Implement HashOf statement and op (#217)

src/backends/plonky2/circuits/common.rs

@@ -7,7 +7,10 @@ use plonky2::{
         extension::Extendable,
         types::{Field, PrimeField64},
     },
-    hash::hash_types::{HashOutTarget, RichField, NUM_HASH_OUT_ELTS},
+    hash::{
+        hash_types::{HashOutTarget, RichField, NUM_HASH_OUT_ELTS},
+        poseidon::PoseidonHash,
+    },
     iop::{
         target::{BoolTarget, Target},
         witness::{PartialWitness, WitnessWrite},
@@ -320,6 +323,9 @@ pub trait CircuitBuilderPod<F: RichField + Extendable<D>, const D: usize> {
     /// and `y` each consist of two `u32` limbs.
     fn assert_i64_less_if(&mut self, b: BoolTarget, x: ValueTarget, y: ValueTarget);
 
+    /// Creates value target that is a hash of two given values.
+    fn hash_values(&mut self, x: ValueTarget, y: ValueTarget) -> ValueTarget;
+
     // Convenience methods for accessing and connecting elements of
     // (vectors of) flattenables.
     fn vec_ref<T: Flattenable>(&mut self, ts: &[T], i: Target) -> T;
@@ -455,6 +461,14 @@ impl CircuitBuilderPod<F, D> for CircuitBuilder<F, D> {
         assert_limb_lt(self, lhs, rhs);
     }
 
+    fn hash_values(&mut self, x: ValueTarget, y: ValueTarget) -> ValueTarget {
+        ValueTarget::from_slice(
+            &self
+                .hash_n_to_hash_no_pad::<PoseidonHash>([x.elements, y.elements].concat())
+                .elements,
+        )
+    }
+
     fn vec_ref<T: Flattenable>(&mut self, ts: &[T], i: Target) -> T {
         // TODO: Revisit this when we need more than 64 statements.
         let vector_ref = |builder: &mut CircuitBuilder<F, D>, v: &[Target], i| {

src/backends/plonky2/circuits/mainpod.rs

@@ -108,6 +108,7 @@ impl OperationVerifyGadget {
                     self.eval_copy(builder, st, op, &resolved_op_args)?,
                     self.eval_eq_from_entries(builder, st, op, &resolved_op_args),
                     self.eval_lt_lteq_from_entries(builder, st, op, &resolved_op_args),
+                    self.eval_hash_of(builder, st, op, &resolved_op_args),
                 ]
             },
             // Skip these if there are no resolved Merkle claims
@@ -275,6 +276,40 @@ impl OperationVerifyGadget {
         builder.all([op_st_code_ok, arg_types_ok, st_args_ok])
     }
 
+    fn eval_hash_of(
+        &self,
+        builder: &mut CircuitBuilder<F, D>,
+        st: &StatementTarget,
+        op: &OperationTarget,
+        resolved_op_args: &[StatementTarget],
+    ) -> BoolTarget {
+        let op_code_ok = op.has_native_type(builder, NativeOperation::HashOf);
+
+        let arg_types_ok = self.first_n_args_are_valueofs(builder, 3, resolved_op_args);
+
+        let arg1_value = resolved_op_args[0].args[1].as_value();
+        let arg2_value = resolved_op_args[1].args[1].as_value();
+        let arg3_value = resolved_op_args[2].args[1].as_value();
+
+        let expected_hash_value = builder.hash_values(arg2_value, arg3_value);
+
+        let hash_value_ok =
+            builder.is_equal_slice(&arg1_value.elements, &expected_hash_value.elements);
+
+        let arg1_key = resolved_op_args[0].args[0].clone();
+        let arg2_key = resolved_op_args[1].args[0].clone();
+        let arg3_key = resolved_op_args[2].args[0].clone();
+        let expected_statement = StatementTarget::new_native(
+            builder,
+            &self.params,
+            NativePredicate::HashOf,
+            &[arg1_key, arg2_key, arg3_key],
+        );
+        let st_ok = builder.is_equal_flattenable(st, &expected_statement);
+
+        builder.all([op_code_ok, arg_types_ok, hash_value_ok, st_ok])
+    }
+
     fn eval_none(
         &self,
         builder: &mut CircuitBuilder<F, D>,
@@ -533,7 +568,7 @@ mod tests {
             mainpod::{OperationArg, OperationAux},
             primitives::merkletree::{MerkleClaimAndProof, MerkleTree},
         },
-        middleware::{Hash, OperationType, PodId, RawValue},
+        middleware::{hash_values, Hash, OperationType, PodId, RawValue},
     };
 
     fn operation_verify(
@@ -939,6 +974,53 @@ mod tests {
         );
         operation_verify(st, op, prev_statements, merkle_proofs.clone())?;
 
