ec/suite_b: Make more LeakyLimb->Limb conversions explicit.

Rename `Modulus` to `PublicModulus` and add a new `Modulus`:

    PublicModulus::limbs: [LeakyLimb; _]
    Modulus::limbs: [Limb; _]

Refactor the callers to (approximately) minimize the number of
types a `Modulus` is constructed, as it will require a copy if/when
`Limb` becomes a type distinct from `LeakyLimb`.

mk/generate_curves.py

@@ -33,7 +33,7 @@
 
 use super::{
     elem::{binary_op, binary_op_assign},
-    elem_sqr_mul, elem_sqr_mul_acc, Modulus, *,
+    elem_sqr_mul, elem_sqr_mul_acc, PublicModulus, *,
 };
 
 pub(super) const NUM_LIMBS: usize = (%(bits)d + LIMB_BITS - 1) / LIMB_BITS;
@@ -42,9 +42,9 @@
     num_limbs: elem::NumLimbs::P%(bits)s,
     order_bits: %(bits)d,
 
-    q: Modulus {
+    q: PublicModulus {
         p: limbs_from_hex("%(q)x"),
-        rr: limbs_from_hex(%(q_rr)s),
+        rr: PublicElem::from_hex(%(q_rr)s),
     },
     n: PublicElem::from_hex("%(n)x"),
 

src/ec/suite_b.rs

@@ -31,10 +31,12 @@ use crate::{arithmetic::montgomery::*, cpu, ec, error, io::der, pkcs8};
 //
 fn verify_affine_point_is_on_the_curve(
     ops: &CommonOps,
+    q: &Modulus<Q>,
     (x, y): (&Elem<R>, &Elem<R>),
 ) -> Result<(), error::Unspecified> {
     verify_affine_point_is_on_the_curve_scaled(
         ops,
+        q,
         (x, y),
         &Elem::from(&ops.a),
         &Elem::from(&ops.b),
@@ -52,6 +54,7 @@ fn verify_affine_point_is_on_the_curve(
 // This function also verifies that the point is not at infinity.
 fn verify_jacobian_point_is_on_the_curve(
     ops: &CommonOps,
+    q: &Modulus<Q>,
     p: &Point,
 ) -> Result<Elem<R>, error::Unspecified> {
     let z = ops.point_z(p);
@@ -109,7 +112,7 @@ fn verify_jacobian_point_is_on_the_curve(
     let z4_a = ops.elem_product(&z4, &Elem::from(&ops.a));
     let z6 = ops.elem_product(&z4, &z2);
     let z6_b = ops.elem_product(&z6, &Elem::from(&ops.b));
-    verify_affine_point_is_on_the_curve_scaled(ops, (&x, &y), &z4_a, &z6_b)?;
+    verify_affine_point_is_on_the_curve_scaled(ops, q, (&x, &y), &z4_a, &z6_b)?;
     Ok(z2)
 }
 
@@ -140,16 +143,17 @@ fn verify_jacobian_point_is_on_the_curve(
 // Jean-Pierre Seifert.
 fn verify_affine_point_is_on_the_curve_scaled(
     ops: &CommonOps,
+    q: &Modulus<Q>,
     (x, y): (&Elem<R>, &Elem<R>),
     a_scaled: &Elem<R>,
     b_scaled: &Elem<R>,
 ) -> Result<(), error::Unspecified> {
     let lhs = ops.elem_squared(y);
 
     let mut rhs = ops.elem_squared(x);
-    ops.elem_add(&mut rhs, a_scaled);
+    q.elem_add(&mut rhs, a_scaled);
     ops.elem_mul(&mut rhs, x);
-    ops.elem_add(&mut rhs, b_scaled);
+    q.elem_add(&mut rhs, b_scaled);
 
     if !ops.elems_are_equal(&lhs, &rhs).leak() {
         return Err(error::Unspecified);

src/ec/suite_b/ecdh.rs

@@ -93,6 +93,8 @@ fn ecdh(
     // The "NSA Guide" steps are from section 3.1 of the NSA guide, "Ephemeral
     // Unified Model."
 
+    let q = public_key_ops.common.elem_modulus();
+
     // NSA Guide Step 1 is handled separately.
 
