Implement persistent commitments (argumentcomputer#543)

* meta commit and hide

* progress on fetch

* resolve lifetime issue

* finish fetch

* improve Commitment implementations; open meta command that prints data

* add pub(crate)

* enclose non-wasm code in particular modules

* improved remarks on private data

* better generalizations in lurk_proof

* safer extraction of FieldData

* cleaner user feedback on fetch

* remove unnecessary allow(dead_code) flag

* clean up paths.rs

* review suggestions + revamp

* encoding proof claim as Lurk data

* clean up

* document field_data

* add tests for field_data

* change constructor names on Enum2 for a better POC test

* fix docstring for LurkProofMeta

Cargo.toml

@@ -47,6 +47,7 @@ rand_xorshift = "0.3.0"
 rayon = "1.7.0"
 rustyline-derive = "0.8.0"
 serde = { workspace = true, features = ["derive"] }
+serde_bytes = "0.11.12"
 serde_json = { workspace = true }
 serde_repr = "0.1.10"
 tap = "1.0.1"

fcomm/src/lib.rs

@@ -555,7 +555,7 @@ impl<F: LurkField + Serialize + DeserializeOwned> LurkPtr<F> {
             LurkPtr::ZStorePtr(z_store_ptr) => {
                 let z_store = &z_store_ptr.z_store;
                 let z_ptr = z_store_ptr.z_ptr;
-                s.intern_z_expr_ptr(z_ptr, z_store)
+                s.intern_z_expr_ptr(&z_ptr, z_store)
                     .expect("failed to intern z_ptr")
             }
         }

src/cli/commitment.rs

@@ -0,0 +1,50 @@
+use lurk::{field::LurkField, z_ptr::ZExprPtr, z_store::ZStore};
+use serde::{Deserialize, Serialize};
+
+use super::field_data::HasFieldModulus;
+
+/// Holds data for commitments.
+///
+/// **Warning**: holds private data. The `ZStore` contains the secret used to
+/// hide the original payload.
+#[derive(Serialize, Deserialize)]
+pub struct Commitment<F: LurkField> {
+    pub(crate) hidden: ZExprPtr<F>,
+    pub(crate) zstore: ZStore<F>,
+}
+
+impl<F: LurkField> HasFieldModulus for Commitment<F> {
+    fn field_modulus() -> String {
+        F::MODULUS.to_owned()
+    }
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+mod non_wasm {
+    use anyhow::Result;
+    use lurk::{field::LurkField, ptr::Ptr, store::Store, z_store::ZStore};
+    use serde::Serialize;
+
+    use crate::cli::{field_data::non_wasm::dump, paths::non_wasm::commitment_path};
+
+    use super::Commitment;
+
+    impl<F: LurkField> Commitment<F> {
+        pub fn new(secret: F, payload: Ptr<F>, store: &mut Store<F>) -> Result<Self> {
+            let hidden = store.hide(secret, payload);
+            let mut zstore = Some(ZStore::<F>::default());
+            let hidden = store.get_z_expr(&hidden, &mut zstore)?.0;
+            Ok(Self {
+                hidden,
+                zstore: zstore.unwrap(),
+            })
+        }
+    }
+
+    impl<F: LurkField + Serialize> Commitment<F> {
+        #[inline]
+        pub fn persist(self, hash: &str) -> Result<()> {
+            dump(self, commitment_path(hash))
+        }
+    }
+}

