1 files changed, 169 insertions, 0 deletions
diff --git a/core/src/main/java/org/bouncycastle/crypto/signers/ECDSASigner.java b/core/src/main/java/org/bouncycastle/crypto/signers/ECDSASigner.java
new file mode 100644
index 00000000..a80c574b
--- /dev/null
+++ b/core/src/main/java/org/bouncycastle/crypto/signers/ECDSASigner.java
@@ -0,0 +1,169 @@
+package org.bouncycastle.crypto.signers;
+
+import java.math.BigInteger;
+import java.security.SecureRandom;
+
+import org.bouncycastle.crypto.CipherParameters;
+import org.bouncycastle.crypto.DSA;
+import org.bouncycastle.crypto.params.ECKeyParameters;
+import org.bouncycastle.crypto.params.ECPrivateKeyParameters;
+import org.bouncycastle.crypto.params.ECPublicKeyParameters;
+import org.bouncycastle.crypto.params.ParametersWithRandom;
+import org.bouncycastle.math.ec.ECAlgorithms;
+import org.bouncycastle.math.ec.ECConstants;
+import org.bouncycastle.math.ec.ECPoint;
+
+/**
+ * EC-DSA as described in X9.62
+ */
+public class ECDSASigner
+    implements ECConstants, DSA
+{
+    ECKeyParameters key;
+
+    SecureRandom    random;
+
+    public void init(
+        boolean                 forSigning,
+        CipherParameters        param)
+    {
+        if (forSigning)
+        {
+            if (param instanceof ParametersWithRandom)
+            {
+                ParametersWithRandom    rParam = (ParametersWithRandom)param;
+
+                this.random = rParam.getRandom();
+                this.key = (ECPrivateKeyParameters)rParam.getParameters();
+            }
+            else
+            {
+                this.random = new SecureRandom();
+                this.key = (ECPrivateKeyParameters)param;
+            }
+        }
+        else
+        {
+            this.key = (ECPublicKeyParameters)param;
+        }
+    }
+
+    // 5.3 pg 28
+    /**
+     * generate a signature for the given message using the key we were
+     * initialised with. For conventional DSA the message should be a SHA-1
+     * hash of the message of interest.
+     *
+     * @param message the message that will be verified later.
+     */
+    public BigInteger[] generateSignature(
+        byte[] message)
+    {
+        BigInteger n = key.getParameters().getN();
+        BigInteger e = calculateE(n, message);
+        BigInteger r = null;
+        BigInteger s = null;
+
+        // 5.3.2
+        do // generate s
+        {
+            BigInteger k = null;
+            int        nBitLength = n.bitLength();
+
+            do // generate r
+            {
+                do
+                {
+                    k = new BigInteger(nBitLength, random);
+                }
+                while (k.equals(ZERO) || k.compareTo(n) >= 0);
+
+                ECPoint p = key.getParameters().getG().multiply(k);
+
+                // 5.3.3
+                BigInteger x = p.getX().toBigInteger();
+
+                r = x.mod(n);
+            }
+            while (r.equals(ZERO));
+
+            BigInteger d = ((ECPrivateKeyParameters)key).getD();
+
+            s = k.modInverse(n).multiply(e.add(d.multiply(r))).mod(n);
+        }
+        while (s.equals(ZERO));
+
+        BigInteger[]  res = new BigInteger[2];
+
+        res[0] = r;
+        res[1] = s;
+
+        return res;
+    }
+
+    // 5.4 pg 29
+    /**
+     * return true if the value r and s represent a DSA signature for
+     * the passed in message (for standard DSA the message should be
+     * a SHA-1 hash of the real message to be verified).
+     */
+    public boolean verifySignature(
+        byte[]      message,
+        BigInteger  r,
+        BigInteger  s)
+    {
+        BigInteger n = key.getParameters().getN();
+        BigInteger e = calculateE(n, message);
+
+        // r in the range [1,n-1]
+        if (r.compareTo(ONE) < 0 || r.compareTo(n) >= 0)
+        {
+            return false;
+        }
+
+        // s in the range [1,n-1]
+        if (s.compareTo(ONE) < 0 || s.compareTo(n) >= 0)
+        {
+            return false;
+        }
+
+        BigInteger c = s.modInverse(n);
+
+        BigInteger u1 = e.multiply(c).mod(n);
+        BigInteger u2 = r.multiply(c).mod(n);
+
+        ECPoint G = key.getParameters().getG();
+        ECPoint Q = ((ECPublicKeyParameters)key).getQ();
+
+        ECPoint point = ECAlgorithms.sumOfTwoMultiplies(G, u1, Q, u2);
+
+        // components must be bogus.
+        if (point.isInfinity())
+        {
+            return false;
+        }
+
+        BigInteger v = point.getX().toBigInteger().mod(n);
+
+        return v.equals(r);
+    }
+
+    private BigInteger calculateE(BigInteger n, byte[] message)
+    {
+        int log2n = n.bitLength();
+        int messageBitLength = message.length * 8;
+
+        if (log2n >= messageBitLength)
+        {
+            return new BigInteger(1, message);
+        }
+        else
+        {
+            BigInteger trunc = new BigInteger(1, message);
+
+            trunc = trunc.shiftRight(messageBitLength - log2n);
+
+            return trunc;
+        }
+    }
+}