4 files changed, 35 insertions, 4 deletions
diff --git a/src/crypto/crypto-ops-data.c b/src/crypto/crypto-ops-data.c
index 4ff4310de..1f77513ca 100644
--- a/src/crypto/crypto-ops-data.c
+++ b/src/crypto/crypto-ops-data.c
@@ -871,3 +871,9 @@ const fe fe_fffb2 = {8166131, -6741800, -17040804, 3154616, 21461005, 1466302, -
 const fe fe_fffb3 = {-13620103, 14639558, 4532995, 7679154, 16815101, -15883539, -22863840, -14813421, 13716513, -6477756}; /* sqrt(-sqrt(-1) * A * (A + 2)) */
 const fe fe_fffb4 = {-21786234, -12173074, 21573800, 4524538, -4645904, 16204591, 8012863, -8444712, 3212926, 6885324}; /* sqrt(sqrt(-1) * A * (A + 2)) */
 const ge_p3 ge_p3_identity = { {0}, {1, 0}, {1, 0}, {0} };
+const ge_p3 ge_p3_H = {
+  {7329926, -15101362, 31411471, 7614783, 27996851, -3197071, -11157635, -6878293, 466949, -7986503},
+  {5858699, 5096796, 21321203, -7536921, -5553480, -11439507, -5627669, 15045946, 19977121, 5275251},
+  {1, 0, 0, 0, 0, 0, 0, 0, 0, 0},
+  {23443568, -5110398, -8776029, -4345135, 6889568, -14710814, 7474843, 3279062, 14550766, -7453428}
+};
diff --git a/src/crypto/crypto-ops.c b/src/crypto/crypto-ops.c
index 45d412ac6..09296d6f9 100644
--- a/src/crypto/crypto-ops.c
+++ b/src/crypto/crypto-ops.c
@@ -3707,9 +3707,8 @@ void sc_muladd(unsigned char *s, const unsigned char *a, const unsigned char *b,
   s[31] = s11 >> 17;
 }
 
-/* Assumes that a != INT64_MIN */
 static int64_t signum(int64_t a) {
-  return (a >> 63) - ((-a) >> 63);
+  return a > 0 ? 1 : a < 0 ? -1 : 0;
 }
 
 int sc_check(const unsigned char *s) {
@@ -3730,3 +3729,16 @@ int sc_isnonzero(const unsigned char *s) {
     s[18] | s[19] | s[20] | s[21] | s[22] | s[23] | s[24] | s[25] | s[26] |
     s[27] | s[28] | s[29] | s[30] | s[31]) - 1) >> 8) + 1;
 }
+
+int ge_p3_is_point_at_infinity(const ge_p3 *p) {
+  // X = 0 and Y == Z
+  int n;
+  for (n = 0; n < 10; ++n)
+  {
+    if (p->X[n] | p->T[n])
+      return 0;
+    if (p->Y[n] != p->Z[n])
+      return 0;
+  }
+  return 1;
+}
diff --git a/src/crypto/crypto-ops.h b/src/crypto/crypto-ops.h
index dc3c60794..2910dafd4 100644
--- a/src/crypto/crypto-ops.h
+++ b/src/crypto/crypto-ops.h
@@ -140,6 +140,7 @@ extern const fe fe_fffb2;
 extern const fe fe_fffb3;
 extern const fe fe_fffb4;
 extern const ge_p3 ge_p3_identity;
+extern const ge_p3 ge_p3_H;
 void ge_fromfe_frombytes_vartime(ge_p2 *, const unsigned char *);
 void sc_0(unsigned char *);
 void sc_reduce32(unsigned char *);
@@ -158,3 +159,5 @@ void ge_sub(ge_p1p1 *r, const ge_p3 *p, const ge_cached *q);
 void fe_add(fe h, const fe f, const fe g);
 void fe_tobytes(unsigned char *, const fe);
 void fe_invert(fe out, const fe z);
+
+int ge_p3_is_point_at_infinity(const ge_p3 *p);
diff --git a/src/crypto/crypto.cpp b/src/crypto/crypto.cpp
index 4243c71fd..ad7721cf0 100644
--- a/src/crypto/crypto.cpp
+++ b/src/crypto/crypto.cpp
@@ -116,7 +116,7 @@ namespace crypto {
     do
     {
       generate_random_bytes_thread_safe(32, bytes);
-    } while (!less32(bytes, limit)); // should be good about 15/16 of the time
+    } while (!sc_isnonzero(bytes) && !less32(bytes, limit)); // should be good about 15/16 of the time
     sc_reduce32(bytes);
   }
   /* generate a random 32-byte (256-bit) integer and copy it to res */
@@ -274,11 +274,18 @@ namespace crypto {
 #endif
     buf.h = prefix_hash;
     buf.key = pub;
+  try_again:
     random_scalar(k);
+    if (((const uint32_t*)(&k))[7] == 0) // we don't want tiny numbers here
+      goto try_again;
     ge_scalarmult_base(&tmp3, &k);
     ge_p3_tobytes(&buf.comm, &tmp3);
     hash_to_scalar(&buf, sizeof(s_comm), sig.c);
+    if (!sc_isnonzero((const unsigned char*)sig.c.data))
+      goto try_again;
     sc_mulsub(&sig.r, &sig.c, &unwrap(sec), &k);
+    if (!sc_isnonzero((const unsigned char*)sig.r.data))
+      goto try_again;
   }
 
   bool crypto_ops::check_signature(const hash &prefix_hash, const public_key &pub, const signature &sig) {
@@ -292,11 +299,14 @@ namespace crypto {
     if (ge_frombytes_vartime(&tmp3, &pub) != 0) {
       return false;
     }
-    if (sc_check(&sig.c) != 0 || sc_check(&sig.r) != 0) {
+    if (sc_check(&sig.c) != 0 || sc_check(&sig.r) != 0 || !sc_isnonzero(&sig.c)) {
       return false;
     }
     ge_double_scalarmult_base_vartime(&tmp2, &sig.c, &tmp3, &sig.r);
     ge_tobytes(&buf.comm, &tmp2);
+    static const ec_point infinity = {{ 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}};
+    if (memcmp(&buf.comm, &infinity, 32) == 0)
+      return false;
     hash_to_scalar(&buf, sizeof(s_comm), c);
     sc_sub(&c, &c, &sig.c);
     return sc_isnonzero(&c) == 0;