crypto: add scalar mult functions returning ge_p3 instead of ge_p2

ge_scalarmult_p3
ge_double_scalarmult_precomp_vartime2_p3
ge_double_scalarmult_base_vartime_p3

This makes it possible to reuse the result without having to
convert back to unsigned char[32] and back to ge types.

2 files changed, 155 insertions, 0 deletions

diff --git a/src/crypto/crypto-ops.c b/src/crypto/crypto-ops.c
index b5c62bce4..f8e767875 100644
--- a/src/crypto/crypto-ops.c
+++ b/src/crypto/crypto-ops.c
@@ -1234,6 +1234,51 @@ void ge_double_scalarmult_base_vartime(ge_p2 *r, const unsigned char *a, const g
   }
 }
 
+void ge_double_scalarmult_base_vartime_p3(ge_p3 *r3, const unsigned char *a, const ge_p3 *A, const unsigned char *b) {
+  signed char aslide[256];
+  signed char bslide[256];
+  ge_dsmp Ai; /* A, 3A, 5A, 7A, 9A, 11A, 13A, 15A */
+  ge_p1p1 t;
+  ge_p3 u;
+  ge_p2 r;
+  int i;
+
+  slide(aslide, a);
+  slide(bslide, b);
+  ge_dsm_precomp(Ai, A);
+
+  ge_p2_0(&r);
+
+  for (i = 255; i >= 0; --i) {
+    if (aslide[i] || bslide[i]) break;
+  }
+
+  for (; i >= 0; --i) {
+    ge_p2_dbl(&t, &r);
+
+    if (aslide[i] > 0) {
+      ge_p1p1_to_p3(&u, &t);
+      ge_add(&t, &u, &Ai[aslide[i]/2]);
+    } else if (aslide[i] < 0) {
+      ge_p1p1_to_p3(&u, &t);
+      ge_sub(&t, &u, &Ai[(-aslide[i])/2]);
+    }
+
+    if (bslide[i] > 0) {
+      ge_p1p1_to_p3(&u, &t);
+      ge_madd(&t, &u, &ge_Bi[bslide[i]/2]);
+    } else if (bslide[i] < 0) {
+      ge_p1p1_to_p3(&u, &t);
+      ge_msub(&t, &u, &ge_Bi[(-bslide[i])/2]);
+    }
+
+    if (i == 0)
+      ge_p1p1_to_p3(r3, &t);
+    else
+      ge_p1p1_to_p2(&r, &t);
+  }
+}
+
 /* From ge_frombytes.c, modified */
 
 int ge_frombytes_vartime(ge_p3 *h, const unsigned char *s) {
@@ -2000,6 +2045,70 @@ void ge_scalarmult(ge_p2 *r, const unsigned char *a, const ge_p3 *A) {
   }
 }
 
+void ge_scalarmult_p3(ge_p3 *r3, const unsigned char *a, const ge_p3 *A) {
+  signed char e[64];
+  int carry, carry2, i;
+  ge_cached Ai[8]; /* 1 * A, 2 * A, ..., 8 * A */
+  ge_p1p1 t;
+  ge_p3 u;
+  ge_p2 r;
+
+  carry = 0; /* 0..1 */
+  for (i = 0; i < 31; i++) {
+    carry += a[i]; /* 0..256 */
+    carry2 = (carry + 8) >> 4; /* 0..16 */
+    e[2 * i] = carry - (carry2 << 4); /* -8..7 */
+    carry = (carry2 + 8) >> 4; /* 0..1 */
+    e[2 * i + 1] = carry2 - (carry << 4); /* -8..7 */
+  }
+  carry += a[31]; /* 0..128 */
+  carry2 = (carry + 8) >> 4; /* 0..8 */
+  e[62] = carry - (carry2 << 4); /* -8..7 */
+  e[63] = carry2; /* 0..8 */
+
+  ge_p3_to_cached(&Ai[0], A);
+  for (i = 0; i < 7; i++) {
+    ge_add(&t, A, &Ai[i]);
+    ge_p1p1_to_p3(&u, &t);
+    ge_p3_to_cached(&Ai[i + 1], &u);
+  }
+
+  ge_p2_0(&r);
+  for (i = 63; i >= 0; i--) {
+    signed char b = e[i];
+    unsigned char bnegative = negative(b);
+    unsigned char babs = b - (((-bnegative) & b) << 1);
+    ge_cached cur, minuscur;
+    ge_p2_dbl(&t, &r);
+    ge_p1p1_to_p2(&r, &t);
+    ge_p2_dbl(&t, &r);
+    ge_p1p1_to_p2(&r, &t);
+    ge_p2_dbl(&t, &r);
+    ge_p1p1_to_p2(&r, &t);
+    ge_p2_dbl(&t, &r);
+    ge_p1p1_to_p3(&u, &t);
+    ge_cached_0(&cur);
+    ge_cached_cmov(&cur, &Ai[0], equal(babs, 1));
+    ge_cached_cmov(&cur, &Ai[1], equal(babs, 2));
+    ge_cached_cmov(&cur, &Ai[2], equal(babs, 3));
+    ge_cached_cmov(&cur, &Ai[3], equal(babs, 4));
+    ge_cached_cmov(&cur, &Ai[4], equal(babs, 5));
+    ge_cached_cmov(&cur, &Ai[5], equal(babs, 6));
+    ge_cached_cmov(&cur, &Ai[6], equal(babs, 7));
+    ge_cached_cmov(&cur, &Ai[7], equal(babs, 8));
+    fe_copy(minuscur.YplusX, cur.YminusX);
+    fe_copy(minuscur.YminusX, cur.YplusX);
+    fe_copy(minuscur.Z, cur.Z);
+    fe_neg(minuscur.T2d, cur.T2d);
+    ge_cached_cmov(&cur, &minuscur, bnegative);
+    ge_add(&t, &u, &cur);
+    if (i == 0)
+      ge_p1p1_to_p3(r3, &t);
+    else
+      ge_p1p1_to_p2(&r, &t);
+  }
+}
+
 void ge_double_scalarmult_precomp_vartime2(ge_p2 *r, const unsigned char *a, const ge_dsmp Ai, const unsigned char *b, const ge_dsmp Bi) {
   signed char aslide[256];
   signed char bslide[256];
@@ -2039,6 +2148,49 @@ void ge_double_scalarmult_precomp_vartime2(ge_p2 *r, const unsigned char *a, con
   }
 }
 
