ec suite_b: Hide COMMON_OPS.n and reduce direct use of .num_limbs.

src/ec/suite_b/ecdh.rs

@@ -183,7 +183,7 @@ mod tests {
             // getting that value from the PRNG.
             let mut n_bytes = [0u8; ec::SCALAR_MAX_BYTES];
             let num_bytes = curve.elem_scalar_seed_len;
-            limb::big_endian_from_limbs(&ops.n.limbs[..ops.num_limbs], &mut n_bytes[..num_bytes]);
+            limb::big_endian_from_limbs(ops.n_limbs(), &mut n_bytes[..num_bytes]);
             {
                 let n_bytes = &mut n_bytes[..num_bytes];
                 let rng = test::rand::FixedSliceRandom { bytes: n_bytes };

src/ec/suite_b/ecdsa/verification.rs

@@ -157,10 +157,7 @@ impl EcdsaVerificationAlgorithm {
             return Ok(());
         }
         if self.ops.elem_less_than(&r, &self.ops.q_minus_n) {
-            self.ops
-                .scalar_ops
-                .common
-                .elem_add(&mut r, &public_key_ops.common.n);
+            self.ops.scalar_ops.common.elem_add(&mut r, self.ops.n());
             if sig_r_equals_x(self.ops, &r, &x, &z2) {
                 return Ok(());
             }

src/ec/suite_b/ops.rs

@@ -54,7 +54,7 @@ impl Point {
 pub struct CommonOps {
     pub num_limbs: usize,
     q: Modulus,
-    pub n: Elem<Unencoded>,
+    n: Elem<Unencoded>,
 
     pub a: Elem<R>, // Must be -3 mod q
     pub b: Elem<R>,
@@ -73,6 +73,11 @@ impl CommonOps {
         self.num_limbs * LIMB_BYTES
     }
 
+    #[cfg(test)]
+    pub(super) fn n_limbs(&self) -> &[Limb] {
+        &self.n.limbs[..self.num_limbs]
+    }
+
     #[inline]
     pub fn elem_add<E: Encoding>(&self, a: &mut Elem<E>, b: &Elem<E>) {
         let num_limbs = self.num_limbs;
@@ -280,6 +285,10 @@ pub struct PublicScalarOps {
 }
 
 impl PublicScalarOps {
+    pub fn n(&self) -> &Elem<Unencoded> {
+        &self.scalar_ops.common.n
+    }
+
     #[inline]
     pub fn scalar_as_elem(&self, a: &Scalar) -> Elem<Unencoded> {
         Elem {