From 7e67014042cfcc6699480ef600d62b54b644733b Mon Sep 17 00:00:00 2001
From: Giacomo Pasini <21265557+zeegomo@users.noreply.github.com>
Date: Thu, 1 Aug 2024 12:46:17 +0200
Subject: [PATCH] Deposit (#8)

* Add native zone deposits

* check note unit and death constraints

* fix deposit logic

* fix ptx merkle root derivation

* restrict ptx inputs/outputs

* re-org directories
---
 goas/cl/cl/src/balance.rs                     |  15 +-
 goas/cl/cl/src/note.rs                        |  10 +-
 goas/cl/cl/src/nullifier.rs                   |   4 +
 goas/cl/cl/src/partial_tx.rs                  |   4 +-
 goas/zone/Cargo.toml                          |   2 +-
 goas/zone/common/Cargo.toml                   |   4 +-
 goas/zone/common/src/lib.rs                   |  60 +++++---
 goas/zone/{host => executor}/Cargo.toml       |   2 +-
 .../{host => executor}/src/bin/groth16.rs     |   0
 goas/zone/{host => executor}/src/main.rs      |   4 +-
 goas/zone/methods/Cargo.toml                  |  10 --
 goas/zone/methods/build.rs                    |   3 -
 goas/zone/methods/guest/src/main.rs           |  40 -----
 goas/zone/methods/src/lib.rs                  |   1 -
 goas/zone/proof_statements/src/zone_funds.rs  |   1 -
 goas/zone/risc0_proofs/Cargo.toml             |   2 +-
 .../risc0_proofs/spend_zone_funds/src/main.rs |  10 +-
 .../zone_state}/Cargo.toml                    |   6 +-
 goas/zone/risc0_proofs/zone_state/src/main.rs | 140 ++++++++++++++++++
 19 files changed, 216 insertions(+), 102 deletions(-)
 rename goas/zone/{host => executor}/Cargo.toml (84%)
 rename goas/zone/{host => executor}/src/bin/groth16.rs (100%)
 rename goas/zone/{host => executor}/src/main.rs (93%)
 delete mode 100644 goas/zone/methods/Cargo.toml
 delete mode 100644 goas/zone/methods/build.rs
 delete mode 100644 goas/zone/methods/guest/src/main.rs
 delete mode 100644 goas/zone/methods/src/lib.rs
 rename goas/zone/{methods/guest => risc0_proofs/zone_state}/Cargo.toml (85%)
 create mode 100644 goas/zone/risc0_proofs/zone_state/src/main.rs

diff --git a/goas/cl/cl/src/balance.rs b/goas/cl/cl/src/balance.rs
index b49f18b..416a103 100644
--- a/goas/cl/cl/src/balance.rs
+++ b/goas/cl/cl/src/balance.rs
@@ -13,17 +13,20 @@ lazy_static! {
 #[derive(Debug, PartialEq, Eq, Clone, Copy, Serialize, Deserialize)]
 pub struct Balance(pub RistrettoPoint);
 
+pub type Value = u64;
+pub type Unit = RistrettoPoint;
+
 #[derive(Debug, PartialEq, Eq, Clone, Copy, Serialize, Deserialize)]
 pub struct BalanceWitness(pub Scalar);
 
 impl Balance {
     /// A commitment to zero, blinded by the provided balance witness
     pub fn zero(blinding: BalanceWitness) -> Self {
-	// Since, balance commitments are `value * UnitPoint + blinding * H`, when value=0, the commmitment is unitless.
-	// So we use the generator point as a stand in for the unit point.
-	//
-	// TAI: we can optimize this further from `0*G + r*H` to just `r*H` to save a point scalar mult + point addition.
-	let unit = curve25519_dalek::constants::RISTRETTO_BASEPOINT_POINT;
+        // Since, balance commitments are `value * UnitPoint + blinding * H`, when value=0, the commmitment is unitless.
+        // So we use the generator point as a stand in for the unit point.
+        //
+        // TAI: we can optimize this further from `0*G + r*H` to just `r*H` to save a point scalar mult + point addition.
+        let unit = curve25519_dalek::constants::RISTRETTO_BASEPOINT_POINT;
         Self(balance(0, unit, blinding.0))
     }
 
