    ///   the public commitments), and to confirm the value of the memo.
    pub(crate) rseed: Option<[u8; 32]>,

    /// The value commitment randomness.
    ///
    /// - This is set by the Constructor.
    /// - The IO Finalizer compresses it into the bsk.
    /// - This is required by the Prover.
    /// - This may be used by Signers to verify that the value correctly matches `cv`.
    ///
    /// This opens `cv` for all participants. For Signers who don't need this information,
    /// or after proofs / signatures have been applied, this can be redacted.
    pub(crate) rcv: Option<ValueCommitTrapdoor>,

    /// The `ock` value used to encrypt `out_ciphertext`.
    ///
    /// This enables Signers to verify that `out_ciphertext` is correctly encrypted.
    ///
    /// This may be `None` if the Constructor added the output using an OVK policy of
    /// "None", to make the output unrecoverable from the chain by the sender.
    pub(crate) ock: Option<OutgoingCipherKey>,

    /// The ZIP 32 derivation path at which the spending key can be found for the output.
    pub(crate) zip32_derivation: Option<Zip32Derivation>,

    /// The user-facing address to which this output is being sent, if any.
    ///
    /// - This is set by an Updater.
    /// - Signers must parse this address (if present) and confirm that it contains
    ///   `recipient` (either directly, or e.g. as a receiver within a Unified Address).
    pub(crate) user_address: Option<String>,

    /// Proprietary fields related to the note being created.
    pub(crate) proprietary: BTreeMap<String, Vec<u8>>,
}

impl fmt::Debug for Output {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        f.debug_struct("Output")
            .field("cv", &self.cv)
            .field("cmu", &self.cmu)
            .field("ephemeral_key", &self.ephemeral_key)
            .field("enc_ciphertext", &self.enc_ciphertext)
            .field("out_ciphertext", &self.out_ciphertext)
            .field("zkproof", &self.zkproof)
            .field("recipient", &self.recipient)
            .field("value", &self.value)
            .field("rseed", &self.rseed)
            .field("rcv", &self.rcv)
            .field("zip32_derivation", &self.zip32_derivation)
            .field("user_address", &self.user_address)
            .field("proprietary", &self.proprietary)
            .finish_non_exhaustive()
    }
}

/// The ZIP 32 derivation path at which a key can be found.
#[derive(Debug, Getters, PartialEq, Eq)]
#[getset(get = "pub")]
pub struct Zip32Derivation {
    /// The [ZIP 32 seed fingerprint](https://zips.z.cash/zip-0032#seed-fingerprints).
    seed_fingerprint: [u8; 32],

    /// The sequence of indices corresponding to the shielded HD path.
    derivation_path: Vec<ChildIndex>,
}

impl Zip32Derivation {
    /// Extracts the ZIP 32 account index from this derivation path.
    ///
    /// Returns `None` if the seed fingerprints don't match, or if this is a non-standard
    /// derivation path.
    pub fn extract_account_index(
        &self,
        seed_fp: &zip32::fingerprint::SeedFingerprint,
        expected_coin_type: zip32::ChildIndex,
    ) -> Option<zip32::AccountId> {
        if self.seed_fingerprint == seed_fp.to_bytes() {
            match &self.derivation_path[..] {
                [purpose, coin_type, account_index]
                    if purpose == &zip32::ChildIndex::hardened(32)
                        && coin_type == &expected_coin_type =>
                {
                    Some(
                        zip32::AccountId::try_from(account_index.index() - (1 << 31))
                            .expect("zip32::ChildIndex only supports hardened"),
                    )
                }
                _ => None,
            }
        } else {
            None
        }
    }
}