zebra/zebra-consensus/src/transaction/check.rs

//! Transaction checks.
//!
//! Code in this file can freely assume that no pre-V4 transactions are present.

use std::{borrow::Cow, collections::HashSet, convert::TryFrom, hash::Hash};

use zebra_chain::{
    amount::{Amount, NonNegative},
    block::Height,
    orchard::Flags,
    parameters::{Network, NetworkUpgrade},
    sapling::{Output, PerSpendAnchor, Spend},
    transaction::Transaction,
};

use crate::error::TransactionError;

/// Checks that the transaction has inputs and outputs.
///
/// For `Transaction::V4`:
/// * At least one of `tx_in_count`, `nSpendsSapling`, and `nJoinSplit` MUST be non-zero.
/// * At least one of `tx_out_count`, `nOutputsSapling`, and `nJoinSplit` MUST be non-zero.
///
/// For `Transaction::V5`:
/// * This condition must hold: `tx_in_count` > 0 or `nSpendsSapling` > 0 or
/// (`nActionsOrchard` > 0 and `enableSpendsOrchard` = 1)
/// * This condition must hold: `tx_out_count` > 0 or `nOutputsSapling` > 0 or
/// (`nActionsOrchard` > 0 and `enableOutputsOrchard` = 1)
///
/// This check counts both `Coinbase` and `PrevOut` transparent inputs.
///
/// https://zips.z.cash/protocol/protocol.pdf#txnencodingandconsensus
pub fn has_inputs_and_outputs(tx: &Transaction) -> Result<(), TransactionError> {
    if !tx.has_transparent_or_shielded_inputs() {
        Err(TransactionError::NoInputs)
    } else if !tx.has_transparent_or_shielded_outputs() {
        Err(TransactionError::NoOutputs)
    } else {
        Ok(())
    }
}

/// Check that a coinbase transaction has no PrevOut inputs, JoinSplits, or spends.
///
/// A coinbase transaction MUST NOT have any transparent inputs, JoinSplit descriptions,
/// or Spend descriptions.
///
/// In a version 5 coinbase transaction, the enableSpendsOrchard flag MUST be 0.
///
/// This check only counts `PrevOut` transparent inputs.
///
/// https://zips.z.cash/protocol/protocol.pdf#txnencodingandconsensus
pub fn coinbase_tx_no_prevout_joinsplit_spend(tx: &Transaction) -> Result<(), TransactionError> {
    if tx.has_valid_coinbase_transaction_inputs() {
        if tx.contains_prevout_input() {
            return Err(TransactionError::CoinbaseHasPrevOutInput);
        } else if tx.joinsplit_count() > 0 {
            return Err(TransactionError::CoinbaseHasJoinSplit);
        } else if tx.sapling_spends_per_anchor().count() > 0 {
            return Err(TransactionError::CoinbaseHasSpend);
        }

        if let Some(orchard_shielded_data) = tx.orchard_shielded_data() {
            if orchard_shielded_data.flags.contains(Flags::ENABLE_SPENDS) {
                return Err(TransactionError::CoinbaseHasEnableSpendsOrchard);
            }
        }
    }

    Ok(())
}

/// Check that a Spend description's cv and rk are not of small order,
/// i.e. [h_J]cv MUST NOT be 𝒪_J and [h_J]rk MUST NOT be 𝒪_J.
///
/// https://zips.z.cash/protocol/protocol.pdf#spenddesc
pub fn spend_cv_rk_not_small_order(spend: &Spend<PerSpendAnchor>) -> Result<(), TransactionError> {
    if bool::from(spend.cv.0.is_small_order())
        || bool::from(
            jubjub::AffinePoint::from_bytes(spend.rk.into())
                .unwrap()
                .is_small_order(),
        )
    {
        Err(TransactionError::SmallOrder)
    } else {
        Ok(())
    }
}