@@ -46,7 +49,7 @@ impl BalanceWitness {
     }
 }
 
-pub fn balance(value: u64, unit: RistrettoPoint, blinding: Scalar) -> RistrettoPoint {
+pub fn balance(value: u64, unit: Unit, blinding: Scalar) -> Unit {
     let value_scalar = Scalar::from(value);
     // can vartime leak the number of cycles through the stark proof?
     RistrettoPoint::vartime_multiscalar_mul(
diff --git a/goas/cl/cl/src/note.rs b/goas/cl/cl/src/note.rs
index 10a773e..644744c 100644
--- a/goas/cl/cl/src/note.rs
+++ b/goas/cl/cl/src/note.rs
@@ -1,8 +1,10 @@
-use curve25519_dalek::RistrettoPoint;
 use serde::{Deserialize, Serialize};
 use sha2::{Digest, Sha256};
 
-use crate::nullifier::{NullifierCommitment, NullifierNonce};
+use crate::{
+    balance::Unit,
+    nullifier::{NullifierCommitment, NullifierNonce},
+};
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize, Deserialize)]
 pub struct DeathCommitment(pub [u8; 32]);
@@ -16,7 +18,7 @@ pub fn death_commitment(death_constraint: &[u8]) -> DeathCommitment {
     DeathCommitment(death_cm)
 }
 
-pub fn unit_point(unit: &str) -> RistrettoPoint {
+pub fn unit_point(unit: &str) -> Unit {
     crate::crypto::hash_to_curve(unit.as_bytes())
 }
 
@@ -34,7 +36,7 @@ impl NoteCommitment {
 #[derive(Debug, PartialEq, Eq, Clone, Copy, Serialize, Deserialize)]
 pub struct NoteWitness {
     pub value: u64,
-    pub unit: RistrettoPoint,
+    pub unit: Unit,
     pub death_constraint: [u8; 32], // death constraint verification key
     pub state: [u8; 32],
 }
diff --git a/goas/cl/cl/src/nullifier.rs b/goas/cl/cl/src/nullifier.rs
index 84189a1..d5fb406 100644
--- a/goas/cl/cl/src/nullifier.rs
+++ b/goas/cl/cl/src/nullifier.rs
@@ -65,6 +65,10 @@ impl NullifierCommitment {
     pub fn hex(&self) -> String {
         hex::encode(self.0)
     }
+
+    pub const fn from_bytes(bytes: [u8; 32]) -> Self {
+        Self(bytes)
+    }
 }
 
 impl NullifierNonce {
diff --git a/goas/cl/cl/src/partial_tx.rs b/goas/cl/cl/src/partial_tx.rs
index afe9785..5610421 100644
--- a/goas/cl/cl/src/partial_tx.rs
+++ b/goas/cl/cl/src/partial_tx.rs
@@ -8,8 +8,8 @@ use crate::input::{Input, InputWitness};
 use crate::merkle;
 use crate::output::{Output, OutputWitness};
 
-const MAX_INPUTS: usize = 8;
-const MAX_OUTPUTS: usize = 8;
+pub const MAX_INPUTS: usize = 8;
+pub const MAX_OUTPUTS: usize = 8;
 
 /// The partial transaction commitment couples an input to a partial transaction.
 /// Prevents partial tx unbundling.
diff --git a/goas/zone/Cargo.toml b/goas/zone/Cargo.toml
index b8dd50d..7cc3b61 100644
--- a/goas/zone/Cargo.toml
+++ b/goas/zone/Cargo.toml
@@ -1,6 +1,6 @@
 [workspace]
 resolver = "2"
-members = [ "common","host", "methods", "proof_statements", "risc0_proofs"]
+members = [ "common", "executor", "proof_statements", "risc0_proofs"]
 
