Document PSE fork features (privacy-scaling-explorations#226)

* fix: panic if input or table contains simple selector in `lookup_any` * fix: include `shuffle` in `Debug` of `PinnedConstraintSystem` if it is not empty * doc: add `book/src/user/experimental-features.md` * doc: apply suggestion from Carlos and add more links to doc page and example * doc: mention `experimental-features.md` in `README.md`
taikoxyz · Nov 10, 2023 · 324c886 · 324c886
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diff --git a/README.md b/README.md
@@ -1,6 +1,8 @@
 # halo2 [![Crates.io](https://img.shields.io/crates/v/halo2.svg)](https://crates.io/crates/halo2) #
 
-## [Documentation](https://docs.rs/halo2)
+## [Documentation](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs)
+
+For experimental features `privacy-scaling-explorations/halo2` fork adds, please refer to [`experimental-features.md`](./book/src/user/experimental-features.md).
 
 ## Minimum Supported Rust Version
 

diff --git a/book/src/SUMMARY.md b/book/src/SUMMARY.md
@@ -12,6 +12,7 @@
   - [Lookup tables](user/lookup-tables.md)
   - [Gadgets](user/gadgets.md)
   - [Tips and tricks](user/tips-and-tricks.md)
+  - [Experimental features](user/experimental-features.md)
 - [Design](design.md)
   - [Proving system](design/proving-system.md)
     - [Lookup argument](design/proving-system/lookup.md)

