diff --git a/halo2_proofs/src/dev.rs b/halo2_proofs/src/dev.rs
index 1d9de2706e..28ca17a082 100644
--- a/halo2_proofs/src/dev.rs
+++ b/halo2_proofs/src/dev.rs
@@ -1443,7 +1443,7 @@ impl<'a, F: FieldExt> MockProver<'a, F> {
             self.permutation
                 .as_ref()
                 .expect("root cs permutation must be Some")
-                .mapping
+                .mapping()
                 .iter()
                 .enumerate()
                 .flat_map(move |(column, values)| {
@@ -1817,7 +1817,7 @@ impl<'a, F: FieldExt> MockProver<'a, F> {
             self.permutation
                 .as_ref()
                 .expect("root cs permutation must be Some")
-                .mapping
+                .mapping()
                 .iter()
                 .enumerate()
                 .flat_map(move |(column, values)| {
diff --git a/halo2_proofs/src/plonk.rs b/halo2_proofs/src/plonk.rs
index d1aecca38e..f2e2ce7df8 100644
--- a/halo2_proofs/src/plonk.rs
+++ b/halo2_proofs/src/plonk.rs
@@ -28,7 +28,7 @@ mod error;
 mod evaluation;
 mod keygen;
 mod lookup;
-pub(crate) mod permutation;
+pub mod permutation;
 mod vanishing;
 
 mod prover;
diff --git a/halo2_proofs/src/plonk/permutation.rs b/halo2_proofs/src/plonk/permutation.rs
index b353493c57..8a731416ee 100644
--- a/halo2_proofs/src/plonk/permutation.rs
+++ b/halo2_proofs/src/plonk/permutation.rs
@@ -1,3 +1,5 @@
+//! Implementation of permutation argument.
+
 use super::circuit::{Any, Column};
 use crate::{
     arithmetic::CurveAffine,
@@ -14,6 +16,8 @@ pub(crate) mod keygen;
 pub(crate) mod prover;
 pub(crate) mod verifier;
 
+pub use keygen::Assembly;
+
 use std::io;
 
 /// A permutation argument.
@@ -72,6 +76,7 @@ impl Argument {
         }
     }
 
+    /// Returns columns that participate on the permutation argument.
     pub fn get_columns(&self) -> Vec<Column<Any>> {
         self.columns.clone()
     }
diff --git a/halo2_proofs/src/plonk/permutation/keygen.rs b/halo2_proofs/src/plonk/permutation/keygen.rs
index 58ba4878cc..cc2dc09bb0 100644
--- a/halo2_proofs/src/plonk/permutation/keygen.rs
+++ b/halo2_proofs/src/plonk/permutation/keygen.rs
@@ -12,16 +12,16 @@ use crate::{
 };
 
 /// Struct that accumulates all the necessary data in order to construct the permutation argument.
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq)]
 pub struct Assembly {
     /// Columns that participate on the copy permutation argument.
-    pub columns: Vec<Column<Any>>,
+    columns: Vec<Column<Any>>,
     /// Mapping of the actual copies done.
-    pub mapping: Vec<Vec<(usize, usize)>>,
+    mapping: Vec<Vec<(usize, usize)>>,
     /// Some aux data used to swap positions directly when sorting.
-    pub aux: Vec<Vec<(usize, usize)>>,
+    aux: Vec<Vec<(usize, usize)>>,
     /// More aux data
-    pub sizes: Vec<Vec<usize>>,
+    sizes: Vec<Vec<usize>>,
 }
 
 impl Assembly {
@@ -238,4 +238,14 @@ impl Assembly {
             polys,
         }
     }
+
+    /// Returns columns that participate on the permutation argument.
+    pub fn columns(&self) -> &[Column<Any>] {
+        &self.columns
+    }
+
+    /// Returns mappings of the copies.
+    pub fn mapping(&self) -> &[Vec<(usize, usize)>] {
+        &self.mapping
+    }
 }
diff --git a/rust-toolchain b/rust-toolchain
index af92bdd9f5..9405730420 100644
--- a/rust-toolchain
+++ b/rust-toolchain
@@ -1 +1 @@
-1.63.0
+1.64.0