     // NIST SP 800-56Ar2 5.6.2.2.2.
@@ -101,7 +103,7 @@ fn ecdh(
     // `parse_uncompressed_point` verifies that the point is not at infinity
     // and that it is on the curve, using the Partial Public-Key Validation
     // Routine.
-    let peer_public_key = parse_uncompressed_point(public_key_ops, peer_public_key, cpu)?;
+    let peer_public_key = parse_uncompressed_point(public_key_ops, &q, peer_public_key, cpu)?;
 
     // NIST SP 800-56Ar2 Step 1.
     // NSA Guide Step 3 (except point at infinity check).
@@ -134,7 +136,7 @@ fn ecdh(
     // `big_endian_affine_from_jacobian` verifies that the result is not at
     // infinity and also does an extra check to verify that the point is on
     // the curve.
-    big_endian_affine_from_jacobian(private_key_ops, out, None, &product, cpu)
+    big_endian_affine_from_jacobian(private_key_ops, &q, out, None, &product, cpu)
 
     // NSA Guide Step 5 & 6 are deferred to the caller. Again, we have a
     // pretty liberal interpretation of the NIST's spec's "Destroy" that

src/ec/suite_b/ecdsa/digest_scalar.rs

@@ -42,30 +42,27 @@ use crate::{digest, ec::suite_b::ops::*};
 /// right will give a value less than 2**255, which is less than `n`. The
 /// analogous argument applies for P-384. However, it does *not* apply in
 /// general; for example, it doesn't apply to P-521.
-pub fn digest_scalar(ops: &ScalarOps, msg: digest::Digest) -> Scalar {
-    digest_scalar_(ops, msg.as_ref())
+pub fn digest_scalar(ops: &ScalarOps, n: &Modulus<N>, msg: digest::Digest) -> Scalar {
+    digest_scalar_(ops, n, msg.as_ref())
 }
 
 #[cfg(test)]
-pub(crate) fn digest_bytes_scalar(ops: &ScalarOps, digest: &[u8]) -> Scalar {
-    digest_scalar_(ops, digest)
+pub(crate) fn digest_bytes_scalar(ops: &ScalarOps, n: &Modulus<N>, digest: &[u8]) -> Scalar {
+    digest_scalar_(ops, n, digest)
 }
 
 // This is a separate function solely so that we can test specific digest
 // values like all-zero values and values larger than `n`.
-fn digest_scalar_(ops: &ScalarOps, digest: &[u8]) -> Scalar {
+fn digest_scalar_(ops: &ScalarOps, n: &Modulus<N>, digest: &[u8]) -> Scalar {
     let len = ops.scalar_bytes_len();
     let digest = if digest.len() > len {
         &digest[..len]
     } else {
         digest
     };
 
-    scalar_parse_big_endian_partially_reduced_variable_consttime(
-        ops.common,
-        untrusted::Input::from(digest),
-    )
-    .unwrap()
+    scalar_parse_big_endian_partially_reduced_variable_consttime(n, untrusted::Input::from(digest))
+        .unwrap()
 }
 
 #[cfg(test)]
@@ -94,6 +91,7 @@ mod tests {
                         panic!("Unsupported curve+digest: {}+{}", curve_name, digest_name);
                     }
                 };
+                let n = ops.scalar_ops.scalar_modulus();
 
                 assert_eq!(input.len(), digest_alg.output_len());
                 assert_eq!(output.len(), ops.scalar_ops.scalar_bytes_len());
@@ -105,7 +103,7 @@ mod tests {
                 )
                 .unwrap();
 
-                let actual = digest_bytes_scalar(ops.scalar_ops, &input);
+                let actual = digest_bytes_scalar(ops.scalar_ops, &n, &input);
                 assert_eq!(
                     ops.scalar_ops.leak_limbs(&actual),
                     ops.scalar_ops.leak_limbs(&expected)

src/ec/suite_b/ecdsa/signing.rs

@@ -238,6 +238,8 @@ impl EcdsaKeyPair {
         let scalar_ops = ops.scalar_ops;
         let cops = scalar_ops.common;
         let private_key_ops = self.alg.private_key_ops;
+        let q = cops.elem_modulus();
+        let n = scalar_ops.scalar_modulus();
 
         for _ in 0..100 {
             // XXX: iteration conut?
@@ -250,9 +252,9 @@ impl EcdsaKeyPair {
 
             // Step 3.
             let r = {
-                let (x, _) = private_key::affine_from_jacobian(private_key_ops, &r, cpu)?;
+                let (x, _) = private_key::affine_from_jacobian(private_key_ops, &q, &r, cpu)?;
                 let x = cops.elem_unencoded(&x);
-                elem_reduced_to_scalar(cops, &x)
+                n.elem_reduced_to_scalar(&x)
             };
             if cops.is_zero(&r) {
                 continue;
@@ -261,12 +263,12 @@ impl EcdsaKeyPair {
             // Step 4 is done by the caller.
 