+        // HashOf
+        let input_values = [
+            Value::from(RawValue([
+                GoldilocksField(1),
+                GoldilocksField(2),
+                GoldilocksField(3),
+                GoldilocksField(4),
+            ])),
+            Value::from(512),
+        ];
+        let v1 = hash_values(&input_values);
+        let [v2, v3] = input_values;
+
+        let st1: mainpod::Statement = Statement::ValueOf(
+            AnchoredKey::from((PodId(RawValue::from(88).into()), "hola")),
+            v1.into(),
+        )
+        .into();
+        let st2: mainpod::Statement = Statement::ValueOf(
+            AnchoredKey::from((PodId(RawValue::from(128).into()), "mundo")),
+            v2,
+        )
+        .into();
+        let st3: mainpod::Statement = Statement::ValueOf(
+            AnchoredKey::from((PodId(RawValue::from(256).into()), "!")),
+            v3,
+        )
+        .into();
+
+        let st: mainpod::Statement = Statement::HashOf(
+            AnchoredKey::from((PodId(RawValue::from(88).into()), "hola")),
+            AnchoredKey::from((PodId(RawValue::from(128).into()), "mundo")),
+            AnchoredKey::from((PodId(RawValue::from(256).into()), "!")),
+        )
+        .into();
+        let op = mainpod::Operation(
+            OperationType::Native(NativeOperation::HashOf),
+            vec![
+                OperationArg::Index(0),
+                OperationArg::Index(1),
+                OperationArg::Index(2),
+            ],
+            OperationAux::None,
+        );
+        let prev_statements = vec![st1, st2, st3];
+        operation_verify(st, op, prev_statements, merkle_proofs.clone())?;
+
         // NotContainsFromEntries
         let kvs = [
             (1.into(), 55.into()),

src/frontend/mod.rs

@@ -7,9 +7,10 @@ use itertools::Itertools;
 use serde::{Deserialize, Serialize};
 
 use crate::middleware::{
-    self, check_st_tmpl, hash_str, AnchoredKey, Key, MainPodInputs, NativeOperation,
-    NativePredicate, OperationAux, OperationType, Params, PodId, PodProver, PodSigner, Predicate,
-    Statement, StatementArg, Value, WildcardValue, EMPTY_VALUE, KEY_TYPE, SELF,
+    self, check_st_tmpl, hash_str, hash_values, AnchoredKey, Hash, Key, MainPodInputs,
+    NativeOperation, NativePredicate, OperationAux, OperationType, Params, PodId, PodProver,
+    PodSigner, Predicate, Statement, StatementArg, Value, WildcardValue, EMPTY_VALUE, KEY_TYPE,
+    SELF,
 };
 
 mod custom;
@@ -435,6 +436,26 @@ impl MainPodBuilder {
                         return Err(Error::op_invalid_args("max-of".to_string()));
                     }
                 },
+                HashOf => match (args[0].clone(), args[1].clone(), args[2].clone()) {
+                    (
+                        OperationArg::Statement(Statement::ValueOf(ak0, v0)),
+                        OperationArg::Statement(Statement::ValueOf(ak1, v1)),
+                        OperationArg::Statement(Statement::ValueOf(ak2, v2)),
+                    ) => {
+                        if Hash::from(v0.raw()) == hash_values(&[v1, v2]) {
+                            vec![
+                                StatementArg::Key(ak0),
+                                StatementArg::Key(ak1),
+                                StatementArg::Key(ak2),
+                            ]
+                        } else {
+                            return Err(Error::op_invalid_args("hash-of".to_string()));
+                        }
+                    }
+                    _ => {
+                        return Err(Error::op_invalid_args("hash-of".to_string()));
+                    }
+                },
                 ContainsFromEntries => self.op_args_entries(public, args)?,
                 NotContainsFromEntries => self.op_args_entries(public, args)?,
                 _ => Err(Error::custom(format!(

src/middleware/basetypes.rs

@@ -58,7 +58,7 @@ use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 
 use super::serialization::*;
-use crate::middleware::{Params, ToFields};
+use crate::middleware::{Params, ToFields, Value};
 
 /// F is the native field we use everywhere.  Currently it's Goldilocks from plonky2
 pub type F = GoldilocksField;
@@ -164,6 +164,10 @@ pub fn hash_fields(input: &[F]) -> Hash {
     Hash(PoseidonHash::hash_no_pad(input).elements)
 }
 
+pub fn hash_values(input: &[Value]) -> Hash {
+    hash_fields(&input.iter().flat_map(|v| v.raw().0).collect::<Vec<_>>())
+}
+
 impl From<RawValue> for Hash {
     fn from(v: RawValue) -> Self {
         Hash(v.0)

src/middleware/operation.rs

@@ -69,6 +69,7 @@ pub enum NativeOperation {
     SumOf = 11,
     ProductOf = 12,
     MaxOf = 13,
+    HashOf = 14,
 
