[zk-token-sdk] Add range proof generation error types (#34065)

* replace assert statements with `VectorLengthMismatch` error variant

* add a condition to check that the bit lengths are in the correct range

* replace assert statements with `GeneratorLengthMismatch`

* remove unchecked arithmetic

* add `InnerProductLengthMismatch` error

* fix typo

* add a clarifying comment on unwrap safety

* fix typo

zk-token-sdk/src/instruction/batched_range_proof/batched_range_proof_u128.rs

@@ -47,7 +47,7 @@ impl BatchedRangeProofU128Data {
             .try_fold(0_usize, |acc, &x| acc.checked_add(x))
             .ok_or(ProofGenerationError::IllegalAmountBitLength)?;
 
-        // `u64::BITS` is 128, which fits in a single byte and should not overflow to `usize` for
+        // `u128::BITS` is 128, which fits in a single byte and should not overflow to `usize` for
         // an overwhelming number of platforms. However, to be extra cautious, use `try_from` and
         // `unwrap` here. A simple case `u128::BITS as usize` can silently overflow.
         let expected_bit_length = usize::try_from(u128::BITS).unwrap();

zk-token-sdk/src/range_proof/errors.rs

@@ -5,6 +5,14 @@ use {crate::errors::TranscriptError, thiserror::Error};
 pub enum RangeProofGenerationError {
     #[error("maximum generator length exceeded")]
     MaximumGeneratorLengthExceeded,
+    #[error("amounts, commitments, openings, or bit lengths vectors have different lengths")]
+    VectorLengthMismatch,
+    #[error("invalid bit size")]
+    InvalidBitSize,
+    #[error("insufficient generators for the proof")]
+    GeneratorLengthMismatch,
+    #[error("inner product length mismatch")]
+    InnerProductLengthMismatch,
 }
 
 #[derive(Error, Clone, Debug, Eq, PartialEq)]
@@ -25,6 +33,8 @@ pub enum RangeProofVerificationError {
     InvalidGeneratorsLength,
     #[error("maximum generator length exceeded")]
     MaximumGeneratorLengthExceeded,
+    #[error("commitments and bit lengths vectors have different lengths")]
+    VectorLengthMismatch,
 }
 
 #[derive(Error, Clone, Debug, Eq, PartialEq)]

zk-token-sdk/src/range_proof/inner_product.rs

@@ -1,6 +1,9 @@
 use {
     crate::{
-        range_proof::{errors::RangeProofVerificationError, util},
+        range_proof::{
+            errors::{RangeProofGenerationError, RangeProofVerificationError},
+            util,
+        },
         transcript::TranscriptProtocol,
     },
     core::iter,
@@ -45,7 +48,7 @@ impl InnerProductProof {
         mut a_vec: Vec<Scalar>,
         mut b_vec: Vec<Scalar>,
         transcript: &mut Transcript,
-    ) -> Self {
+    ) -> Result<Self, RangeProofGenerationError> {
         // Create slices G, H, a, b backed by their respective
         // vectors.  This lets us reslice as we compress the lengths
         // of the vectors in the main loop below.
@@ -57,15 +60,20 @@ impl InnerProductProof {
         let mut n = G.len();
 
         // All of the input vectors must have the same length.
-        assert_eq!(G.len(), n);
-        assert_eq!(H.len(), n);
-        assert_eq!(a.len(), n);
-        assert_eq!(b.len(), n);
-        assert_eq!(G_factors.len(), n);
-        assert_eq!(H_factors.len(), n);
+        if G.len() != n
+            || H.len() != n
+            || a.len() != n
+            || b.len() != n
+            || G_factors.len() != n
+            || H_factors.len() != n
+        {
+            return Err(RangeProofGenerationError::GeneratorLengthMismatch);
+        }
 
         // All of the input vectors must have a length that is a power of two.
-        assert!(n.is_power_of_two());
+        if !n.is_power_of_two() {
+            return Err(RangeProofGenerationError::InvalidBitSize);
+        }
 
         transcript.innerproduct_domain_separator(n as u64);
 
