diff --git a/crypto/src/math/ec/custom/sec/SecP224K1Field.cs b/crypto/src/math/ec/custom/sec/SecP224K1Field.cs
new file mode 100644
index 000000000..edc938d22
--- /dev/null
+++ b/crypto/src/math/ec/custom/sec/SecP224K1Field.cs
@@ -0,0 +1,150 @@
+using System;
+using System.Diagnostics;
+
+namespace Org.BouncyCastle.Math.EC.Custom.Sec
+{
+ internal class SecP224K1Field
+ {
+ // 2^224 - 2^32 - 2^12 - 2^11 - 2^9 - 2^7 - 2^4 - 2 - 1
+ internal static readonly uint[] P = new uint[]{ 0xFFFFE56D, 0xFFFFFFFE, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF,
+ 0xFFFFFFFF };
+ private const uint P6 = 0xFFFFFFFF;
+ private static readonly uint[] PExt = new uint[]{ 0x02C23069, 0x00003526, 0x00000001, 0x00000000, 0x00000000,
+ 0x00000000, 0x00000000, 0xFFFFCADA, 0xFFFFFFFD, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF };
+ private const uint PExt13 = 0xFFFFFFFF;
+ private const ulong PInv = 0x0000000100001A93L;
+ private const uint PInv33 = 0x1A93;
+
+ public static void Add(uint[] x, uint[] y, uint[] z)
+ {
+ uint c = Nat224.Add(x, y, z);
+ if (c != 0 || (z[6] == P6 && Nat224.Gte(z, P)))
+ {
+ Nat224.AddDWord(PInv, z, 0);
+ }
+ }
+
+ public static void AddExt(uint[] xx, uint[] yy, uint[] zz)
+ {
+ uint c = Nat224.AddExt(xx, yy, zz);
+ if (c != 0 || (zz[13] == PExt13 && Nat224.GteExt(zz, PExt)))
+ {
+ Nat224.SubExt(zz, PExt, zz);
+ }
+ }
+
+ public static void AddOne(uint[] x, uint[] z)
+ {
+ Array.Copy(x, 0, z, 0, 8);
+ uint c = Nat224.Inc(z, 0);
+ if (c != 0 || (z[6] == P6 && Nat224.Gte(z, P)))
+ {
+ Nat224.AddDWord(PInv, z, 0);
+ }
+ }
+
+ public static uint[] FromBigInteger(BigInteger x)
+ {
+ uint[] z = Nat224.FromBigInteger(x);
+ if (z[6] == P6 && Nat224.Gte(z, P))
+ {
+ Nat224.AddDWord(PInv, z, 0);
+ }
+ return z;
+ }
+
+ public static void Half(uint[] x, uint[] z)
+ {
+ if ((x[0] & 1) == 0)
+ {
+ Nat224.ShiftDownBit(x, 0, z);
+ }
+ else
+ {
+ uint c = Nat224.Add(x, P, z);
+ Nat224.ShiftDownBit(z, c, z);
+ }
+ }
+
+ public static void Multiply(uint[] x, uint[] y, uint[] z)
+ {
+ uint[] tt = Nat224.CreateExt();
+ Nat224.Mul(x, y, tt);
+ Reduce(tt, z);
+ }
+
+ public static void Negate(uint[] x, uint[] z)
+ {
+ if (Nat224.IsZero(x))
+ {
+ Nat224.Zero(z);
+ }
+ else
+ {
+ Nat224.Sub(P, x, z);
+ }
+ }
+
+ public static void Reduce(uint[] xx, uint[] z)
+ {
+ ulong c = Nat224.Mul33Add(PInv33, xx, 7, xx, 0, z, 0);
+ c = Nat224.Mul33DWordAdd(PInv33, c, z, 0);
+
+ Debug.Assert(c == 0 || c == 1);
+
+ if (c != 0 || (z[6] == P6 && Nat224.Gte(z, P)))
+ {
+ Nat224.AddDWord(PInv, z, 0);
+ }
+ }
+
+ public static void Square(uint[] x, uint[] z)
+ {
+ uint[] tt = Nat224.CreateExt();
+ Nat224.Square(x, tt);
+ Reduce(tt, z);
+ }
+
+ public static void SquareN(uint[] x, int n, uint[] z)
+ {
+ Debug.Assert(n > 0);
+
+ uint[] tt = Nat224.CreateExt();
+ Nat224.Square(x, tt);
+ Reduce(tt, z);
+
+ while (--n > 0)
+ {
+ Nat224.Square(z, tt);
+ Reduce(tt, z);
+ }
+ }
+
+ public static void Subtract(uint[] x, uint[] y, uint[] z)
+ {
+ int c = Nat224.Sub(x, y, z);
+ if (c != 0)
+ {
+ Nat224.SubDWord(PInv, z);
+ }
+ }
+
+ public static void SubtractExt(uint[] xx, uint[] yy, uint[] zz)
+ {
+ int c = Nat224.SubExt(xx, yy, zz);
+ if (c != 0)
+ {
+ Nat224.AddExt(zz, PExt, zz);
+ }
+ }
+
+ public static void Twice(uint[] x, uint[] z)
+ {
+ uint c = Nat224.ShiftUpBit(x, 0, z);
+ if (c != 0 || (z[6] == P6 && Nat224.Gte(z, P)))
+ {
+ Nat224.AddDWord(PInv, z, 0);
+ }
+ }
+ }
+}
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