diff --git a/book/src/user/experimental-features.md b/book/src/user/experimental-features.md
@@ -0,0 +1,140 @@
+# Experimental features
+
+In `privacy-scaling-explorations/halo2` fork we have implemented many experimental features to cover different use cases, especially for those with huge circuits. We collect them in this page for easier tracking and referencing.
+
+## Commitment scheme abstraction
+
+To support different kinds of polynomial commitment schemes, we've added a trait `CommitmentScheme` to allow create/verify proofs with different commitment scheme implementations, currently there are 2 available implementations in this fork:
+
+- [`IPACommitmentScheme`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/poly/ipa/commitment/struct.IPACommitmentScheme.html)
+
+  The original implementation from `zcash/halo2` with the original multi-open strategy `{Prover,Verifier}IPA`
+
+- [`KZGCommitmentScheme`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/poly/kzg/commitment/struct.KZGCommitmentScheme.html)
+
+  KZG commitment scheme as in [GWC19](https://eprint.iacr.org/2019/953), which doesn't commit the instance columns, with 2 multi-open strategies available:
+
+  - `{Prover,Verifier}GWC` - The original strategy in [GWC19](https://eprint.iacr.org/2019/953)
+  - `{Prover,Verifier}SHPLONK` - The strategy proposed in [BDFG20](https://eprint.iacr.org/2020/081)
+
+When using `create_proof` and `verify_proof`, we need to specify the commitment scheme and multi-open strategy like:
+
+```rust
+// Using IPA
+create_proof<IPACommitmentScheme<_>, ProverIPA<_>, _, _, _, _>
+verify_proof<IPACommitmentScheme<_>, ProverIPA<_>, _, _, _>
+
+// Using KZG with GWC19 mutli-open strategy
+create_proof<KZGCommitmentScheme<_>, ProverGWC<_>, _, _, _, _>
+verify_proof<KZGCommitmentScheme<_>, ProverGWC<_>, _, _, _>
+
+// Using KZG with BDFG20 mutli-open strategy
+create_proof<KZGCommitmentScheme<_>, ProverSHPLONK<_>, _, _, _, _>
+verify_proof<KZGCommitmentScheme<_>, ProverSHPLONK<_>, _, _, _>
+```
+
+## `ConstraintSystem` extension
+
+### Dynamic lookup
+
+[`ConstraintSystem::lookup_any`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/plonk/struct.ConstraintSystem.html#method.lookup_any) is added for use cases that need to lookup dynamic table instead of fixed table.
+
+Unlike `ConstraintSystem::lookup` which only allows `TableColumn`(s) as table, it allows any `Expression`(s) without simple selector.
+
+### Shuffle
+
+[`ConstraintSystem::shuffle`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/plonk/struct.ConstraintSystem.html#method.shuffle) is added for use cases that only need shuffle without pre-defined mapping.
+
+It allows us to prove any `Expression`(s) without simple selector is shuffled from the other. For example `halo2_proofs/examples/shuffle_api.rs` shows how to prove two lists of 2-tuples are shuffled of each other.
+
+### Multi-phase
+
+[`ConstraintSystem::advice_column_in`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/plonk/struct.ConstraintSystem.html#method.advice_column_in) and [`ConstraintSystem::challenge_usable_after`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/plonk/struct.ConstraintSystem.html#method.challenge_usable_after) are added for use cases that build PIOP sub-routine themselves, currently it supports up-to 3 phases as `{First,Second,Third}Phase`.
+
+It allows us to allocate advice column in different interactive phases with extra challenges squeezed in-between. For example in `halo2_proofs/examples/shuffle.rs` it shows how to build a customized shuffle argument with such API.
+
+### Unblinded advice column
+
+[`ConstraintSystem::unblinded_advice_column`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/plonk/struct.ConstraintSystem.html#method.unblinded_advice_column) is added for use cases that want to re-use advice column commitment among different proofs. For example in `halo2_proofs/examples/vector-ops-unblinded.rs` it shows with this API and same assignment, two advice commitment frmo different proof can be same.
+
+Worth mentioning, re-using advice column commitment in different proofs will need more blinding factors than the amount that prover adds, otherwise some information will be leaked and it's no longer perfect zero-knowledge.
+
+## [`Expression`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/plonk/enum.Expression.html) extension
+
+- [`Expression::Challenge`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/plonk/enum.Expression.html#variant.Challenge)
+
+  A variant added for multi-phase. It can be obtained by [`ConstraintSystem::challenge_usable_after`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/plonk/struct.ConstraintSystem.html#method.challenge_usable_after) and used as a pseudo-random constant.
+
+- [`Expression::identifier`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/plonk/enum.Expression.html#method.identifier)
+
+  It prints `Expression` in a less verbose and human-readable way.
+
+## [`Circuit`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/plonk/trait.Circuit.html) extension
+
+- [`Circuit::Params`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/plonk/trait.Circuit.html#associatedtype.Params)
+
+  To use this, feature `circuit-params` needs to be turned on.
+
+  A associated type added for configuring circuit with runtime parameter. 
+
+  It allows us to implement [`Circuit::params`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/plonk/trait.Circuit.html#method.params) to return the parameter of a circuit, and implement [`Circuit::configure_with_params`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/plonk/trait.Circuit.html#method.configure_with_params) to configure circuit with runtime parameter retrieved earlier.
+
+## [`ProvingKey`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/plonk/struct.ProvingKey.html) & [`VerifyingKey`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/plonk/struct.VerifyingKey.html) de/serialization and [`SerdeFormat`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/enum.SerdeFormat.html)
