2 files changed, 102 insertions, 0 deletions
diff --git a/src/crypto/crypto-ops.c b/src/crypto/crypto-ops.c
index 3110d3ce7..508709280 100644
--- a/src/crypto/crypto-ops.c
+++ b/src/crypto/crypto-ops.c
@@ -1234,6 +1234,56 @@ void ge_double_scalarmult_base_vartime(ge_p2 *r, const unsigned char *a, const g
   }
 }
 
+// Computes aG + bB + cC (G is the fixed basepoint)
+void ge_triple_scalarmult_base_vartime(ge_p2 *r, const unsigned char *a, const unsigned char *b, const ge_dsmp Bi, const unsigned char *c, const ge_dsmp Ci) {
+  signed char aslide[256];
+  signed char bslide[256];
+  signed char cslide[256];
+  ge_p1p1 t;
+  ge_p3 u;
+  int i;
+
+  slide(aslide, a);
+  slide(bslide, b);
+  slide(cslide, c);
+
+  ge_p2_0(r);
+
+  for (i = 255; i >= 0; --i) {
+    if (aslide[i] || bslide[i] || cslide[i]) break;
+  }
+
+  for (; i >= 0; --i) {
+    ge_p2_dbl(&t, r);
+
+    if (aslide[i] > 0) {
+      ge_p1p1_to_p3(&u, &t);
+      ge_madd(&t, &u, &ge_Bi[aslide[i]/2]);
+    } else if (aslide[i] < 0) {
+      ge_p1p1_to_p3(&u, &t);
+      ge_msub(&t, &u, &ge_Bi[(-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 (cslide[i] > 0) {
+      ge_p1p1_to_p3(&u, &t);
+      ge_add(&t, &u, &Ci[cslide[i]/2]);
+    } else if (cslide[i] < 0) {
+      ge_p1p1_to_p3(&u, &t);
+      ge_sub(&t, &u, &Ci[(-cslide[i])/2]);
+    }
+
+    ge_p1p1_to_p2(r, &t);
+  }
+}
+
 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];
@@ -2148,6 +2198,56 @@ void ge_double_scalarmult_precomp_vartime2(ge_p2 *r, const unsigned char *a, con
   }
 }
 
+// Computes aA + bB + cC (all points require precomputation)
+void ge_triple_scalarmult_precomp_vartime(ge_p2 *r, const unsigned char *a, const ge_dsmp Ai, const unsigned char *b, const ge_dsmp Bi, const unsigned char *c, const ge_dsmp Ci) {
+  signed char aslide[256];
+  signed char bslide[256];
+  signed char cslide[256];
+  ge_p1p1 t;
+  ge_p3 u;
+  int i;
+
+  slide(aslide, a);
+  slide(bslide, b);
+  slide(cslide, c);
+
+  ge_p2_0(r);
+
+  for (i = 255; i >= 0; --i) {
+    if (aslide[i] || bslide[i] || cslide[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 (cslide[i] > 0) {
+      ge_p1p1_to_p3(&u, &t);
+      ge_add(&t, &u, &Ci[cslide[i]/2]);
+    } else if (cslide[i] < 0) {
+      ge_p1p1_to_p3(&u, &t);
+      ge_sub(&t, &u, &Ci[(-cslide[i])/2]);
+    }
+
+    ge_p1p1_to_p2(r, &t);
+  }
+}
+
 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];
diff --git a/src/crypto/crypto-ops.h b/src/crypto/crypto-ops.h
index eeb94669b..22f76974b 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_triple_scalarmult_base_vartime(ge_p2 *, const unsigned char *, const unsigned char *, const ge_dsmp, const unsigned char *, const ge_dsmp);
 void ge_double_scalarmult_base_vartime_p3(ge_p3 *, const unsigned char *, const ge_p3 *, const unsigned char *);
 
 /* From ge_frombytes.c, modified */
@@ -130,6 +131,7 @@ void sc_reduce(unsigned char *);
 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_triple_scalarmult_precomp_vartime(ge_p2 *, const unsigned char *, const ge_dsmp, const unsigned char *, const ge_dsmp, 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 *);