diff --git a/crypto/src/math/ec/custom/sec/SecP128R1FieldElement.cs b/crypto/src/math/ec/custom/sec/SecP128R1FieldElement.cs
new file mode 100644
index 000000000..fa7951d5d
--- /dev/null
+++ b/crypto/src/math/ec/custom/sec/SecP128R1FieldElement.cs
@@ -0,0 +1,198 @@
+using System;
+
+using Org.BouncyCastle.Math.Raw;
+using Org.BouncyCastle.Utilities;
+
+namespace Org.BouncyCastle.Math.EC.Custom.Sec
+{
+ internal class SecP128R1FieldElement
+ : ECFieldElement
+ {
+ public static readonly BigInteger Q = SecP128R1Curve.q;
+
+ protected internal readonly uint[] x;
+
+ public SecP128R1FieldElement(BigInteger x)
+ {
+ if (x == null || x.SignValue < 0 || x.CompareTo(Q) >= 0)
+ throw new ArgumentException("value invalid for SecP128R1FieldElement", "x");
+
+ this.x = SecP128R1Field.FromBigInteger(x);
+ }
+
+ public SecP128R1FieldElement()
+ {
+ this.x = Nat128.Create();
+ }
+
+ protected internal SecP128R1FieldElement(uint[] x)
+ {
+ this.x = x;
+ }
+
+ public override bool IsZero
+ {
+ get { return Nat128.IsZero(x); }
+ }
+
+ public override bool IsOne
+ {
+ get { return Nat128.IsOne(x); }
+ }
+
+ public override bool TestBitZero()
+ {
+ return Nat128.GetBit(x, 0) == 1;
+ }
+
+ public override BigInteger ToBigInteger()
+ {
+ return Nat128.ToBigInteger(x);
+ }
+
+ public override string FieldName
+ {
+ get { return "SecP128R1Field"; }
+ }
+
+ public override int FieldSize
+ {
+ get { return Q.BitLength; }
+ }
+
+ public override ECFieldElement Add(ECFieldElement b)
+ {
+ uint[] z = Nat128.Create();
+ SecP128R1Field.Add(x, ((SecP128R1FieldElement)b).x, z);
+ return new SecP128R1FieldElement(z);
+ }
+
+ public override ECFieldElement AddOne()
+ {
+ uint[] z = Nat128.Create();
+ SecP128R1Field.AddOne(x, z);
+ return new SecP128R1FieldElement(z);
+ }
+
+ public override ECFieldElement Subtract(ECFieldElement b)
+ {
+ uint[] z = Nat128.Create();
+ SecP128R1Field.Subtract(x, ((SecP128R1FieldElement)b).x, z);
+ return new SecP128R1FieldElement(z);
+ }
+
+ public override ECFieldElement Multiply(ECFieldElement b)
+ {
+ uint[] z = Nat128.Create();
+ SecP128R1Field.Multiply(x, ((SecP128R1FieldElement)b).x, z);
+ return new SecP128R1FieldElement(z);
+ }
+
+ public override ECFieldElement Divide(ECFieldElement b)
+ {
+ // return multiply(b.invert());
+ uint[] z = Nat128.Create();
+ Mod.Invert(SecP128R1Field.P, ((SecP128R1FieldElement)b).x, z);
+ SecP128R1Field.Multiply(z, x, z);
+ return new SecP128R1FieldElement(z);
+ }
+
+ public override ECFieldElement Negate()
+ {
+ uint[] z = Nat128.Create();
+ SecP128R1Field.Negate(x, z);
+ return new SecP128R1FieldElement(z);
+ }
+
+ public override ECFieldElement Square()
+ {
+ uint[] z = Nat128.Create();
+ SecP128R1Field.Square(x, z);
+ return new SecP128R1FieldElement(z);
+ }
+
+ public override ECFieldElement Invert()
+ {
+ // return new SecP128R1FieldElement(toBigInteger().modInverse(Q));
+ uint[] z = Nat128.Create();
+ Mod.Invert(SecP128R1Field.P, x, z);
+ return new SecP128R1FieldElement(z);
+ }
+
+ // D.1.4 91
+ /**
+ * return a sqrt root - the routine verifies that the calculation returns the right value - if
+ * none exists it returns null.
+ */
+ public override ECFieldElement Sqrt()
+ {
+ /*
+ * Raise this element to the exponent 2^126 - 2^95
+ *
+ * Breaking up the exponent's binary representation into "repunits", we get:
+ * { 31 1s } { 95 0s }
+ *
+ * Therefore we need an addition chain containing 31 (the length of the repunit) We use:
+ * 1, 2, 4, 8, 10, 20, 30, [31]
+ */
+
+ uint[] x1 = this.x;
+ if (Nat128.IsZero(x1) || Nat128.IsOne(x1))
+ return this;
+
+ uint[] x2 = Nat128.Create();
+ SecP128R1Field.Square(x1, x2);
+ SecP128R1Field.Multiply(x2, x1, x2);
+ uint[] x4 = Nat128.Create();
+ SecP128R1Field.SquareN(x2, 2, x4);
+ SecP128R1Field.Multiply(x4, x2, x4);
+ uint[] x8 = Nat128.Create();
+ SecP128R1Field.SquareN(x4, 4, x8);
+ SecP128R1Field.Multiply(x8, x4, x8);
+ uint[] x10 = x4;
+ SecP128R1Field.SquareN(x8, 2, x10);
+ SecP128R1Field.Multiply(x10, x2, x10);
+ uint[] x20 = x2;
+ SecP128R1Field.SquareN(x10, 10, x20);
+ SecP128R1Field.Multiply(x20, x10, x20);
+ uint[] x30 = x8;
+ SecP128R1Field.SquareN(x20, 10, x30);
+ SecP128R1Field.Multiply(x30, x10, x30);
+ uint[] x31 = x10;
+ SecP128R1Field.Square(x30, x31);
+ SecP128R1Field.Multiply(x31, x1, x31);
+
+ uint[] t1 = x31;
+ SecP128R1Field.SquareN(t1, 95, t1);
+
+ uint[] t2 = x30;
+ SecP128R1Field.Square(t1, t2);
+
+ return Nat128.Eq(x1, t2) ? new SecP128R1FieldElement(t1) : null;
+ }
+
+ public override bool Equals(object obj)
+ {
+ return Equals(obj as SecP128R1FieldElement);
+ }
+
+ public override bool Equals(ECFieldElement other)
+ {
+ return Equals(other as SecP128R1FieldElement);
+ }
+
+ public virtual bool Equals(SecP128R1FieldElement other)
+ {
+ if (this == other)
+ return true;
+ if (null == other)
+ return false;
+ return Nat128.Eq(x, other.x);
+ }
+
+ public override int GetHashCode()
+ {
+ return Q.GetHashCode() ^ Arrays.GetHashCode(x, 0, 4);
+ }
+ }
+}
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