@@ -76,18 +84,21 @@ impl InnerProductProof {
         // If it's the first iteration, unroll the Hprime = H*y_inv scalar mults
         // into multiscalar muls, for performance.
         if n != 1 {
-            n /= 2;
+            n = n.checked_div(2).unwrap();
             let (a_L, a_R) = a.split_at_mut(n);
             let (b_L, b_R) = b.split_at_mut(n);
             let (G_L, G_R) = G.split_at_mut(n);
             let (H_L, H_R) = H.split_at_mut(n);
 
-            let c_L = util::inner_product(a_L, b_R);
-            let c_R = util::inner_product(a_R, b_L);
+            let c_L = util::inner_product(a_L, b_R)
+                .ok_or(RangeProofGenerationError::InnerProductLengthMismatch)?;
+            let c_R = util::inner_product(a_R, b_L)
+                .ok_or(RangeProofGenerationError::InnerProductLengthMismatch)?;
 
             let L = RistrettoPoint::multiscalar_mul(
                 a_L.iter()
-                    .zip(G_factors[n..2 * n].iter())
+                    // `n` was previously divided in half and therefore, it cannot overflow.
+                    .zip(G_factors[n..n.checked_mul(2).unwrap()].iter())
                     .map(|(a_L_i, g)| a_L_i * g)
                     .chain(
                         b_R.iter()
@@ -105,7 +116,7 @@ impl InnerProductProof {
                     .map(|(a_R_i, g)| a_R_i * g)
                     .chain(
                         b_L.iter()
-                            .zip(H_factors[n..2 * n].iter())
+                            .zip(H_factors[n..n.checked_mul(2).unwrap()].iter())
                             .map(|(b_L_i, h)| b_L_i * h),
                     )
                     .chain(iter::once(c_R)),
@@ -126,11 +137,17 @@ impl InnerProductProof {
                 a_L[i] = a_L[i] * u + u_inv * a_R[i];
                 b_L[i] = b_L[i] * u_inv + u * b_R[i];
                 G_L[i] = RistrettoPoint::multiscalar_mul(
-                    &[u_inv * G_factors[i], u * G_factors[n + i]],
+                    &[
+                        u_inv * G_factors[i],
+                        u * G_factors[n.checked_add(i).unwrap()],
+                    ],
                     &[G_L[i], G_R[i]],
                 );
                 H_L[i] = RistrettoPoint::multiscalar_mul(
-                    &[u * H_factors[i], u_inv * H_factors[n + i]],
+                    &[
+                        u * H_factors[i],
+                        u_inv * H_factors[n.checked_add(i).unwrap()],
+                    ],
                     &[H_L[i], H_R[i]],
                 )
             }
@@ -142,14 +159,16 @@ impl InnerProductProof {
         }
 
         while n != 1 {
-            n /= 2;
+            n = n.checked_div(2).unwrap();
             let (a_L, a_R) = a.split_at_mut(n);
             let (b_L, b_R) = b.split_at_mut(n);
             let (G_L, G_R) = G.split_at_mut(n);
             let (H_L, H_R) = H.split_at_mut(n);
 
-            let c_L = util::inner_product(a_L, b_R);
-            let c_R = util::inner_product(a_R, b_L);
+            let c_L = util::inner_product(a_L, b_R)
+                .ok_or(RangeProofGenerationError::InnerProductLengthMismatch)?;
+            let c_R = util::inner_product(a_R, b_L)
+                .ok_or(RangeProofGenerationError::InnerProductLengthMismatch)?;
 
             let L = RistrettoPoint::multiscalar_mul(
                 a_L.iter().chain(b_R.iter()).chain(iter::once(&c_L)),
@@ -185,12 +204,12 @@ impl InnerProductProof {
             H = H_L;
         }
 
-        InnerProductProof {
+        Ok(InnerProductProof {
             L_vec,
             R_vec,
             a: a[0],
             b: b[0],
-        }
+        })
     }
 
     /// Computes three vectors of verification scalars \\([u\_{i}^{2}]\\), \\([u\_{i}^{-2}]\\) and
@@ -210,7 +229,7 @@ impl InnerProductProof {
             // and this check prevents overflow in 1<<lg_n below.
             return Err(RangeProofVerificationError::InvalidBitSize);
         }
-        if n != (1 << lg_n) {
+        if n != (1_usize.checked_shl(lg_n as u32).unwrap()) {
             return Err(RangeProofVerificationError::InvalidBitSize);
         }
 
