diff --git a/crypto/src/math/ec/custom/sec/SecP160R1Field.cs b/crypto/src/math/ec/custom/sec/SecP160R1Field.cs
new file mode 100644
index 000000000..6a5a2ef64
--- /dev/null
+++ b/crypto/src/math/ec/custom/sec/SecP160R1Field.cs
@@ -0,0 +1,186 @@
+using System;
+using System.Diagnostics;
+
+using Org.BouncyCastle.Math.Raw;
+
+namespace Org.BouncyCastle.Math.EC.Custom.Sec
+{
+ internal class SecP160R1Field
+ {
+ // 2^160 - 2^31 - 1
+ internal static readonly uint[] P = new uint[] { 0x7FFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF};
+ internal static readonly uint[] PExt = new uint[] { 0x00000001, 0x40000001, 0x00000000, 0x00000000, 0x00000000,
+ 0xFFFFFFFE, 0xFFFFFFFE, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF };
+ private static readonly uint[] PExtInv = new uint[]{ 0xFFFFFFFF, 0xBFFFFFFE, 0xFFFFFFFF, 0xFFFFFFFF,
+ 0xFFFFFFFF, 0x00000001, 0x00000001 };
+ private const uint P4 = 0xFFFFFFFF;
+ private const uint PExt9 = 0xFFFFFFFF;
+ private const uint PInv = 0x80000001;
+
+ public static void Add(uint[] x, uint[] y, uint[] z)
+ {
+ uint c = Nat160.Add(x, y, z);
+ if (c != 0 || (z[4] == P4 && Nat160.Gte(z, P)))
+ {
+ Nat.AddWordTo(5, PInv, z);
+ }
+ }
+
+ public static void AddExt(uint[] xx, uint[] yy, uint[] zz)
+ {
+ uint c = Nat.Add(10, xx, yy, zz);
+ if (c != 0 || (zz[9] == PExt9 && Nat.Gte(10, zz, PExt)))
+ {
+ if (Nat.AddTo(PExtInv.Length, PExtInv, zz) != 0)
+ {
+ Nat.IncAt(10, zz, PExtInv.Length);
+ }
+ }
+ }
+
+ public static void AddOne(uint[] x, uint[] z)
+ {
+ uint c = Nat.Inc(5, x, z);
+ if (c != 0 || (z[4] == P4 && Nat160.Gte(z, P)))
+ {
+ Nat.AddWordTo(5, PInv, z);
+ }
+ }
+
+ public static uint[] FromBigInteger(BigInteger x)
+ {
+ uint[] z = Nat160.FromBigInteger(x);
+ if (z[4] == P4 && Nat160.Gte(z, P))
+ {
+ Nat160.SubFrom(P, z);
+ }
+ return z;
+ }
+
+ public static void Half(uint[] x, uint[] z)
+ {
+ if ((x[0] & 1) == 0)
+ {
+ Nat.ShiftDownBit(5, x, 0, z);
+ }
+ else
+ {
+ uint c = Nat160.Add(x, P, z);
+ Nat.ShiftDownBit(5, z, c);
+ }
+ }
+
+ public static void Multiply(uint[] x, uint[] y, uint[] z)
+ {
+ uint[] tt = Nat160.CreateExt();
+ Nat160.Mul(x, y, tt);
+ Reduce(tt, z);
+ }
+
+ public static void MultiplyAddToExt(uint[] x, uint[] y, uint[] zz)
+ {
+ uint c = Nat160.MulAddTo(x, y, zz);
+ if (c != 0 || (zz[9] == PExt9 && Nat.Gte(10, zz, PExt)))
+ {
+ if (Nat.AddTo(PExtInv.Length, PExtInv, zz) != 0)
+ {
+ Nat.IncAt(10, zz, PExtInv.Length);
+ }
+ }
+ }
+
+ public static void Negate(uint[] x, uint[] z)
+ {
+ if (Nat160.IsZero(x))
+ {
+ Nat160.Zero(z);
+ }
+ else
+ {
+ Nat160.Sub(P, x, z);
+ }
+ }
+
+ public static void Reduce(uint[] xx, uint[] z)
+ {
+ ulong x5 = xx[5], x6 = xx[6], x7 = xx[7], x8 = xx[8], x9 = xx[9];
+
+ ulong c = 0;
+ c += (ulong)xx[0] + x5 + (x5 << 31);
+ z[0] = (uint)c; c >>= 32;
+ c += (ulong)xx[1] + x6 + (x6 << 31);
+ z[1] = (uint)c; c >>= 32;
+ c += (ulong)xx[2] + x7 + (x7 << 31);
+ z[2] = (uint)c; c >>= 32;
+ c += (ulong)xx[3] + x8 + (x8 << 31);
+ z[3] = (uint)c; c >>= 32;
+ c += (ulong)xx[4] + x9 + (x9 << 31);
+ z[4] = (uint)c; c >>= 32;
+
+ Debug.Assert(c >> 32 == 0);
+
+ Reduce32((uint)c, z);
+ }
+
+ public static void Reduce32(uint x, uint[] z)
+ {
+ if ((x != 0 && Nat160.MulWordsAdd(PInv, x, z, 0) != 0)
+ || (z[4] == P4 && Nat160.Gte(z, P)))
+ {
+ Nat.AddWordTo(5, PInv, z);
+ }
+ }
+
+ public static void Square(uint[] x, uint[] z)
+ {
+ uint[] tt = Nat160.CreateExt();
+ Nat160.Square(x, tt);
+ Reduce(tt, z);
+ }
+
+ public static void SquareN(uint[] x, int n, uint[] z)
+ {
+ Debug.Assert(n > 0);
+
+ uint[] tt = Nat160.CreateExt();
+ Nat160.Square(x, tt);
+ Reduce(tt, z);
+
+ while (--n > 0)
+ {
+ Nat160.Square(z, tt);
+ Reduce(tt, z);
+ }
+ }
+
+ public static void Subtract(uint[] x, uint[] y, uint[] z)
+ {
+ int c = Nat160.Sub(x, y, z);
+ if (c != 0)
+ {
+ Nat.SubWordFrom(5, PInv, z);
+ }
+ }
+
+ public static void SubtractExt(uint[] xx, uint[] yy, uint[] zz)
+ {
+ int c = Nat.Sub(10, xx, yy, zz);
+ if (c != 0)
+ {
+ if (Nat.SubFrom(PExtInv.Length, PExtInv, zz) != 0)
+ {
+ Nat.DecAt(10, zz, PExtInv.Length);
+ }
+ }
+ }
+
+ public static void Twice(uint[] x, uint[] z)
+ {
+ uint c = Nat.ShiftUpBit(5, x, 0, z);
+ if (c != 0 || (z[4] == P4 && Nat160.Gte(z, P)))
+ {
+ Nat.AddWordTo(5, PInv, z);
+ }
+ }
+ }
+}
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