From 7439d2424b1ab425ea74f257f77c92f42a1f6801 Mon Sep 17 00:00:00 2001
From: Sam Kim <skim13@cs.stanford.edu>
Date: Tue, 4 Jan 2022 07:31:24 -0500
Subject: [PATCH] feat: add a separate TranscriptError

---
 zk-token-sdk/src/errors.rs             |  6 ++++++
 zk-token-sdk/src/range_proof/errors.rs | 11 ++++++++++-
 zk-token-sdk/src/range_proof/mod.rs    | 11 +++--------
 zk-token-sdk/src/transcript.rs         |  8 ++++----
 4 files changed, 23 insertions(+), 13 deletions(-)

diff --git a/zk-token-sdk/src/errors.rs b/zk-token-sdk/src/errors.rs
index cd846199c..d494fde0c 100644
--- a/zk-token-sdk/src/errors.rs
+++ b/zk-token-sdk/src/errors.rs
@@ -10,3 +10,9 @@ pub enum ProofError {
     )]
     InconsistentCTData,
 }
+
+#[derive(Error, Clone, Debug, Eq, PartialEq)]
+pub enum TranscriptError {
+    #[error("point is the identity")]
+    ValidationError,
+}
diff --git a/zk-token-sdk/src/range_proof/errors.rs b/zk-token-sdk/src/range_proof/errors.rs
index fd33bb58f..f9f7b3410 100644
--- a/zk-token-sdk/src/range_proof/errors.rs
+++ b/zk-token-sdk/src/range_proof/errors.rs
@@ -1,8 +1,9 @@
 //! Errors related to proving and verifying proofs.
 use thiserror::Error;
+use crate::errors::TranscriptError;
 
 #[derive(Error, Clone, Debug, Eq, PartialEq)]
-pub enum ProofError {
+pub enum RangeProofError {
     #[error("the required algebraic relation does not hold")]
     AlgebraicRelationError,
     #[error("malformed proof")]
@@ -11,6 +12,14 @@ pub enum ProofError {
     InvalidBitsize,
     #[error("insufficient generators for the proof")]
     InvalidGeneratorsLength,
+    #[error("transcript failed to produce a challenge")]
+    TranscriptError,
     #[error("number of blinding factors do not match the number of values")]
     WrongNumBlindingFactors,
 }
+
+impl From<TranscriptError> for RangeProofError {
+    fn from(err: TranscriptError) -> Self {
+        Self::TranscriptError
+    }
+}
diff --git a/zk-token-sdk/src/range_proof/mod.rs b/zk-token-sdk/src/range_proof/mod.rs
index f827bf9dd..37fbd89f8 100644
--- a/zk-token-sdk/src/range_proof/mod.rs
+++ b/zk-token-sdk/src/range_proof/mod.rs
@@ -8,8 +8,7 @@ use {
 use {
     crate::{
         encryption::pedersen::PedersenBase,
-        errors::ProofError,
-        range_proof::{generators::BulletproofGens, inner_product::InnerProductProof},
+        range_proof::{errors::RangeProofError, generators::BulletproofGens, inner_product::InnerProductProof},
         transcript::TranscriptProtocol,
     },
     core::iter,
@@ -222,7 +221,7 @@ impl RangeProof {
         comms: Vec<&CompressedRistretto>,
         bit_lengths: Vec<usize>,
         transcript: &mut Transcript,
-    ) -> Result<(), ProofError> {
+    ) -> Result<(), RangeProofError> {
         let G = PedersenBase::default().G;
         let H = PedersenBase::default().H;
 
@@ -231,11 +230,7 @@ impl RangeProof {
         let bp_gens = BulletproofGens::new(nm);
 
         if !nm.is_power_of_two() {
-            return Err(ProofError::InvalidBitsize);
-        }
-
-        if !(nm == 8 || nm == 16 || nm == 32 || nm == 64 || nm == 128) {
-            return Err(ProofError::InvalidBitsize);
+            return Err(RangeProofError::InvalidBitsize);
         }
 
         transcript.validate_and_append_point(b"A", &self.A)?;
diff --git a/zk-token-sdk/src/transcript.rs b/zk-token-sdk/src/transcript.rs
index 836ef2635..d989e2c44 100644
--- a/zk-token-sdk/src/transcript.rs
+++ b/zk-token-sdk/src/transcript.rs
@@ -1,5 +1,5 @@
 use {
-    crate::errors::ProofError,
+    crate::errors::TranscriptError,
     curve25519_dalek::{ristretto::CompressedRistretto, scalar::Scalar, traits::IsIdentity},
     merlin::Transcript,
 };
@@ -40,7 +40,7 @@ pub trait TranscriptProtocol {
         &mut self,
         label: &'static [u8],
         point: &CompressedRistretto,
-    ) -> Result<(), ProofError>;
+    ) -> Result<(), TranscriptError>;
 
     /// Compute a `label`ed challenge variable.
     fn challenge_scalar(&mut self, label: &'static [u8]) -> Scalar;
@@ -90,9 +90,9 @@ impl TranscriptProtocol for Transcript {
         &mut self,
         label: &'static [u8],
         point: &CompressedRistretto,
-    ) -> Result<(), ProofError> {
+    ) -> Result<(), TranscriptError> {
         if point.is_identity() {
-            Err(ProofError::VerificationError)
+            Err(TranscriptError::ValidationError)
         } else {
             self.append_message(label, point.as_bytes());
             Ok(())