@@ -244,11 +263,14 @@ impl InnerProductProof {
         let mut s = Vec::with_capacity(n);
         s.push(allinv);
         for i in 1..n {
-            let lg_i = (32 - 1 - (i as u32).leading_zeros()) as usize;
-            let k = 1 << lg_i;
+            let lg_i = 31_u32.checked_sub((i as u32).leading_zeros()).unwrap() as usize;
+            let k = 1_usize.checked_shl(lg_i as u32).unwrap();
             // The challenges are stored in "creation order" as [u_k,...,u_1],
             // so u_{lg(i)+1} = is indexed by (lg_n-1) - lg_i
-            let u_lg_i_sq = challenges_sq[(lg_n - 1) - lg_i];
+            let u_lg_i_sq = challenges_sq[lg_n
+                .checked_sub(1)
+                .and_then(|x| x.checked_sub(lg_i))
+                .unwrap()];
             s.push(s[i - k] * u_lg_i_sq);
         }
 
@@ -418,7 +440,7 @@ mod tests {
 
         let a: Vec<_> = (0..n).map(|_| Scalar::random(&mut OsRng)).collect();
         let b: Vec<_> = (0..n).map(|_| Scalar::random(&mut OsRng)).collect();
-        let c = util::inner_product(&a, &b);
+        let c = util::inner_product(&a, &b).unwrap();
 
         let G_factors: Vec<Scalar> = iter::repeat(Scalar::one()).take(n).collect();
 
@@ -451,7 +473,8 @@ mod tests {
             a.clone(),
             b.clone(),
             &mut prover_transcript,
-        );
+        )
+        .unwrap();
 
         assert!(proof
             .verify(

zk-token-sdk/src/range_proof/mod.rs

@@ -75,12 +75,23 @@ impl RangeProof {
     ) -> Result<Self, RangeProofGenerationError> {
         // amounts, bit-lengths, openings must be same length vectors
         let m = amounts.len();
-        assert_eq!(bit_lengths.len(), m);
-        assert_eq!(openings.len(), m);
+        if bit_lengths.len() != m || openings.len() != m {
+            return Err(RangeProofGenerationError::VectorLengthMismatch);
+        }
+
+        // each bit length must be greater than 0 for the proof to make sense
+        if bit_lengths
+            .iter()
+            .any(|bit_length| *bit_length == 0 || *bit_length > u64::BITS as usize)
+        {
+            return Err(RangeProofGenerationError::InvalidBitSize);
+        }
 
         // total vector dimension to compute the ultimate inner product proof for
         let nm: usize = bit_lengths.iter().sum();
-        assert!(nm.is_power_of_two());
+        if !nm.is_power_of_two() {
+            return Err(RangeProofGenerationError::VectorLengthMismatch);
+        }
 
         let bp_gens = BulletproofGens::new(nm)
             .map_err(|_| RangeProofGenerationError::MaximumGeneratorLengthExceeded)?;
@@ -93,7 +104,10 @@ impl RangeProof {
         for (amount_i, n_i) in amounts.iter().zip(bit_lengths.iter()) {
             for j in 0..(*n_i) {
                 let (G_ij, H_ij) = gens_iter.next().unwrap();
-                let v_ij = Choice::from(((amount_i >> j) & 1) as u8);
+
+                // `j` is guaranteed to be at most `u64::BITS` (a 6-bit number) and therefore,
+                // casting is lossless and right shift can be safely unwrapped
+                let v_ij = Choice::from((amount_i.checked_shr(j as u32).unwrap() & 1) as u8);
                 let mut point = -H_ij;
                 point.conditional_assign(G_ij, v_ij);
                 A += point;
@@ -138,7 +152,9 @@ impl RangeProof {
             let mut exp_2 = Scalar::one();
 