/// Check that a Output description's cv and epk are not of small order,
/// i.e. [h_J]cv MUST NOT be 𝒪_J and [h_J]epk MUST NOT be 𝒪_J.
///
/// https://zips.z.cash/protocol/protocol.pdf#outputdesc
pub fn output_cv_epk_not_small_order(output: &Output) -> Result<(), TransactionError> {
    if bool::from(output.cv.0.is_small_order())
        || bool::from(
            jubjub::AffinePoint::from_bytes(output.ephemeral_key.into())
                .unwrap()
                .is_small_order(),
        )
    {
        Err(TransactionError::SmallOrder)
    } else {
        Ok(())
    }
}

/// Check if a transaction is adding to the sprout pool after Canopy
/// network upgrade given a block height and a network.
///
/// https://zips.z.cash/zip-0211
/// https://zips.z.cash/protocol/protocol.pdf#joinsplitdesc
pub fn disabled_add_to_sprout_pool(
    tx: &Transaction,
    height: Height,
    network: Network,
) -> Result<(), TransactionError> {
    let canopy_activation_height = NetworkUpgrade::Canopy
        .activation_height(network)
        .expect("Canopy activation height must be present for both networks");

    // [Canopy onward]: `vpub_old` MUST be zero.
    // https://zips.z.cash/protocol/protocol.pdf#joinsplitdesc
    if height >= canopy_activation_height {
        let zero = Amount::<NonNegative>::try_from(0).expect("an amount of 0 is always valid");

        let tx_sprout_pool = tx.output_values_to_sprout();
        for vpub_old in tx_sprout_pool {
            if *vpub_old != zero {
                return Err(TransactionError::DisabledAddToSproutPool);
            }
        }
    }

    Ok(())
}

/// Check if a transaction has any internal spend conflicts.
///
/// An internal spend conflict happens if the transaction spends a UTXO more than once or if it
/// reveals a nullifier more than once.
///
/// Consensus rules:
///
/// "each output of a particular transaction
/// can only be used as an input once in the block chain.
/// Any subsequent reference is a forbidden double spend-
/// an attempt to spend the same satoshis twice."
///
/// https://developer.bitcoin.org/devguide/block_chain.html#introduction
///
/// A _nullifier_ *MUST NOT* repeat either within a _transaction_, or across _transactions_ in a
/// _valid blockchain_ . *Sprout* and *Sapling* and *Orchard* _nulliers_ are considered disjoint,
/// even if they have the same bit pattern.
///
/// https://zips.z.cash/protocol/protocol.pdf#nullifierset
pub fn spend_conflicts(transaction: &Transaction) -> Result<(), TransactionError> {
    use crate::error::TransactionError::*;

    let transparent_outpoints = transaction.spent_outpoints().map(Cow::Owned);
    let sprout_nullifiers = transaction.sprout_nullifiers().map(Cow::Borrowed);
    let sapling_nullifiers = transaction.sapling_nullifiers().map(Cow::Borrowed);
    let orchard_nullifiers = transaction.orchard_nullifiers().map(Cow::Borrowed);

    check_for_duplicates(transparent_outpoints, DuplicateTransparentSpend)?;
    check_for_duplicates(sprout_nullifiers, DuplicateSproutNullifier)?;
    check_for_duplicates(sapling_nullifiers, DuplicateSaplingNullifier)?;
    check_for_duplicates(orchard_nullifiers, DuplicateOrchardNullifier)?;

    Ok(())
}

/// Check for duplicate items in a collection.
///
/// Each item should be wrapped by a [`Cow`] instance so that this helper function can properly
/// handle borrowed items and owned items.
///
/// If a duplicate is found, an error created by the `error_wrapper` is returned.
fn check_for_duplicates<'t, T>(
    items: impl IntoIterator<Item = Cow<'t, T>>,
    error_wrapper: impl FnOnce(T) -> TransactionError,
) -> Result<(), TransactionError>
where
    T: Clone + Eq + Hash + 't,
{
    let mut hash_set = HashSet::new();

    for item in items {
        if let Some(duplicate) = hash_set.replace(item) {
            return Err(error_wrapper(duplicate.into_owned()));
        }
    }

    Ok(())
}