 # Always optimize; building and running the guest takes much longer without optimization.
 [profile.dev]
diff --git a/goas/zone/common/Cargo.toml b/goas/zone/common/Cargo.toml
index 921f2c8..3fdc733 100644
--- a/goas/zone/common/Cargo.toml
+++ b/goas/zone/common/Cargo.toml
@@ -6,4 +6,6 @@ edition = "2021"
 [dependencies]
 serde = { version = "1", features = ["derive"] }
 cl = { path = "../../cl/cl" }
-proof_statements = { path = "../proof_statements", package = "goas_proof_statements" }
\ No newline at end of file
+goas_proof_statements = { path = "../proof_statements" }
+proof_statements = { path = "../../cl/proof_statements" }
+once_cell = "1"
\ No newline at end of file
diff --git a/goas/zone/common/src/lib.rs b/goas/zone/common/src/lib.rs
index cca9cdc..88cc84b 100644
--- a/goas/zone/common/src/lib.rs
+++ b/goas/zone/common/src/lib.rs
@@ -1,4 +1,11 @@
-use cl::nullifier::{Nullifier, NullifierCommitment};
+use cl::{
+    balance::Unit,
+    crypto,
+    input::InputWitness,
+    nullifier::{Nullifier, NullifierCommitment},
+    output::OutputWitness,
+};
+use once_cell::sync::Lazy;
 use serde::{Deserialize, Serialize};
 use std::collections::BTreeMap;
 
@@ -11,6 +18,17 @@ pub const MAX_EVENTS: usize = 1 << 8;
 #[derive(Clone, Copy, Serialize, Deserialize)]
 pub struct StateCommitment([u8; 32]);
 
+pub type AccountId = u32;
+
+// PLACEHOLDER: replace with the death constraint vk of the zone funds
+pub const ZONE_FUNDS_VK: [u8; 32] = [0; 32];
+// PLACEHOLDER: this is probably going to be NMO?
+pub static ZONE_CL_FUNDS_UNIT: Lazy<Unit> = Lazy::new(|| crypto::hash_to_curve(b"NMO"));
+// PLACEHOLDER
+pub static ZONE_UNIT: Lazy<Unit> = Lazy::new(|| crypto::hash_to_curve(b"ZONE_UNIT"));
+// PLACEHOLDER
+pub const ZONE_NF_PK: NullifierCommitment = NullifierCommitment::from_bytes([0; 32]);
+
 #[derive(Clone, Serialize, Deserialize)]
 pub struct StateWitness {
     pub balances: BTreeMap<u32, u32>,
@@ -38,12 +56,8 @@ impl StateWitness {
     }
 
     fn included_txs_root(&self) -> [u8; 32] {
-        let tx_bytes = Vec::from_iter(
-            self.included_txs
-                .iter()
-                .map(Input::to_bytes)
-                .map(Vec::from_iter),
-        );
+        // this is a placeholder
+        let tx_bytes = [vec![0u8; 32]];
         let tx_merkle_leaves = cl::merkle::padded_leaves(&tx_bytes);
         cl::merkle::root::<MAX_TXS>(tx_merkle_leaves)
     }
@@ -62,8 +76,8 @@ impl StateWitness {
 
 #[derive(Debug, Clone, Copy, Serialize, Deserialize)]
 pub struct Withdraw {
-    pub from: u32,
-    pub amount: u32,
+    pub from: AccountId,
+    pub amount: AccountId,
     pub to: NullifierCommitment,
     pub nf: Nullifier,
 }
@@ -79,22 +93,30 @@ impl Withdraw {
     }
 }
 