             for j in 0..(*n_i) {
-                let a_L_j = Scalar::from((amount_i >> j) & 1);
+                // `j` is guaranteed to be at most `u64::BITS` (a 6-bit number) and therefore,
+                // casting is lossless and right shift can be safely unwrapped
+                let a_L_j = Scalar::from(amount_i.checked_shr(j as u32).unwrap() & 1);
                 let a_R_j = a_L_j - Scalar::one();
 
                 l_poly.0[i] = a_L_j - z;
@@ -148,13 +164,17 @@ impl RangeProof {
 
                 exp_y *= y;
                 exp_2 = exp_2 + exp_2;
-                i += 1;
+
+                // `i` is capped by the sum of vectors in `bit_lengths`
+                i = i.checked_add(1).unwrap();
             }
             exp_z *= z;
         }
 
         // define t(x) = <l(x), r(x)> = t_0 + t_1*x + t_2*x
-        let t_poly = l_poly.inner_product(&r_poly);
+        let t_poly = l_poly
+            .inner_product(&r_poly)
+            .ok_or(RangeProofGenerationError::InnerProductLengthMismatch)?;
 
         // generate Pedersen commitment for the coefficients t_1 and t_2
         let (T_1, t_1_blinding) = Pedersen::new(t_poly.1);
@@ -216,7 +236,7 @@ impl RangeProof {
             l_vec,
             r_vec,
             transcript,
-        );
+        )?;
 
         Ok(RangeProof {
             A,
@@ -238,7 +258,9 @@ impl RangeProof {
         transcript: &mut Transcript,
     ) -> Result<(), RangeProofVerificationError> {
         // commitments and bit-lengths must be same length vectors
-        assert_eq!(comms.len(), bit_lengths.len());
+        if comms.len() != bit_lengths.len() {
+            return Err(RangeProofVerificationError::VectorLengthMismatch);
+        }
 
         let m = bit_lengths.len();
         let nm: usize = bit_lengths.iter().sum();

zk-token-sdk/src/range_proof/util.rs

@@ -11,20 +11,20 @@ impl VecPoly1 {
         VecPoly1(vec![Scalar::zero(); n], vec![Scalar::zero(); n])
     }
 
-    pub fn inner_product(&self, rhs: &VecPoly1) -> Poly2 {
+    pub fn inner_product(&self, rhs: &VecPoly1) -> Option<Poly2> {
         // Uses Karatsuba's method
         let l = self;
         let r = rhs;
 
-        let t0 = inner_product(&l.0, &r.0);
-        let t2 = inner_product(&l.1, &r.1);
+        let t0 = inner_product(&l.0, &r.0)?;
+        let t2 = inner_product(&l.1, &r.1)?;
 
         let l0_plus_l1 = add_vec(&l.0, &l.1);
         let r0_plus_r1 = add_vec(&r.0, &r.1);
 
-        let t1 = inner_product(&l0_plus_l1, &r0_plus_r1) - t0 - t2;
+        let t1 = inner_product(&l0_plus_l1, &r0_plus_r1)? - t0 - t2;
 
-        Poly2(t0, t1, t2)
+        Some(Poly2(t0, t1, t2))
     }
 
     pub fn eval(&self, x: Scalar) -> Vec<Scalar> {
@@ -98,16 +98,16 @@ pub fn read32(data: &[u8]) -> [u8; 32] {
 /// \\[
 ///    {\langle {\mathbf{a}}, {\mathbf{b}} \rangle} = \sum\_{i=0}^{n-1} a\_i \cdot b\_i.
 /// \\]
-/// Panics if the lengths of \\(\mathbf{a}\\) and \\(\mathbf{b}\\) are not equal.
-pub fn inner_product(a: &[Scalar], b: &[Scalar]) -> Scalar {
+/// Errors if the lengths of \\(\mathbf{a}\\) and \\(\mathbf{b}\\) are not equal.
+pub fn inner_product(a: &[Scalar], b: &[Scalar]) -> Option<Scalar> {
     let mut out = Scalar::zero();
     if a.len() != b.len() {
-        panic!("inner_product(a,b): lengths of vectors do not match");
+        return None;
     }
     for i in 0..a.len() {
         out += a[i] * b[i];
     }
-    out
+    Some(out)
 }
 
 /// Takes the sum of all the powers of `x`, up to `n`