ec: Simplify some internal parsing APIs.

src/ec/suite_b/ops/mod.rs

@@ -351,7 +351,7 @@ impl PublicKeyOps {
     ) -> Result<Elem<R>, error::Unspecified> {
         let _cpu = cpu::features();
         let encoded_value = input.read_bytes(self.common.len())?;
-        let parsed = elem_parse_big_endian_fixed_consttime(q, encoded_value)?;
+        let parsed = parse_big_endian_fixed_consttime(q, encoded_value, AllowZero::Yes)?;
         let mut r = Elem::zero();
         let rr = Elem::from(&self.common.q.rr);
         // Montgomery encode (elem_to_mont).
@@ -534,22 +534,6 @@ fn elem_sqr_mul_acc(
     ops.elem_mul(acc, b, cpu)
 }
 
-#[inline]
-pub(super) fn elem_parse_big_endian_fixed_consttime(
-    q: &Modulus<Q>,
-    bytes: untrusted::Input,
-) -> Result<Elem<Unencoded>, error::Unspecified> {
-    parse_big_endian_fixed_consttime(q, bytes, AllowZero::Yes)
-}
-
-#[inline]
-pub(super) fn scalar_parse_big_endian_fixed_consttime(
-    n: &Modulus<N>,
-    bytes: untrusted::Input,
-) -> Result<Scalar, error::Unspecified> {
-    parse_big_endian_fixed_consttime(n, bytes, AllowZero::No)
-}
-
 #[inline]
 pub(super) fn scalar_parse_big_endian_variable(
     n: &Modulus<N>,
@@ -583,7 +567,7 @@ pub(super) fn scalar_parse_big_endian_partially_reduced_variable_consttime(
     Ok(r)
 }
 
-fn parse_big_endian_fixed_consttime<M>(
+pub(super) fn parse_big_endian_fixed_consttime<M>(
     m: &Modulus<M>,
     bytes: untrusted::Input,
     allow_zero: AllowZero,
@@ -863,9 +847,9 @@ mod tests {
         test::run(test_file, |section, test_case| {
             assert_eq!(section, "");
 
-            let mut a = consume_elem(q, test_case, "a");
-            let b = consume_elem(q, test_case, "b");
-            let r = consume_elem(q, test_case, "r");
+            let mut a = consume_elem_mont(q, test_case, "a");
+            let b = consume_elem_mont(q, test_case, "b");
+            let r = consume_elem_mont(q, test_case, "r");
             q.elem_mul(&mut a, &b);
             assert_limbs_are_equal(ops, &a.limbs, &r.limbs);
 
@@ -1298,7 +1282,8 @@ mod tests {
         let num_limbs = q.num_limbs.into();
         let bytes = test::from_hex(elems[i]).unwrap();
         let bytes = untrusted::Input::from(&bytes);
-        let r: Elem<Unencoded> = elem_parse_big_endian_fixed_consttime(q, bytes).unwrap();
+        let r: Elem<Unencoded> =
+            parse_big_endian_fixed_consttime(q, bytes, AllowZero::Yes).unwrap();
         // XXX: “Transmute” this to `Elem<R>` limbs.
         limbs_out[(i * num_limbs)..((i + 1) * num_limbs)].copy_from_slice(&r.limbs[..num_limbs]);
     }
@@ -1318,7 +1303,7 @@ mod tests {
             let bytes = test::from_hex(elems[i]).unwrap();
             let bytes = untrusted::Input::from(&bytes);
             let unencoded: Elem<Unencoded> =
-                elem_parse_big_endian_fixed_consttime(q, bytes).unwrap();
+                parse_big_endian_fixed_consttime(q, bytes, AllowZero::Yes).unwrap();
             // XXX: “Transmute” this to `Elem<R>` limbs.
             Elem {
                 limbs: unencoded.limbs,
@@ -1365,13 +1350,17 @@ mod tests {
         }
     }
 
-    fn consume_elem(q: &Modulus<Q>, test_case: &mut test::TestCase, name: &str) -> Elem<R> {
+    fn consume_elem(q: &Modulus<Q>, test_case: &mut test::TestCase, name: &str) -> Elem<Unencoded> {
         let unpadded_bytes = test_case.consume_bytes(name);
         let mut bytes = vec![0; q.bytes_len() - unpadded_bytes.len()];
         bytes.extend(&unpadded_bytes);
 
         let bytes = untrusted::Input::from(&bytes);
-        let r: Elem<Unencoded> = elem_parse_big_endian_fixed_consttime(q, bytes).unwrap();
+        parse_big_endian_fixed_consttime(q, bytes, AllowZero::Yes).unwrap()
+    }
+
+    fn consume_elem_mont(q: &Modulus<Q>, test_case: &mut test::TestCase, name: &str) -> Elem<R> {
+        let r = consume_elem(q, test_case, name);
         // XXX: “Transmute” this to an `Elem<R>`.
         Elem {
             limbs: r.limbs,
@@ -1391,9 +1380,7 @@ mod tests {
         test_case: &mut test::TestCase,
         name: &str,
     ) -> Scalar<R> {
-        let bytes = test_case.consume_bytes(name);
-        let bytes = untrusted::Input::from(&bytes);
-        let s = scalar_parse_big_endian_variable(n, AllowZero::Yes, bytes).unwrap();
+        let s = consume_scalar(n, test_case, name);
         // “Transmute” it to a `Scalar<R>`.
         Scalar {
             limbs: s.limbs,

src/ec/suite_b/private_key.rs

@@ -16,7 +16,12 @@
 //! ECDSA signing).
 
 use super::{ops::*, verify_affine_point_is_on_the_curve};
-use crate::{arithmetic::montgomery::R, cpu, ec, error, limb, rand};
+use crate::{
+    arithmetic::montgomery::R,
+    cpu, ec, error,
+    limb::{self, AllowZero},
+    rand,
+};
 
 /// Generates a random scalar in the range [1, n).
 pub(super) fn random_scalar(
@@ -125,7 +130,7 @@ pub(super) fn scalar_from_big_endian_bytes(
     // way, we avoid needing to compute or store the value (n - 1), we avoid the
     // need to implement a function to add one to a scalar, and we avoid needing
     // to convert the scalar back into an array of bytes.
-    scalar_parse_big_endian_fixed_consttime(n, untrusted::Input::from(bytes))
+    parse_big_endian_fixed_consttime(n, untrusted::Input::from(bytes), AllowZero::No)
 }
 
 pub(super) fn public_from_private(