             // Step 5.
-            let e = digest_scalar(scalar_ops, h);
+            let e = digest_scalar(scalar_ops, &n, h);
 
             // Step 6.
             let s = {
-                let dr = scalar_ops.scalar_product(&self.d, &r, cpu);
-                let e_plus_dr = scalar_sum(cops, &e, dr);
+                let mut e_plus_dr = scalar_ops.scalar_product(&self.d, &r, cpu);
+                n.elem_add(&mut e_plus_dr, &e);
                 scalar_ops.scalar_product(&k_inv, &e_plus_dr, cpu)
             };
             if cops.is_zero(&s) {

src/ec/suite_b/ecdsa/verification.rs

@@ -63,7 +63,8 @@ impl signature::VerificationAlgorithm for EcdsaVerificationAlgorithm {
 
             // NSA Guide Step 3: "Convert the bit string H to an integer e as
             // described in Appendix B.2."
-            digest_scalar(self.ops.scalar_ops, h)
+            let n = self.ops.scalar_ops.scalar_modulus();
+            digest_scalar(self.ops.scalar_ops, &n, h)
         };
 
         self.verify_digest(public_key, e, signature)
@@ -84,6 +85,7 @@ impl EcdsaVerificationAlgorithm {
 
         let public_key_ops = self.ops.public_key_ops;
         let scalar_ops = self.ops.scalar_ops;
+        let q = public_key_ops.common.elem_modulus();
 
         // NSA Guide Prerequisites:
         //
@@ -102,7 +104,7 @@ impl EcdsaVerificationAlgorithm {
         // can do. Prerequisite #2 is handled implicitly as the domain
         // parameters are hard-coded into the source. Prerequisite #3 is
         // handled by `parse_uncompressed_point`.
-        let peer_pub_key = parse_uncompressed_point(public_key_ops, public_key, cpu)?;
+        let peer_pub_key = parse_uncompressed_point(public_key_ops, &q, public_key, cpu)?;
 
         let (r, s) = signature.read_all(error::Unspecified, |input| {
             (self.split_rs)(scalar_ops, input)
@@ -134,7 +136,7 @@ impl EcdsaVerificationAlgorithm {
         // `verify_affine_point_is_on_the_curve_scaled` for details on why).
         // But, we're going to avoid converting to affine for performance
         // reasons, so we do the verification using the Jacobian coordinates.
-        let z2 = verify_jacobian_point_is_on_the_curve(public_key_ops.common, &product)?;
+        let z2 = verify_jacobian_point_is_on_the_curve(public_key_ops.common, &q, &product)?;
 
         // NSA Guide Step 7: "Compute v = xR mod n."
         // NSA Guide Step 8: "Compare v and r0. If v = r0, output VALID;
@@ -158,9 +160,9 @@ impl EcdsaVerificationAlgorithm {
         if sig_r_equals_x(self.ops, &r, &x, &z2) {
             return Ok(());
         }
-        if self.ops.elem_less_than_vartime(&r, &self.ops.q_minus_n) {
+        if q.elem_less_than_vartime(&r, &self.ops.q_minus_n) {
             let n = Elem::from(self.ops.n());
-            self.ops.scalar_ops.common.elem_add(&mut r, &n);
+            q.elem_add(&mut r, &n);
             if sig_r_equals_x(self.ops, &r, &x, &z2) {
                 return Ok(());
             }
@@ -316,9 +318,11 @@ mod tests {
                         panic!("Unsupported curve: {}", curve_name);
                     }
                 };
+                let n = alg.ops.scalar_ops.scalar_modulus();
 
                 let digest = super::super::digest_scalar::digest_bytes_scalar(
                     alg.ops.scalar_ops,
+                    &n,
                     &digest[..],
                 );
                 let actual_result = alg.verify_digest(