-#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
-pub enum Input {
-    Withdraw(Withdraw),
+/// A deposit of funds into the zone
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct Deposit {
+    /// The note that is used to deposit funds into the zone
+    pub deposit: InputWitness,
+
+    // This zone state note
+    pub zone_note_in: InputWitness,
+    pub zone_note_out: OutputWitness,
+
+    // The zone funds note
+    pub zone_funds_in: InputWitness,
+    pub zone_funds_out: OutputWitness,
 }
 
-impl Input {
-    pub fn to_bytes(&self) -> Vec<u8> {
-        match self {
-            Input::Withdraw(withdraw) => withdraw.to_bytes().to_vec(),
-        }
-    }
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub enum Input {
+    Withdraw(Withdraw),
+    Deposit(Deposit),
 }
 
 #[derive(Debug, Clone, Copy, Serialize, Deserialize)]
 pub enum Event {
-    Spend(proof_statements::zone_funds::Spend),
+    Spend(goas_proof_statements::zone_funds::Spend),
 }
 
 impl Event {
diff --git a/goas/zone/host/Cargo.toml b/goas/zone/executor/Cargo.toml
similarity index 84%
rename from goas/zone/host/Cargo.toml
rename to goas/zone/executor/Cargo.toml
index 2864725..47ce798 100644
--- a/goas/zone/host/Cargo.toml
+++ b/goas/zone/executor/Cargo.toml
@@ -5,7 +5,7 @@ edition = "2021"
 default-run = "host"
 
 [dependencies]
-methods = { path = "../methods" }
+goas_risc0_proofs = { path = "../risc0_proofs", package = "goas_risc0_proofs" }
 risc0-zkvm = { version = "1.0", features = ["prove", "metal"] }
 risc0-groth16 = { version = "1.0" }
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }
diff --git a/goas/zone/host/src/bin/groth16.rs b/goas/zone/executor/src/bin/groth16.rs
similarity index 100%
rename from goas/zone/host/src/bin/groth16.rs
rename to goas/zone/executor/src/bin/groth16.rs
diff --git a/goas/zone/host/src/main.rs b/goas/zone/executor/src/main.rs
similarity index 93%
rename from goas/zone/host/src/main.rs
rename to goas/zone/executor/src/main.rs
index 17cd386..90a68fe 100644
--- a/goas/zone/host/src/main.rs
+++ b/goas/zone/executor/src/main.rs
@@ -36,7 +36,7 @@ fn stf_prove_stark(state: StateWitness, inputs: Vec<Input>) {
     // This struct contains the receipt along with statistics about execution of the guest
     let opts = risc0_zkvm::ProverOpts::succinct();
     let prove_info = prover
-        .prove_with_opts(env, methods::METHOD_ELF, &opts)
+        .prove_with_opts(env, goas_risc0_proofs::ZONE_STATE_ELF, &opts)
         .unwrap();
 
     println!("STARK prover time: {:.2?}", start_t.elapsed());
@@ -48,7 +48,7 @@ fn stf_prove_stark(state: StateWitness, inputs: Vec<Input>) {
     std::fs::write("proof.stark", bincode::serialize(&receipt).unwrap()).unwrap();
     // The receipt was verified at the end of proving, but the below code is an
     // example of how someone else could verify this receipt.
-    receipt.verify(methods::METHOD_ID).unwrap();
+    receipt.verify(goas_risc0_proofs::ZONE_STATE_ID).unwrap();
 }
 
