EC updates from bc-java

- use half-trace when possible (odd m) for decompression/validation
- provide field-specific half-trace methods for custom curves
- clarify the logic of point-order testing for binary curves
- expand test cases for invalid points

1 files changed, 22 insertions, 0 deletions

diff --git a/crypto/src/math/ec/custom/sec/SecT131Field.cs b/crypto/src/math/ec/custom/sec/SecT131Field.cs
index 248b1969e..db703d9e0 100644
--- a/crypto/src/math/ec/custom/sec/SecT131Field.cs
+++ b/crypto/src/math/ec/custom/sec/SecT131Field.cs
@@ -35,11 +35,33 @@ namespace Org.BouncyCastle.Math.EC.Custom.Sec
             z[2] = x[2];
         }
 
+        private static void AddTo(ulong[] x, ulong[] z)
+        {
+            z[0] ^= x[0];
+            z[1] ^= x[1];
+            z[2] ^= x[2];
+        }
+
         public static ulong[] FromBigInteger(BigInteger x)
         {
             return Nat.FromBigInteger64(131, x);
         }
 
+        public static void HalfTrace(ulong[] x, ulong[] z)
+        {
+            ulong[] tt = Nat.Create64(5);
+
+            Nat192.Copy64(x, z);
+            for (int i = 1; i < 131; i += 2)
+            {
+                ImplSquare(z, tt);
+                Reduce(tt, z);
+                ImplSquare(z, tt);
+                Reduce(tt, z);
+                AddTo(x, z);
+            }
+        }
+
         public static void Invert(ulong[] x, ulong[] z)
         {
             if (Nat192.IsZero64(x))