     // Syntactic sugar operations.  These operations are not supported by the backend.  The
     // frontend compiler is responsible of translating these operations into the operations above.
@@ -119,6 +120,7 @@ impl OperationType {
                 NativeOperation::SumOf => Some(Predicate::Native(NativePredicate::SumOf)),
                 NativeOperation::ProductOf => Some(Predicate::Native(NativePredicate::ProductOf)),
                 NativeOperation::MaxOf => Some(Predicate::Native(NativePredicate::MaxOf)),
+                NativeOperation::HashOf => Some(Predicate::Native(NativePredicate::HashOf)),
                 no => unreachable!("Unexpected syntactic sugar op {:?}", no),
             },
             OperationType::Custom(cpr) => Some(Predicate::Custom(cpr.clone())),
@@ -152,6 +154,7 @@ pub enum Operation {
     SumOf(Statement, Statement, Statement),
     ProductOf(Statement, Statement, Statement),
     MaxOf(Statement, Statement, Statement),
+    HashOf(Statement, Statement, Statement),
     Custom(CustomPredicateRef, Vec<Statement>),
 }
 
@@ -174,6 +177,7 @@ impl Operation {
             Self::SumOf(_, _, _) => OT::Native(SumOf),
             Self::ProductOf(_, _, _) => OT::Native(ProductOf),
             Self::MaxOf(_, _, _) => OT::Native(MaxOf),
+            Self::HashOf(_, _, _) => OT::Native(HashOf),
             Self::Custom(cpr, _) => OT::Custom(cpr.clone()),
         }
     }
@@ -194,6 +198,7 @@ impl Operation {
             Self::SumOf(s1, s2, s3) => vec![s1, s2, s3],
             Self::ProductOf(s1, s2, s3) => vec![s1, s2, s3],
             Self::MaxOf(s1, s2, s3) => vec![s1, s2, s3],
+            Self::HashOf(s1, s2, s3) => vec![s1, s2, s3],
             Self::Custom(_, args) => args,
         }
     }
@@ -250,6 +255,9 @@ impl Operation {
                     Self::ProductOf(s1, s2, s3)
                 }
                 (NO::MaxOf, (Some(s1), Some(s2), Some(s3)), OA::None, 3) => Self::MaxOf(s1, s2, s3),
+                (NO::HashOf, (Some(s1), Some(s2), Some(s3)), OA::None, 3) => {
+                    Self::HashOf(s1, s2, s3)
+                }
                 _ => Err(Error::custom(format!(
                     "Ill-formed operation {:?} with arguments {:?}.",
                     op_code, args

src/middleware/statement.rs

@@ -32,6 +32,7 @@ pub enum NativePredicate {
     SumOf = 8,
     ProductOf = 9,
     MaxOf = 10,
+    HashOf = 11,
 
     // Syntactic sugar predicates.  These predicates are not supported by the backend.  The
     // frontend compiler is responsible of translating these predicates into the predicates above.
@@ -102,6 +103,7 @@ pub enum Statement {
     SumOf(AnchoredKey, AnchoredKey, AnchoredKey),
     ProductOf(AnchoredKey, AnchoredKey, AnchoredKey),
     MaxOf(AnchoredKey, AnchoredKey, AnchoredKey),
+    HashOf(AnchoredKey, AnchoredKey, AnchoredKey),
     Custom(CustomPredicateRef, Vec<WildcardValue>),
 }
 
@@ -123,6 +125,7 @@ impl Statement {
             Self::SumOf(_, _, _) => Native(NativePredicate::SumOf),
             Self::ProductOf(_, _, _) => Native(NativePredicate::ProductOf),
             Self::MaxOf(_, _, _) => Native(NativePredicate::MaxOf),
+            Self::HashOf(_, _, _) => Native(NativePredicate::HashOf),
             Self::Custom(cpr, _) => Custom(cpr.clone()),
         }
     }
@@ -140,6 +143,7 @@ impl Statement {
             Self::SumOf(ak1, ak2, ak3) => vec![Key(ak1), Key(ak2), Key(ak3)],
             Self::ProductOf(ak1, ak2, ak3) => vec![Key(ak1), Key(ak2), Key(ak3)],
             Self::MaxOf(ak1, ak2, ak3) => vec![Key(ak1), Key(ak2), Key(ak3)],
+            Self::HashOf(ak1, ak2, ak3) => vec![Key(ak1), Key(ak2), Key(ak3)],
             Self::Custom(_, args) => Vec::from_iter(args.into_iter().map(WildcardLiteral)),
         }
     }