Merge pull request #266

3f3964e Add specific VERIFY tests for _fe_cmov (Peter Dettman)
a0601cd Fix VERIFY calculations in _fe_cmov methods (Peter Dettman)

src/field_10x26_impl.h

@@ -1083,8 +1083,10 @@ static SECP256K1_INLINE void secp256k1_fe_cmov(secp256k1_fe_t *r, const secp256k
     r->n[8] = (r->n[8] & mask0) | (a->n[8] & mask1);
     r->n[9] = (r->n[9] & mask0) | (a->n[9] & mask1);
 #ifdef VERIFY
-    r->magnitude = (r->magnitude & mask0) | (a->magnitude & mask1);
-    r->normalized = (r->normalized & mask0) | (a->normalized & mask1);
+    if (a->magnitude > r->magnitude) {
+        r->magnitude = a->magnitude;
+    }
+    r->normalized &= a->normalized;
 #endif
 }
 

src/field_5x52_impl.h

@@ -414,8 +414,10 @@ static SECP256K1_INLINE void secp256k1_fe_cmov(secp256k1_fe_t *r, const secp256k
     r->n[3] = (r->n[3] & mask0) | (a->n[3] & mask1);
     r->n[4] = (r->n[4] & mask0) | (a->n[4] & mask1);
 #ifdef VERIFY
-    r->magnitude = (r->magnitude & mask0) | (a->magnitude & mask1);
-    r->normalized = (r->normalized & mask0) | (a->normalized & mask1);
+    if (a->magnitude > r->magnitude) {
+        r->magnitude = a->magnitude;
+    }
+    r->normalized &= a->normalized;
 #endif
 }
 

src/tests.c

@@ -47,9 +47,7 @@ void random_field_element_magnitude(secp256k1_fe_t *fe) {
     secp256k1_fe_negate(&zero, &zero, 0);
     secp256k1_fe_mul_int(&zero, n - 1);
     secp256k1_fe_add(fe, &zero);
-#ifdef VERIFY
-    CHECK(fe->magnitude == n);
-#endif
+    VERIFY_CHECK(fe->magnitude == n);
 }
 
 void random_group_element_test(secp256k1_ge_t *ge) {
@@ -737,13 +735,22 @@ void run_field_convert(void) {
     CHECK(memcmp(&fes2, &fes, sizeof(fes)) == 0);
 }
 
+int fe_memcmp(const secp256k1_fe_t *a, const secp256k1_fe_t *b) {
+    secp256k1_fe_t t = *b;
+#ifdef VERIFY
+    t.magnitude = a->magnitude;
+    t.normalized = a->normalized;
+#endif
+    return memcmp(a, &t, sizeof(secp256k1_fe_t));
+}
+
 void run_field_misc(void) {
     secp256k1_fe_t x;
     secp256k1_fe_t y;
     secp256k1_fe_t z;
     secp256k1_fe_t q;
     secp256k1_fe_t fe5 = SECP256K1_FE_CONST(0, 0, 0, 0, 0, 0, 0, 5);
-    int i;
+    int i, j;
     for (i = 0; i < 5*count; i++) {
         secp256k1_fe_storage_t xs, ys, zs;
         random_fe(&x);
@@ -756,14 +763,27 @@ void run_field_misc(void) {
         /* Test fe conditional move; z is not normalized here. */
         q = x;
         secp256k1_fe_cmov(&x, &z, 0);
+        VERIFY_CHECK(!x.normalized && x.magnitude == z.magnitude);
         secp256k1_fe_cmov(&x, &x, 1);
-        CHECK(memcmp(&x, &z, sizeof(x)) != 0);
-        CHECK(memcmp(&x, &q, sizeof(x)) == 0);
+        CHECK(fe_memcmp(&x, &z) != 0);
+        CHECK(fe_memcmp(&x, &q) == 0);
         secp256k1_fe_cmov(&q, &z, 1);
-        CHECK(memcmp(&q, &z, sizeof(q)) == 0);
-        /* Test storage conversion and conditional moves. */
-        secp256k1_fe_normalize(&z);
+        VERIFY_CHECK(!q.normalized && q.magnitude == z.magnitude);
+        CHECK(fe_memcmp(&q, &z) == 0);
+        secp256k1_fe_normalize_var(&x);
+        secp256k1_fe_normalize_var(&z);
         CHECK(!secp256k1_fe_equal_var(&x, &z));
+        secp256k1_fe_normalize_var(&q);
+        secp256k1_fe_cmov(&q, &z, (i&1));
+        VERIFY_CHECK(q.normalized && q.magnitude == 1);
+        for (j = 0; j < 6; j++) {
+            secp256k1_fe_negate(&z, &z, j+1);
+            secp256k1_fe_normalize_var(&q);
+            secp256k1_fe_cmov(&q, &z, (j&1));
+            VERIFY_CHECK(!q.normalized && q.magnitude == (j+2));
+        }
+        secp256k1_fe_normalize_var(&z);
+        /* Test storage conversion and conditional moves. */
         secp256k1_fe_to_storage(&xs, &x);
         secp256k1_fe_to_storage(&ys, &y);
         secp256k1_fe_to_storage(&zs, &z);
@@ -1661,7 +1681,7 @@ void test_ecdsa_end_to_end(void) {
     extra[31] = 0;
     extra[0] = 1;
     CHECK(secp256k1_ecdsa_sign(ctx, message, signature4, &signaturelen4, privkey, NULL, extra) == 1);
-    CHECK(signaturelen3 > 0);
+    CHECK(signaturelen4 > 0);
     CHECK((signaturelen != signaturelen2) || (memcmp(signature, signature2, signaturelen) != 0));
     CHECK((signaturelen != signaturelen3) || (memcmp(signature, signature3, signaturelen) != 0));
     CHECK((signaturelen3 != signaturelen2) || (memcmp(signature3, signature2, signaturelen3) != 0));