1 files changed, 179 insertions, 0 deletions
diff --git a/src/org/bouncycastle/math/ec/ECCurve.java b/src/org/bouncycastle/math/ec/ECCurve.java
new file mode 100644
index 0000000..ee7ddc3
--- /dev/null
+++ b/src/org/bouncycastle/math/ec/ECCurve.java
@@ -0,0 +1,179 @@
+package org.bouncycastle.math.ec;
+
+import java.math.BigInteger;
+
+/**
+ * base class for an elliptic curve
+ */
+public abstract class ECCurve
+{
+    ECFieldElement a, b;
+
+    public abstract int getFieldSize();
+
+    public abstract ECFieldElement fromBigInteger(BigInteger x);
+
+    public abstract ECPoint createPoint(BigInteger x, BigInteger y, boolean withCompression);
+
+    public abstract ECPoint decodePoint(byte[] encoded);
+
+    public abstract ECPoint getInfinity();
+
+    public ECFieldElement getA()
+    {
+        return a;
+    }
+
+    public ECFieldElement getB()
+    {
+        return b;
+    }
+
+    /**
+     * Elliptic curve over Fp
+     */
+    public static class Fp extends ECCurve
+    {
+        BigInteger q;
+        ECPoint.Fp infinity;
+
+        public Fp(BigInteger q, BigInteger a, BigInteger b)
+        {
+            this.q = q;
+            this.a = fromBigInteger(a);
+            this.b = fromBigInteger(b);
+            this.infinity = new ECPoint.Fp(this, null, null);
+        }
+
+        public BigInteger getQ()
+        {
+            return q;
+        }
+
+        @Override
+        public int getFieldSize()
+        {
+            return q.bitLength();
+        }
+
+        @Override
+        public ECFieldElement fromBigInteger(BigInteger x)
+        {
+            return new ECFieldElement.Fp(this.q, x);
+        }
+
+        @Override
+        public ECPoint createPoint(BigInteger x, BigInteger y, boolean withCompression)
+        {
+            return new ECPoint.Fp(this, fromBigInteger(x), fromBigInteger(y), withCompression);
+        }
+
+        /**
+         * Decode a point on this curve from its ASN.1 encoding. The different
+         * encodings are taken account of, including point compression for
+         * <code>F<sub>p</sub></code> (X9.62 s 4.2.1 pg 17).
+         * @return The decoded point.
+         */
+        @Override
+        public ECPoint decodePoint(byte[] encoded)
+        {
+            ECPoint p = null;
+
+            switch (encoded[0])
+            {
+                // infinity
+            case 0x00:
+                if (encoded.length > 1)
+                {
+                    throw new RuntimeException("Invalid point encoding");
+                }
+                p = getInfinity();
+                break;
+                // compressed
+            case 0x02:
+            case 0x03:
+                int ytilde = encoded[0] & 1;
+                byte[]  i = new byte[encoded.length - 1];
+
+                System.arraycopy(encoded, 1, i, 0, i.length);
+
+                ECFieldElement x = new ECFieldElement.Fp(this.q, new BigInteger(1, i));
+                ECFieldElement alpha = x.multiply(x.square().add(a)).add(b);
+                ECFieldElement beta = alpha.sqrt();
+
+                //
+                // if we can't find a sqrt we haven't got a point on the
+                // curve - run!
+                //
+                if (beta == null)
+                {
+                    throw new RuntimeException("Invalid point compression");
+                }
+
+                int bit0 = (beta.toBigInteger().testBit(0) ? 1 : 0);
+
+                if (bit0 == ytilde)
+                {
+                    p = new ECPoint.Fp(this, x, beta, true);
+                }
+                else
+                {
+                    p = new ECPoint.Fp(this, x,
+                        new ECFieldElement.Fp(this.q, q.subtract(beta.toBigInteger())), true);
+                }
+                break;
+                // uncompressed
+            case 0x04:
+                // hybrid
+            case 0x06:
+            case 0x07:
+                byte[]  xEnc = new byte[(encoded.length - 1) / 2];
+                byte[]  yEnc = new byte[(encoded.length - 1) / 2];
+
+                System.arraycopy(encoded, 1, xEnc, 0, xEnc.length);
+                System.arraycopy(encoded, xEnc.length + 1, yEnc, 0, yEnc.length);
+
+                p = new ECPoint.Fp(this,
+                        new ECFieldElement.Fp(this.q, new BigInteger(1, xEnc)),
+                        new ECFieldElement.Fp(this.q, new BigInteger(1, yEnc)));
+                break;
+            default:
+                throw new RuntimeException("Invalid point encoding 0x" + Integer.toString(encoded[0], 16));
+            }
+
+            return p;
+        }
+
+        @Override
+        public ECPoint getInfinity()
+        {
+            return infinity;
+        }
+
+        @Override
+        public boolean equals(
+            Object anObject)
+        {
+            if (anObject == this)
+            {
+                return true;
+            }
+
+            if (!(anObject instanceof ECCurve.Fp))
+            {
+                return false;
+            }
+
+            ECCurve.Fp other = (ECCurve.Fp) anObject;
+
+            return this.q.equals(other.q)
+                    && a.equals(other.a) && b.equals(other.b);
+        }
+
+        @Override
+        public int hashCode()
+        {
+            return a.hashCode() ^ b.hashCode() ^ q.hashCode();
+        }
+    }
+}