 fn main() {
diff --git a/goas/zone/methods/Cargo.toml b/goas/zone/methods/Cargo.toml
deleted file mode 100644
index 0a943cf..0000000
--- a/goas/zone/methods/Cargo.toml
+++ /dev/null
@@ -1,10 +0,0 @@
-[package]
-name = "methods"
-version = "0.1.0"
-edition = "2021"
-
-[build-dependencies]
-risc0-build = { version = "1.0" }
-
-[package.metadata.risc0]
-methods = ["guest"]
diff --git a/goas/zone/methods/build.rs b/goas/zone/methods/build.rs
deleted file mode 100644
index 08a8a4e..0000000
--- a/goas/zone/methods/build.rs
+++ /dev/null
@@ -1,3 +0,0 @@
-fn main() {
-    risc0_build::embed_methods();
-}
diff --git a/goas/zone/methods/guest/src/main.rs b/goas/zone/methods/guest/src/main.rs
deleted file mode 100644
index ae9483f..0000000
--- a/goas/zone/methods/guest/src/main.rs
+++ /dev/null
@@ -1,40 +0,0 @@
-use common::*;
-use proof_statements::zone_funds::Spend;
-use risc0_zkvm::guest::env;
-
-fn withdraw(mut state: StateWitness, withdraw: Withdraw) -> StateWitness {
-    state.included_txs.push(Input::Withdraw(withdraw));
-
-    let Withdraw {
-        from,
-        amount,
-        to,
-        nf,
-    } = withdraw;
-
-    let from_balance = state.balances.entry(from).or_insert(0);
-    *from_balance = from.checked_sub(amount).expect("insufficient funds in account");
-    let spend_auth = Spend {
-        amount: amount.into(),
-        to,
-        nf,
-    };
-
-    state.output_events.push(Event::Spend(spend_auth));
-    state
-}
-
-fn main() {
-    let inputs: Vec<Input> = env::read();
-    let mut state: StateWitness = env::read();
-
-    for input in inputs {
-        match input {
-            Input::Withdraw(input) => {
-                state = withdraw(state, input);
-            }
-        }
-    }
-
-    env::commit(&state.commit());
-}
diff --git a/goas/zone/methods/src/lib.rs b/goas/zone/methods/src/lib.rs
deleted file mode 100644
index 1bdb308..0000000
--- a/goas/zone/methods/src/lib.rs
+++ /dev/null
@@ -1 +0,0 @@
-include!(concat!(env!("OUT_DIR"), "/methods.rs"));
diff --git a/goas/zone/proof_statements/src/zone_funds.rs b/goas/zone/proof_statements/src/zone_funds.rs
index 5da4346..c44d8db 100644
--- a/goas/zone/proof_statements/src/zone_funds.rs
+++ b/goas/zone/proof_statements/src/zone_funds.rs
@@ -22,7 +22,6 @@ impl Spend {
     }
 }
 
-/// There are two kind of paths
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub struct SpendFundsPrivate {
     /// The note we're spending
diff --git a/goas/zone/risc0_proofs/Cargo.toml b/goas/zone/risc0_proofs/Cargo.toml
index e73bbbb..e7446b1 100644
--- a/goas/zone/risc0_proofs/Cargo.toml
+++ b/goas/zone/risc0_proofs/Cargo.toml
@@ -7,5 +7,5 @@ edition = "2021"
 risc0-build = { version = "1.0" }
 
 [package.metadata.risc0]
-methods = ["spend_zone_funds"]
+methods = ["spend_zone_funds", "zone_state"]
 
diff --git a/goas/zone/risc0_proofs/spend_zone_funds/src/main.rs b/goas/zone/risc0_proofs/spend_zone_funds/src/main.rs
index 7510e03..42f7f51 100644
--- a/goas/zone/risc0_proofs/spend_zone_funds/src/main.rs
+++ b/goas/zone/risc0_proofs/spend_zone_funds/src/main.rs
@@ -60,12 +60,9 @@ fn main() {
         out_zone_funds.output.balance_blinding,
         in_zone_funds.input.balance_blinding
     );
-    let mut evolved_nonce = [0; 16];
-    evolved_nonce[..16]
-        .copy_from_slice(&Sha256::digest(&out_zone_funds.output.nonce.as_bytes())[..16]);
     assert_eq!(
         out_zone_funds.output.nonce,
-        NullifierNonce::from_bytes(evolved_nonce)
+        NullifierNonce::from_bytes(Sha256::digest(&out_zone_funds.output.nonce.as_bytes()).into())
     );
 
     assert_eq!(ptx_root, spent_note.ptx_root());
@@ -76,8 +73,5 @@ fn main() {
     // check the correct recipient is being paid
     assert_eq!(spent_note.output.nf_pk, spend_event.to);
 