src/cli/field_data.rs

@@ -0,0 +1,169 @@
+use anyhow::Result;
+
+use serde::{de::DeserializeOwned, Deserialize, Serialize};
+
+// This module implements a 2-step serde protocol for data that is parametrized
+// on an arithmetic field in order to be properly deserialized.
+//
+// First, we serialize it to a vector of bytes. Then, we wrap the vector with a
+// struct that contains the field modulus, which, in turn, is serialized to the
+// final vector of bytes.
+//
+// When deserializing, we unwrap the vector of bytes and double check the field
+// modulus for consistency. If everything goes well, we further unwrap the second
+// vector of bytes.
+
+pub(crate) trait HasFieldModulus {
+    fn field_modulus() -> String;
+}
+
+#[allow(dead_code)]
+pub(crate) fn ser<T: Serialize + HasFieldModulus>(t: T) -> Result<Vec<u8>> {
+    Ok(bincode::serialize(&FieldData(t))?)
+}
+
+#[allow(dead_code)]
+pub(crate) fn de<T: DeserializeOwned + HasFieldModulus>(bytes: &[u8]) -> Result<T> {
+    let FieldData(data) = bincode::deserialize(bytes)?;
+    Ok(data)
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+pub mod non_wasm {
+    use super::{de, ser, HasFieldModulus};
+    use anyhow::Result;
+    use serde::{de::DeserializeOwned, Serialize};
+    use std::path::PathBuf;
+
+    pub(crate) fn dump<T: Serialize + HasFieldModulus>(t: T, path: PathBuf) -> Result<()> {
+        Ok(std::fs::write(path, ser(t)?)?)
+    }
+
+    pub(crate) fn load<T: DeserializeOwned + HasFieldModulus>(path: PathBuf) -> Result<T> {
+        de(&std::fs::read(path)?)
+    }
+}
+
+#[derive(Debug, PartialEq, Eq)]
+struct FieldData<T>(T);
+
+#[derive(Deserialize, Serialize)]
+struct FieldDataWrap {
+    field_modulus: String,
+    #[serde(with = "serde_bytes")]
+    bytes: Vec<u8>,
+}
+
+impl<'de, T: DeserializeOwned + HasFieldModulus> Deserialize<'de> for FieldData<T> {
+    fn deserialize<D>(deserializer: D) -> std::result::Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        let fdw = FieldDataWrap::deserialize(deserializer)?;
+        if fdw.field_modulus != T::field_modulus() {
+            return Err(serde::de::Error::custom("Field mismatch"));
+        };
+        let t: T = bincode::deserialize(&fdw.bytes).map_err(serde::de::Error::custom)?;
+        Ok(FieldData(t))
+    }
+}
+
+impl<T: Serialize + HasFieldModulus> Serialize for FieldData<T> {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        let fdw = FieldDataWrap {
+            field_modulus: T::field_modulus(),
+            bytes: bincode::serialize(&self.0).map_err(serde::ser::Error::custom)?,
+        };
+        fdw.serialize(serializer)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use ff::Field;
+    use lurk::field::LurkField;
+    use pasta_curves::Fq;
+    use serde::{Deserialize, Serialize};
+
+    use super::{de, ser, HasFieldModulus};
+
+    #[derive(PartialEq, Debug, Clone, Serialize, Deserialize)]
+    struct Struct<F: LurkField> {
+        str: String,
+        int: i32,
+        ff: F,
+    }
+
+    #[derive(PartialEq, Debug, Clone, Serialize, Deserialize)]
+    enum Enum1<F: LurkField> {
+        CaseStr(String),
+        CaseInt(i32),
+        CaseFF(F),
+    }
+
+    impl<F: LurkField> HasFieldModulus for Struct<F> {
+        fn field_modulus() -> String {
+            F::MODULUS.to_string()
+        }
+    }
+
+    impl<F: LurkField> HasFieldModulus for Enum1<F> {
+        fn field_modulus() -> String {
+            F::MODULUS.to_string()
+        }
+    }
+
+    #[test]
+    fn struct_roundtrips() {
+        let s = Struct {
+            str: "hi".into(),
+            int: 42,
+            ff: Fq::double(&Fq::ONE),
+        };
+        assert_eq!(s, de(&ser(s.clone()).unwrap()).unwrap())
+    }
+
+    #[test]
+    fn enum1_roundtrips() {
+        let e11 = Enum1::CaseStr("bye".into());
+        let e12 = Enum1::CaseInt(11);
+        let e13 = Enum1::CaseFF(Fq::double(&Fq::double(&Fq::ONE)));
+        for e in [e11, e12, e13] {
+            assert_eq!(e, de(&ser(e.clone()).unwrap()).unwrap());
+        }
+    }
+
+    /// An enum can be deserialized to another, if the enum constructor has the
+    /// same index and uses the same inner data
+    #[test]
+    fn stable_enum() {
+        #[derive(PartialEq, Debug, Clone, Serialize, Deserialize)]
+        enum Enum2<F: LurkField> {
+            CaseStr2(String),
+            CaseInt2(i32),
+            CaseFF2(F),
+            Foo,
+        }
+
+        impl<F: LurkField> HasFieldModulus for Enum2<F> {
+            fn field_modulus() -> String {
+                F::MODULUS.to_string()
+            }
+        }
+        let e11 = Enum1::CaseStr("bye".into());
+        let e12 = Enum1::CaseInt(11);
+        let e13 = Enum1::CaseFF(Fq::double(&Fq::double(&Fq::ONE)));
+
+        let e21 = Enum2::CaseStr2("bye".into());
+        let e22 = Enum2::CaseInt2(11);
+        let e23 = Enum2::CaseFF2(Fq::double(&Fq::double(&Fq::ONE)));
+
+        for (e1, e2) in [(e11, e21), (e12, e22), (e13, e23)] {
+            assert_eq!(e2.clone(), de(&ser(e1.clone()).unwrap()).unwrap());
+            assert_eq!(e1, de(&ser(e2).unwrap()).unwrap());
+        }
+    }
+}