consensus: add transaction::check module

zebra-consensus/src/transaction.rs

@@ -17,12 +17,15 @@ use zebra_chain::{
     parameters::NetworkUpgrade,
     primitives::{ed25519, redjubjub},
     transaction::{self, HashType, Transaction},
+    transparent::{self, Script},
 };
 
 use zebra_state as zs;
 
 use crate::{script, BoxError};
 
+mod check;
+
 /// Asynchronous transaction verification.
 #[derive(Debug, Clone)]
 pub struct Verifier<ZS> {
@@ -48,6 +51,8 @@ where
 pub enum VerifyTransactionError {
     /// Only V4 and later transactions can be verified.
     WrongVersion,
+    /// A transaction MUST move money around.
+    NoTransfer,
     /// Could not verify a transparent script
     Script(#[from] zebra_script::Error),
     /// Could not verify a Groth16 proof of a JoinSplit/Spend/Output description
@@ -154,13 +159,16 @@ where
                         }
                     }
 
+                    check::some_money_is_spent(&tx)?;
+                    check::any_coinbase_inputs_no_transparent_outputs(&tx)?;
+
                     let sighash = tx.sighash(
                         NetworkUpgrade::Sapling, // TODO: pass this in
                         HashType::ALL,           // TODO: check these
                         None,                    // TODO: check these
                     );
 
-                    if let Some(_joinsplit_data) = joinsplit_data {
+                    if let Some(joinsplit_data) = joinsplit_data {
                         // XXX create a method on JoinSplitData
                         // that prepares groth16::Items with the correct proofs
                         // and proof inputs, handling interstitial treestates
@@ -168,10 +176,7 @@ where
 
                         // Then, pass those items to self.joinsplit to verify them.
 
-                        // XXX refactor this into a nicely named check function
-                        // ed25519::VerificationKey::try_from(joinsplit_data.pub_key)
-                        //     .and_then(|vk| vk.verify(&joinsplit_data.sig, sighash))
-                        //     .map_err(VerifyTransactionError::Ed25519)
+                        check::validate_joinsplit_sig(joinsplit_data, sighash.as_bytes())?;
                     }
 
                     if let Some(shielded_data) = shielded_data {

zebra-consensus/src/transaction/check.rs

@@ -0,0 +1,78 @@
+use std::convert::TryFrom;
+
+use zebra_chain::{
+    amount::Amount,
+    primitives::{
+        ed25519,
+        redjubjub::{self, Binding},
+        Groth16Proof,
+    },
+    sapling::ValueCommitment,
+    transaction::{JoinSplitData, ShieldedData, Transaction},
+};
+
+use crate::transaction::VerifyTransactionError;
+
+/// Validate the JoinSplit binding signature.
+///
+/// https://zips.z.cash/protocol/canopy.pdf#sproutnonmalleability
+/// https://zips.z.cash/protocol/canopy.pdf#txnencodingandconsensus
+pub fn validate_joinsplit_sig(
+    joinsplit_data: &JoinSplitData<Groth16Proof>,
+    sighash: &[u8],
+) -> Result<(), VerifyTransactionError> {
+    ed25519::VerificationKey::try_from(joinsplit_data.pub_key)
+        .and_then(|vk| vk.verify(&joinsplit_data.sig, sighash))
+        .map_err(VerifyTransactionError::Ed25519)
+}
+
+/// Check that at least one of tx_in_count, nShieldedSpend, and nJoinSplit MUST
+/// be non-zero.
+///
+/// https://zips.z.cash/protocol/canopy.pdf#txnencodingandconsensus
+pub fn some_money_is_spent(tx: &Transaction) -> Result<(), VerifyTransactionError> {
+    match tx {
+        Transaction::V4 {
+            inputs,
+            joinsplit_data: Some(joinsplit_data),
+            shielded_data: Some(shielded_data),
+            ..
+        } => {
+            if inputs.len() > 0
+                || joinsplit_data.joinsplits().count() > 0
+                || shielded_data.spends().count() > 0
+            {
+                return Ok(());
+            } else {
+                return Err(VerifyTransactionError::NoTransfer);
+            }
+        }
+        _ => return Err(VerifyTransactionError::WrongVersion),
+    }
+}
+
+/// Check that a transaction with one or more transparent inputs from coinbase
+/// transactions has no transparent outputs.
+///
+/// Note that inputs from coinbase transactions include Founders’ Reward
+/// outputs.
+///
+/// https://zips.z.cash/protocol/canopy.pdf#consensusfrombitcoin
+pub fn any_coinbase_inputs_no_transparent_outputs(
+    tx: &Transaction,
+) -> Result<(), VerifyTransactionError> {
+    match tx {
+        Transaction::V4 {
+            inputs, outputs, ..
+        } => {
+            if !tx.contains_coinbase_input() {
+                return Ok(());
+            } else if outputs.len() == 0 {
+                return Ok(());
+            } else {
+                return Err(VerifyTransactionError::NoTransfer);
+            }
+        }
+        _ => return Err(VerifyTransactionError::WrongVersion),
+    }
+}