1 files changed, 148 insertions, 0 deletions
diff --git a/core/src/main/java/org/spongycastle/asn1/x9/X9FieldID.java b/core/src/main/java/org/spongycastle/asn1/x9/X9FieldID.java
new file mode 100644
index 00000000..831fc0b3
--- /dev/null
+++ b/core/src/main/java/org/spongycastle/asn1/x9/X9FieldID.java
@@ -0,0 +1,148 @@
+package org.spongycastle.asn1.x9;
+
+import java.math.BigInteger;
+
+import org.spongycastle.asn1.ASN1EncodableVector;
+import org.spongycastle.asn1.ASN1Integer;
+import org.spongycastle.asn1.ASN1Object;
+import org.spongycastle.asn1.ASN1ObjectIdentifier;
+import org.spongycastle.asn1.ASN1Primitive;
+import org.spongycastle.asn1.ASN1Sequence;
+import org.spongycastle.asn1.DERSequence;
+
+/**
+ * ASN.1 def for Elliptic-Curve Field ID structure. See
+ * X9.62, for further details.
+ */
+public class X9FieldID
+    extends ASN1Object
+    implements X9ObjectIdentifiers
+{
+    private ASN1ObjectIdentifier     id;
+    private ASN1Primitive 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 = prime_field;
+        this.parameters = new ASN1Integer(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>k1</sup> + 1</code>
+     * represents the reduction polynomial <code>f(z)</code>.
+     */
+    public X9FieldID(int m, int k1)
+    {
+        this(m, k1, 0, 0);
+    }
+
+    /**
+     * 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 = characteristic_two_field;
+        ASN1EncodableVector fieldIdParams = new ASN1EncodableVector();
+        fieldIdParams.add(new ASN1Integer(m));
+        
+        if (k2 == 0) 
+        {
+            if (k3 != 0)
+            {
+                throw new IllegalArgumentException("inconsistent k values");
+            }
+
+            fieldIdParams.add(tpBasis);
+            fieldIdParams.add(new ASN1Integer(k1));
+        } 
+        else 
+        {
+            if (k2 <= k1 || k3 <= k2)
+            {
+                throw new IllegalArgumentException("inconsistent k values");
+            }
+
+            fieldIdParams.add(ppBasis);
+            ASN1EncodableVector pentanomialParams = new ASN1EncodableVector();
+            pentanomialParams.add(new ASN1Integer(k1));
+            pentanomialParams.add(new ASN1Integer(k2));
+            pentanomialParams.add(new ASN1Integer(k3));
+            fieldIdParams.add(new DERSequence(pentanomialParams));
+        }
+        
+        this.parameters = new DERSequence(fieldIdParams);
+    }
+
+    private X9FieldID(
+        ASN1Sequence  seq)
+    {
+        this.id = ASN1ObjectIdentifier.getInstance(seq.getObjectAt(0));
+        this.parameters = seq.getObjectAt(1).toASN1Primitive();
+    }
+
+    public static X9FieldID getInstance(Object obj)
+    {
+        if (obj instanceof X9FieldID)
+        {
+            return (X9FieldID)obj;
+        }
+
+        if (obj != null)
+        {
+            return new X9FieldID(ASN1Sequence.getInstance(obj));
+        }
+
+        return null;
+    }
+
+    public ASN1ObjectIdentifier getIdentifier()
+    {
+        return id;
+    }
+
+    public ASN1Primitive getParameters()
+    {
+        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 ASN1Primitive toASN1Primitive()
+    {
+        ASN1EncodableVector v = new ASN1EncodableVector();
+
+        v.add(this.id);
+        v.add(this.parameters);
+
+        return new DERSequence(v);
+    }
+}