-    env::commit(&DeathConstraintPublic {
-        ptx_root,
-        nf,
-    });
+    env::commit(&DeathConstraintPublic { ptx_root, nf });
 }
diff --git a/goas/zone/methods/guest/Cargo.toml b/goas/zone/risc0_proofs/zone_state/Cargo.toml
similarity index 85%
rename from goas/zone/methods/guest/Cargo.toml
rename to goas/zone/risc0_proofs/zone_state/Cargo.toml
index 9c7aea4..ec3f512 100644
--- a/goas/zone/methods/guest/Cargo.toml
+++ b/goas/zone/risc0_proofs/zone_state/Cargo.toml
@@ -1,7 +1,7 @@
 
 
 [package]
-name = "method"
+name = "zone_state"
 version = "0.1.0"
 edition = "2021"
 
@@ -14,7 +14,9 @@ serde = { version = "1.0", features = ["derive"] }
 bincode = "1"
 common = { path = "../../common" }
 cl = { path = "../../../cl/cl" }
-proof_statements = { path = "../../proof_statements", package = "goas_proof_statements" }
+goas_proof_statements = { path = "../../proof_statements" }
+proof_statements = { path = "../../../cl/proof_statements" }
+sha2 = "0.10"
 
 [patch.crates-io]
 # Placing these patch statement in the workspace Cargo.toml will add RISC Zero SHA-256 and bigint
diff --git a/goas/zone/risc0_proofs/zone_state/src/main.rs b/goas/zone/risc0_proofs/zone_state/src/main.rs
new file mode 100644
index 0000000..972196c
--- /dev/null
+++ b/goas/zone/risc0_proofs/zone_state/src/main.rs
@@ -0,0 +1,140 @@
+use cl::{
+    merkle,
+    nullifier::{Nullifier, NullifierNonce, NullifierSecret},
+    partial_tx::{MAX_INPUTS, MAX_OUTPUTS},
+    PtxRoot,
+};
+
+use common::*;
+use goas_proof_statements::zone_funds::Spend;
+use proof_statements::death_constraint::DeathConstraintPublic;
+use risc0_zkvm::guest::env;
+use sha2::{Digest, Sha256};
+
+fn withdraw(mut state: StateWitness, withdraw: Withdraw) -> StateWitness {
+    state.included_txs.push(Input::Withdraw(withdraw));
+
+    let Withdraw {
+        from,
+        amount,
+        to,
+        nf,
+    } = withdraw;
+
+    let from_balance = state.balances.entry(from).or_insert(0);
+    *from_balance = from
+        .checked_sub(amount)
+        .expect("insufficient funds in account");
+    let spend_auth = Spend {
+        amount: amount.into(),
+        to,
+        nf,
+    };
+
+    state.output_events.push(Event::Spend(spend_auth));
+    state
+}
+
+fn deposit(
+    mut state: StateWitness,
+    deposit: Deposit,
+    pub_inputs: DeathConstraintPublic,
+) -> StateWitness {
+    state.included_txs.push(Input::Deposit(deposit.clone()));
+
+    let Deposit {
+        deposit,
+        zone_note_in,
+        zone_note_out,
+        zone_funds_in,
+        zone_funds_out,
+    } = deposit;
+
+    // 1) Check there are no more input/output notes than expected
+    let inputs = [
+        deposit.commit().to_bytes().to_vec(),
+        zone_note_in.commit().to_bytes().to_vec(),
+        zone_funds_in.commit().to_bytes().to_vec(),
+    ];
+
+    let inputs_root = merkle::root(merkle::padded_leaves::<MAX_INPUTS>(&inputs));
+
+    let outputs = [
+        zone_note_out.commit().to_bytes().to_vec(),
+        zone_funds_out.commit().to_bytes().to_vec(),
+    ];
+
