A helper trait for file methods of CommitmentKey

examples/kzg_keygen_tools.rs

@@ -10,7 +10,7 @@ use nova_snark::{
     hyperkzg::{CommitmentEngine, CommitmentKey},
     Bn256EngineKZG,
   },
-  traits::commitment::CommitmentEngineTrait,
+  traits::commitment::{CommitmentEngineTrait, CommitmentKeyFileTrait},
 };
 use rand_core::OsRng;
 

src/provider/hyperkzg.rs

@@ -10,13 +10,14 @@ use crate::{
   errors::NovaError,
   gadgets::utils::to_bignat_repr,
   provider::{
+    check_sanity_of_ptau_file,
     ptau::PtauFileError,
     read_ptau,
     traits::{DlogGroup, DlogGroupExt, PairingGroup},
     write_ptau,
   },
   traits::{
-    commitment::{CommitmentEngineTrait, CommitmentTrait, Len},
+    commitment::{CommitmentEngineTrait, CommitmentKeyFileTrait, CommitmentTrait, Len},
     evaluation::EvaluationEngineTrait,
     AbsorbInRO2Trait, AbsorbInROTrait, Engine, ROTrait, TranscriptEngineTrait, TranscriptReprTrait,
   },
@@ -135,12 +136,12 @@ where
   }
 }
 
-impl<E: Engine> CommitmentKey<E>
+impl<E: Engine> CommitmentKeyFileTrait for CommitmentKey<E>
 where
   E::GE: PairingGroup,
 {
   /// Save keys
-  pub fn save_to(
+  fn save_to(
     &self,
     mut writer: &mut (impl std::io::Write + std::io::Seek),
   ) -> Result<(), PtauFileError> {
@@ -151,6 +152,14 @@ where
 
     write_ptau(&mut writer, g1_points, g2_points, power)
   }
+
+  fn check_sanity_of_key_file(
+    path: impl AsRef<std::path::Path>,
+    num_g1: usize,
+    num_g2: usize,
+  ) -> Result<(), PtauFileError> {
+    check_sanity_of_ptau_file::<<E::GE as DlogGroup>::AffineGroupElement>(&path, num_g1, num_g2)
+  }
 }
 
 impl<E: Engine> Default for Commitment<E>

src/provider/pedersen.rs

@@ -7,7 +7,7 @@ use crate::{
     traits::{DlogGroup, DlogGroupExt},
   },
   traits::{
-    commitment::{CommitmentEngineTrait, CommitmentTrait, Len},
+    commitment::{CommitmentEngineTrait, CommitmentKeyFileTrait, CommitmentTrait, Len},
     AbsorbInRO2Trait, AbsorbInROTrait, Engine, ROTrait, TranscriptReprTrait,
   },
 };
@@ -21,6 +21,7 @@ use num_integer::Integer;
 use num_traits::ToPrimitive;
 use rayon::prelude::*;
 use serde::{Deserialize, Serialize};
+use std::{fs::File, io::Read};
 
 const KEY_FILE_HEAD: [u8; 12] = *b"PEDERSEN_KEY";
 
@@ -188,17 +189,32 @@ pub struct CommitmentEngine<E: Engine> {
   _p: PhantomData<E>,
 }
 
-impl<E: Engine> CommitmentKey<E>
+impl<E: Engine> CommitmentKeyFileTrait for CommitmentKey<E>
 where
   E::GE: DlogGroup,
 {
-  pub fn save_to(&self, writer: &mut impl std::io::Write) -> Result<(), PtauFileError> {
+  fn save_to(&self, writer: &mut impl std::io::Write) -> Result<(), PtauFileError> {
     writer.write_all(&KEY_FILE_HEAD)?;
     let mut points = Vec::with_capacity(self.ck.len() + 1);
     points.push(self.h);
     points.extend(self.ck.iter().cloned());
     write_points(writer, points)
   }
+
+  fn check_sanity_of_key_file(
+    path: impl AsRef<std::path::Path>,
+    _num_g1: usize,
+    _num_g2: usize,
+  ) -> Result<(), PtauFileError> {
+    let mut reader = File::open(path)?;
+    let mut head = [0u8; 12];
+    reader.read_exact(&mut head)?;
+    if head != KEY_FILE_HEAD {
+      Err(PtauFileError::InvalidHead)
+    } else {
+      Ok(())
+    }
+  }
 }
 
 impl<E: Engine> CommitmentEngineTrait<E> for CommitmentEngine<E>

src/traits/commitment.rs

@@ -12,6 +12,7 @@ use num_integer::Integer;
 use num_traits::ToPrimitive;
 use rayon::iter::{IndexedParallelIterator, IntoParallelRefIterator, ParallelIterator};
 use serde::{Deserialize, Serialize};
+use std::path::Path;
 
 /// A helper trait for types implementing scalar multiplication.
 pub trait ScalarMul<Rhs, Output = Self>: Mul<Rhs, Output = Output> + MulAssign<Rhs> {}
@@ -48,11 +49,34 @@ pub trait Len {
   fn length(&self) -> usize;
 }
 
+/// A trait for saving key to a writer and checking sanity of key file
+pub trait CommitmentKeyFileTrait {
+  /// Saves the key to the provided writer.
+  fn save_to(
+    &self,
+    writer: &mut (impl std::io::Write + std::io::Seek),
+  ) -> Result<(), PtauFileError>;
+
+  /// Checks the sanity of the key file at the provided path.
+  fn check_sanity_of_key_file(
+    path: impl AsRef<Path>,
+    num_g1: usize,
+    num_g2: usize,
+  ) -> Result<(), PtauFileError>;
+}
+
 /// A trait that ties different pieces of the commitment generation together
 pub trait CommitmentEngineTrait<E: Engine>: Clone + Send + Sync {
   /// Holds the type of the commitment key
   /// The key should quantify its length in terms of group generators.
-  type CommitmentKey: Len + Clone + Debug + Send + Sync + Serialize + for<'de> Deserialize<'de>;
+  type CommitmentKey: Len
+    + CommitmentKeyFileTrait
+    + Clone
+    + Debug
+    + Send
+    + Sync
+    + Serialize
+    + for<'de> Deserialize<'de>;
 
   /// Holds the type of the derandomization key
   type DerandKey: Clone + Debug + Send + Sync + Serialize + for<'de> Deserialize<'de>;