+void ge_double_scalarmult_precomp_vartime2_p3(ge_p3 *r3, const unsigned char *a, const ge_dsmp Ai, const unsigned char *b, const ge_dsmp Bi) {
+  signed char aslide[256];
+  signed char bslide[256];
+  ge_p1p1 t;
+  ge_p3 u;
+  ge_p2 r;
+  int i;
+
+  slide(aslide, a);
+  slide(bslide, b);
+
+  ge_p2_0(&r);
+
+  for (i = 255; i >= 0; --i) {
+    if (aslide[i] || bslide[i]) break;
+  }
+
+  for (; i >= 0; --i) {
+    ge_p2_dbl(&t, &r);
+
+    if (aslide[i] > 0) {
+      ge_p1p1_to_p3(&u, &t);
+      ge_add(&t, &u, &Ai[aslide[i]/2]);
+    } else if (aslide[i] < 0) {
+      ge_p1p1_to_p3(&u, &t);
+      ge_sub(&t, &u, &Ai[(-aslide[i])/2]);
+    }
+
+    if (bslide[i] > 0) {
+      ge_p1p1_to_p3(&u, &t);
+      ge_add(&t, &u, &Bi[bslide[i]/2]);
+    } else if (bslide[i] < 0) {
+      ge_p1p1_to_p3(&u, &t);
+      ge_sub(&t, &u, &Bi[(-bslide[i])/2]);
+    }
+
+    if (i == 0)
+      ge_p1p1_to_p3(r3, &t);
+    else
+      ge_p1p1_to_p2(&r, &t);
+  }
+}
+
 void ge_double_scalarmult_precomp_vartime(ge_p2 *r, const unsigned char *a, const ge_p3 *A, const unsigned char *b, const ge_dsmp Bi) {
   ge_dsmp Ai; /* A, 3A, 5A, 7A, 9A, 11A, 13A, 15A */
 
diff --git a/src/crypto/crypto-ops.h b/src/crypto/crypto-ops.h
index c76455551..dd0337bc0 100644
--- a/src/crypto/crypto-ops.h
+++ b/src/crypto/crypto-ops.h
@@ -79,6 +79,7 @@ typedef ge_cached ge_dsmp[8];
 extern const ge_precomp ge_Bi[8];
 void ge_dsm_precomp(ge_dsmp r, const ge_p3 *s);
 void ge_double_scalarmult_base_vartime(ge_p2 *, const unsigned char *, const ge_p3 *, const unsigned char *);
+void ge_double_scalarmult_base_vartime_p3(ge_p3 *, const unsigned char *, const ge_p3 *, const unsigned char *);
 
 /* From ge_frombytes.c, modified */
 
@@ -127,8 +128,10 @@ void sc_reduce(unsigned char *);
 /* New code */
 
 void ge_scalarmult(ge_p2 *, const unsigned char *, const ge_p3 *);
+void ge_scalarmult_p3(ge_p3 *, const unsigned char *, const ge_p3 *);
 void ge_double_scalarmult_precomp_vartime(ge_p2 *, const unsigned char *, const ge_p3 *, const unsigned char *, const ge_dsmp);
 void ge_double_scalarmult_precomp_vartime2(ge_p2 *, const unsigned char *, const ge_dsmp, const unsigned char *, const ge_dsmp);
+void ge_double_scalarmult_precomp_vartime2_p3(ge_p3 *, const unsigned char *, const ge_dsmp, const unsigned char *, const ge_dsmp);
 void ge_mul8(ge_p1p1 *, const ge_p2 *);
 extern const fe fe_ma2;
 extern const fe fe_ma;