+    let outputs_root = merkle::root(merkle::padded_leaves::<MAX_OUTPUTS>(&outputs));
+
+    let ptx_root = PtxRoot(merkle::node(inputs_root, outputs_root));
+    assert_eq!(ptx_root, pub_inputs.ptx_root);
+
+    // 2) Check the deposit note is not already under control of the zone
+    assert_ne!(deposit.note.death_constraint, ZONE_FUNDS_VK);
+
+    // 3) Check the ptx is balanced. This is not a requirement for standard ptxs, but we need it
+    //    in deposits (at least in a first version) to ensure fund tracking
+    assert_eq!(deposit.note.unit, *ZONE_UNIT);
+    assert_eq!(zone_funds_in.note.unit, *ZONE_UNIT);
+    assert_eq!(zone_funds_out.note.unit, *ZONE_UNIT);
+
+    let in_sum = deposit.note.value + zone_funds_in.note.value;
+
+    let out_sum = zone_note_out.note.value;
+
+    assert_eq!(out_sum, in_sum, "deposit ptx is unbalanced");
+
+    // 4) Check the zone fund notes are correctly created
+    assert_eq!(zone_funds_in.note.death_constraint, ZONE_FUNDS_VK);
+    assert_eq!(zone_funds_out.note.death_constraint, ZONE_FUNDS_VK);
+    assert_eq!(zone_funds_in.nf_sk, NullifierSecret::from_bytes([0; 16])); // there is no secret in the zone funds
+    assert_eq!(zone_funds_out.nf_pk, zone_funds_in.nf_sk.commit()); // the sk is the same
+                                                                    // nonce is correctly evolved
+    assert_eq!(
+        zone_funds_out.nonce,
+        NullifierNonce::from_bytes(Sha256::digest(&zone_funds_in.nonce.as_bytes()).into())
+    );
+
+    // 5) Check zone state notes are correctly created
+    assert_eq!(
+        zone_note_in.note.death_constraint,
+        zone_note_out.note.death_constraint
+    );
+    assert_eq!(zone_note_in.nf_sk, NullifierSecret::from_bytes([0; 16])); //// there is no secret in the zone state
+    assert_eq!(zone_note_out.nf_pk, zone_note_in.nf_sk.commit()); // the sk is the same
+    assert_eq!(zone_note_in.note.unit, zone_note_out.note.unit);
+    assert_eq!(zone_note_in.note.value, zone_note_out.note.value);
+    // nonce is correctly evolved
+    assert_eq!(
+        zone_note_out.nonce,
+        NullifierNonce::from_bytes(Sha256::digest(&zone_note_in.nonce.as_bytes()).into())
+    );
+    let nullifier = Nullifier::new(zone_note_in.nf_sk, zone_note_in.nonce);
+    assert_eq!(nullifier, pub_inputs.nf);
+
+    // 6) We're now ready to do the deposit!
+    let amount = deposit.note.value as u32;
+    let to = AccountId::from_be_bytes(<[u8; 4]>::try_from(&deposit.note.state[0..4]).unwrap());
+
+    let to_balance = state.balances.entry(to).or_insert(0);
+    *to_balance = to_balance
+        .checked_add(amount)
+        .expect("overflow when depositing");
+
+    state
+}
+
+fn main() {
+    let public_inputs: DeathConstraintPublic = env::read();
+    let inputs: Vec<Input> = env::read();
+    let mut state: StateWitness = env::read();
+
+    for input in inputs {
+        match input {
+            Input::Withdraw(input) => state = withdraw(state, input),
+            Input::Deposit(input) => state = deposit(state, input, public_inputs),
+        }
+    }
+
+    env::commit(&state.commit());
+}