1 files changed, 102 insertions, 0 deletions
diff --git a/crypto/src/asn1/x9/X9FieldID.cs b/crypto/src/asn1/x9/X9FieldID.cs
new file mode 100644
index 000000000..c51cc4df2
--- /dev/null
+++ b/crypto/src/asn1/x9/X9FieldID.cs
@@ -0,0 +1,102 @@
+using Org.BouncyCastle.Math;
+
+namespace Org.BouncyCastle.Asn1.X9
+{
+    /**
+     * ASN.1 def for Elliptic-Curve Field ID structure. See
+     * X9.62, for further details.
+     */
+    public class X9FieldID
+        : Asn1Encodable
+    {
+        private readonly DerObjectIdentifier	id;
+        private readonly Asn1Object parameters;
+
+		/**
+		 * Constructor for elliptic curves over prime fields
+		 * <code>F<sub>2</sub></code>.
+		 * @param primeP The prime <code>p</code> defining the prime field.
+		 */
+		public X9FieldID(
+			BigInteger primeP)
+		{
+			this.id = X9ObjectIdentifiers.PrimeField;
+			this.parameters = new DerInteger(primeP);
+		}
+
+		/**
+		 * Constructor for elliptic curves over binary fields
+		 * <code>F<sub>2<sup>m</sup></sub></code>.
+		 * @param m  The exponent <code>m</code> of
+		 * <code>F<sub>2<sup>m</sup></sub></code>.
+		 * @param k1 The integer <code>k1</code> where <code>x<sup>m</sup> +
+		 * x<sup>k3</sup> + x<sup>k2</sup> + x<sup>k1</sup> + 1</code>
+		 * represents the reduction polynomial <code>f(z)</code>.
+		 * @param k2 The integer <code>k2</code> where <code>x<sup>m</sup> +
+		 * x<sup>k3</sup> + x<sup>k2</sup> + x<sup>k1</sup> + 1</code>
+		 * represents the reduction polynomial <code>f(z)</code>.
+		 * @param k3 The integer <code>k3</code> where <code>x<sup>m</sup> +
+		 * x<sup>k3</sup> + x<sup>k2</sup> + x<sup>k1</sup> + 1</code>
+		 * represents the reduction polynomial <code>f(z)</code>..
+		 */
+		public X9FieldID(
+			int m,
+			int k1,
+			int k2,
+			int k3)
+		{
+			this.id = X9ObjectIdentifiers.CharacteristicTwoField;
+
+			Asn1EncodableVector fieldIdParams = new Asn1EncodableVector(new DerInteger(m));
+
+			if (k2 == 0)
+			{
+				fieldIdParams.Add(
+					X9ObjectIdentifiers.TPBasis,
+					new DerInteger(k1));
+			}
+			else
+			{
+				fieldIdParams.Add(
+					X9ObjectIdentifiers.PPBasis,
+					new DerSequence(
+						new DerInteger(k1),
+						new DerInteger(k2),
+						new DerInteger(k3)));
+			}
+
+			this.parameters = new DerSequence(fieldIdParams);
+		}
+
+		internal X9FieldID(
+			Asn1Sequence seq)
+		{
+			this.id = (DerObjectIdentifier) seq[0];
+			this.parameters = (Asn1Object) seq[1];
+		}
+
+		public DerObjectIdentifier Identifier
+        {
+            get { return id; }
+        }
+
+		public Asn1Object Parameters
+        {
+            get { return parameters; }
+        }
+
+		/**
+         * Produce a Der encoding of the following structure.
+         * <pre>
+         *  FieldID ::= Sequence {
+         *      fieldType       FIELD-ID.&amp;id({IOSet}),
+         *      parameters      FIELD-ID.&amp;Type({IOSet}{&#64;fieldType})
+         *  }
+         * </pre>
+         */
+        public override Asn1Object ToAsn1Object()
+        {
+			return new DerSequence(id, parameters);
+        }
+    }
+}