Port custom curve for secp256k1 from Java

1 files changed, 142 insertions, 0 deletions

diff --git a/crypto/src/math/ec/custom/sec/SecP256K1Field.cs b/crypto/src/math/ec/custom/sec/SecP256K1Field.cs
new file mode 100644
index 000000000..ec2c36e9f
--- /dev/null
+++ b/crypto/src/math/ec/custom/sec/SecP256K1Field.cs
@@ -0,0 +1,142 @@
+using System;
+using System.Diagnostics;
+
+namespace Org.BouncyCastle.Math.EC.Custom.Sec
+{
+    internal class SecP256K1Field
+    {
+        // 2^256 - 2^32 - 2^9 - 2^8 - 2^7 - 2^6 - 2^4 - 1
+        internal static readonly uint[] P = new uint[]{ 0xFFFFFC2F, 0xFFFFFFFE, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF,
+            0xFFFFFFFF, 0xFFFFFFFF };
+        private const uint P7 = 0xFFFFFFFF;
+        private static readonly uint[] PExt = new uint[]{ 0x000E90A1, 0x000007A2, 0x00000001, 0x00000000, 0x00000000,
+            0x00000000, 0x00000000, 0x00000000, 0xFFFFF85E, 0xFFFFFFFD, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF,
+            0xFFFFFFFF, 0xFFFFFFFF };
+        private const uint PExt15 = 0xFFFFFFFF;
+        private static readonly ulong PInv = 0x00000001000003D1UL;
+
+        public static void Add(uint[] x, uint[] y, uint[] z)
+        {
+            uint c = Nat256.Add(x, y, z);
+            if (c != 0 || (z[7] == P7 && Nat256.Gte(z, P)))
+            {
+                Nat256.AddDWord(PInv, z, 0);
+            }
+        }
+
+        public static void AddExt(uint[] xx, uint[] yy, uint[] zz)
+        {
+            uint c = Nat256.AddExt(xx, yy, zz);
+            if (c != 0 || (zz[15] == PExt15 && Nat256.GteExt(zz, PExt)))
+            {
+                Nat256.SubExt(zz, PExt, zz);
+            }
+        }
+
+        public static void AddOne(uint[] x, uint[] z)
+        {
+            Array.Copy(x, 0, z, 0, 8);
+            uint c = Nat256.Inc(z, 0);
+            if (c != 0 || (z[7] == P7 && Nat256.Gte(z, P)))
+            {
+                Nat256.AddDWord(PInv, z, 0);
+            }
+        }
+
+        public static uint[] FromBigInteger(BigInteger x)
+        {
+            uint[] z = Nat256.FromBigInteger(x);
+            if (z[7] == P7 && Nat256.Gte(z, P))
+            {
+                Nat256.AddDWord(PInv, z, 0);
+            }
+            return z;
+        }
+
+        public static void Half(uint[] x, uint[] z)
+        {
+            if ((x[0] & 1) == 0)
+            {
+                Nat256.ShiftDownBit(x, 0, z);
+            }
+            else
+            {
+                uint c = Nat256.Add(x, P, z);
+                Nat256.ShiftDownBit(z, c, z);
+            }
+        }
+
+        public static void Multiply(uint[] x, uint[] y, uint[] z)
+        {
+            uint[] tt = Nat256.CreateExt();
+            Nat256.Mul(x, y, tt);
+            Reduce(tt, z);
+        }
+
+        public static void Negate(uint[] x, uint[] z)
+        {
+            if (Nat256.IsZero(x))
+            {
+                Nat256.Zero(z);
+            }
+            else
+            {
+                Nat256.Sub(P, x, z);
+            }
+        }
+
+        public static void Reduce(uint[] tt, uint[] z)
+        {
+            long extra = -(long)tt[8];
+            extra += (long)Nat256.MulWordAddExt((uint)PInv, tt, 8, tt, 0);
+            extra += (long)Nat256.AddToExt(tt, 8, tt, 1) << 32;
+            extra += (long)tt[8];
+
+            ulong c = Nat256.MulWordDwordAdd((uint)PInv, (ulong)extra, tt, 0);
+            c += Nat256.AddDWord((ulong)extra, tt, 1);
+
+            Debug.Assert(c == 0 || c == 1);
+
+            if (c != 0 || (tt[7] == P7 && Nat256.Gte(tt, P)))
+            {
+                Nat256.AddDWord(PInv, tt, 0);
+            }
+
+            Array.Copy(tt, 0, z, 0, 8);
+        }
+
+        public static void Square(uint[] x, uint[] z)
+        {
+            uint[] tt = Nat256.CreateExt();
+            Nat256.Square(x, tt);
+            Reduce(tt, z);
+        }
+
+        public static void Subtract(uint[] x, uint[] y, uint[] z)
+        {
+            int c = Nat256.Sub(x, y, z);
+            if (c != 0)
+            {
+                Nat256.SubDWord(PInv, z);
+            }
+        }
+
+        public static void SubtractExt(uint[] xx, uint[] yy, uint[] zz)
+        {
+            int c = Nat256.SubExt(xx, yy, zz);
+            if (c != 0)
+            {
+                Nat256.AddExt(zz, PExt, zz);
+            }
+        }
+
+        public static void Twice(uint[] x, uint[] z)
+        {
+            uint c = Nat256.ShiftUpBit(x, 0, z);
+            if (c != 0 || (z[7] == P7 && Nat256.Gte(z, P)))
+            {
+                Nat256.AddDWord(PInv, z, 0);
+            }
+        }
+    }
+}