+
+`ProvingKey::{read,write}` and `VerifyingKey::{read,write}` is added to serialize proving key and verifying key.
+
+For field elements and elliptic curve points inside pk and vk, currently we have 3 different de/serialization format:
+
+- [`SerdeFormat::Processed`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/enum.SerdeFormat.html#variant.Processed)
+
+  It de/serializes them as `PrimeField::Repr` and `GroupEncoding::Repr` respectively, and checks all elements are valid.
+
+- [`SerdeFormat::RawBytes`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/enum.SerdeFormat.html#variant.RawBytes)
+
+  It de/serializes them as `SerdeObject::{from_raw_bytes,to_raw_bytes}` respectively, and checks all elements are valid.
+
+- [`SerdeFormat::RawBytesUnchecked`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/enum.SerdeFormat.html#variant.RawBytesUnchecked)
+
+  It de/serializes them as `SerdeObject::{from_raw_bytes,to_raw_bytes}` respectively, without checking if elements are valid.
+
+Also `ParamsKZG::{read_custom,write_custom}` follows the same rule, and by default `ParamsKZG::{read,write}` uses `SerdeFormat::RawBytes` for efficiency.
+
+## Thread safe [`Region`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/circuit/struct.Region.html)
+
+To use this, feature `thread-safe-region` needs to be turned on.
+
+It constrains the `RegionLayouter` to be `Send` so we can have a `Region` in different threads. It's useful when we want to arrange witness computation and assignment in the same place, but still keep the function `Send` so the caller can parallelize multiple of them.
+
+For example `halo2_proofs/examples/vector-mul.rs` shows how to parallelize region computation and assignment.
+
+## Optional selector compression
+
+Currently [`keygen_vk`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/plonk/fn.keygen_vk.html) changes configured `ConstraintSystem` to compresses simple selectors into smaller set of fixed columns to reduce cost.
+
+For some use cases that want to keep configured `ConstraintSystem` unchanged they can do the verifying key generation by calling [`keygen_vk_custom`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/plonk/fn.keygen_vk_custom.html) with second argument as `false` instead, which disables the selector compression.
+
+## [`MockProver`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/dev/struct.MockProver.html) improvement
+
+- [`MockProver::verify_par`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/dev/struct.MockProver.html#method.verify_par)
+
+  Same checks as `MockProver::verify`, but parallelized.
+
+- [`MockProver::verify_at_rows`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/dev/struct.MockProver.html#method.verify_at_rows)
+
+  Same checks as `MockProver::verify`, but only on specified rows.
+
+- [`MockProver::verify_at_rows_par`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/dev/struct.MockProver.html#method.verify_at_rows_par)
+
+  Same checks as `MockProver::verify_at_rows`, but parallelized.
+
+- [`MockProver::assert_satisfied_par`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/dev/struct.MockProver.html#method.assert_satisfied_par)
+
+  Same assertions as `MockProver::assert_satisfied`, but parallelized.
+
+- [`MockProver::assert_satisfied_at_rows_par`](https://privacy-scaling-explorations.github.io/halo2/halo2_proofs/dev/struct.MockProver.html#method.assert_satisfied_at_rows_par)
+
+  Same assertions as `MockProver::assert_satisfied_par`, but only on specified rows.
+
+## `Evaluator` and `evaluate_h`
+
+They are introduced to improve quotient computation speed and memory usage for circuit with complicated `Expression`.
diff --git a/halo2_proofs/src/plonk/circuit.rs b/halo2_proofs/src/plonk/circuit.rs
@@ -1640,7 +1640,11 @@ impl<'a, F: Field> std::fmt::Debug for PinnedConstraintSystem<'a, F> {
             .field("instance_queries", self.instance_queries)
             .field("fixed_queries", self.fixed_queries)
             .field("permutation", self.permutation)
-            .field("lookups", self.lookups)
+            .field("lookups", self.lookups);
+        if !self.shuffles.is_empty() {
+            debug_struct.field("shuffles", self.shuffles);
+        }
+        debug_struct
             .field("constants", self.constants)
             .field("minimum_degree", self.minimum_degree);
         debug_struct.finish()
@@ -1771,6 +1775,12 @@ impl<F: Field> ConstraintSystem<F> {
         let table_map = table_map(&mut cells)
             .into_iter()
             .map(|(mut input, mut table)| {
+                if input.contains_simple_selector() {
+                    panic!("expression containing simple selector supplied to lookup argument");
+                }
+                if table.contains_simple_selector() {
+                    panic!("expression containing simple selector supplied to lookup argument");
+                }
                 input.query_cells(&mut cells);
                 table.query_cells(&mut cells);
                 (input, table)
@@ -2212,6 +2222,10 @@ impl<F: Field> ConstraintSystem<F> {
     }
 
     /// Allocate a new advice column in given phase
+    ///
+    /// # Panics
+    ///
+    /// It panics if previous phase before the given one doesn't have advice column allocated.
     pub fn advice_column_in<P: Phase>(&mut self, phase: P) -> Column<Advice> {
         let phase = phase.to_sealed();
         if let Some(previous_phase) = phase.prev() {
@@ -2242,6 +2256,10 @@ impl<F: Field> ConstraintSystem<F> {
     }
 
     /// Requests a challenge that is usable after the given phase.
+    ///
+    /// # Panics
+    ///
+    /// It panics if the given phase doesn't have advice column allocated.
     pub fn challenge_usable_after<P: Phase>(&mut self, phase: P) -> Challenge {
         let phase = phase.to_sealed();
         self.assert_phase_exists(