recursive_verifier: Introduce Verifier gadget

halo2/src/accumulator.rs

@@ -0,0 +1,68 @@
+pub mod prover;
+pub mod verifier;
+
+use std::marker::PhantomData;
+
+use halo2_proofs::{arithmetic::CurveAffine, circuit::Value};
+pub use verifier::Verifier;
+
+type InstanceColumn = Vec<Value<bool>>;
+type Instance = Vec<InstanceColumn>;
+
+trait Accumulator<C: CurveAffine> {
+    /// An evaluation claim (C, z) corresponding to an old instance
+    type Input;
+    /// An evaluation claim (C', z') corresponding to the new accumulator
+    type Output: Into<Instance> + Copy;
+    // /// Witness value
+    // /// (e.g. in IPA, we can put challenges into witness)
+    // type Witness;
+
+    /// Read a previous instance (C, z), encoded as a public input to
+    /// the proof being checked
+    fn read_instance(instances: &[Instance]) -> Self::Input;
+
+    /// Read the new accumulator (C', z'), encoded as a public input to the
+    /// proof being checked, where C' := ∑ [ß^i] G_i is a random linear
+    /// combination of the commitments to IPA challenges G_i's in the old instances.
+    /// The new C' is evaluated at a random challenge z'.
+    fn read_new_acc(instances: &[Instance]) -> Self::Output;
+
+    /// Check that the new accumulator (C', z') was correctly constructed from
+    /// the old instances.
+    fn check_new_acc(
+        accs: &[Self::Input],
+        new_acc: Self::Output,
+        is_base_case: Value<bool>,
+    ) -> Value<bool>;
+}
+
+#[derive(Clone, Copy)]
+struct SplitAccumulator<C: CurveAffine>(PhantomData<C>);
+
+impl<C: CurveAffine> Into<Instance> for SplitAccumulator<C> {
+    fn into(self) -> Instance {
+        vec![]
+    }
+}
+
+impl<C: CurveAffine> Accumulator<C> for SplitAccumulator<C> {
+    type Input = Self;
+    type Output = Self;
+
+    fn read_instance(_instances: &[Instance]) -> Self::Input {
+        Self(PhantomData)
+    }
+
+    fn read_new_acc(_instances: &[Instance]) -> Self::Input {
+        Self(PhantomData)
+    }
+
+    fn check_new_acc(
+        _accs: &[Self::Input],
+        _new_acc: Self::Output,
+        is_base_case: Value<bool>,
+    ) -> Value<bool> {
+        Value::known(true)
+    }
+}

halo2/src/accumulator/prover.rs

@@ -0,0 +1 @@
+