1 files changed, 163 insertions, 0 deletions
diff --git a/core/src/main/java/org/spongycastle/crypto/signers/DSADigestSigner.java b/core/src/main/java/org/spongycastle/crypto/signers/DSADigestSigner.java
new file mode 100644
index 00000000..243752e5
--- /dev/null
+++ b/core/src/main/java/org/spongycastle/crypto/signers/DSADigestSigner.java
@@ -0,0 +1,163 @@
+package org.spongycastle.crypto.signers;
+
+import java.io.IOException;
+import java.math.BigInteger;
+
+import org.spongycastle.asn1.ASN1EncodableVector;
+import org.spongycastle.asn1.ASN1Encoding;
+import org.spongycastle.asn1.ASN1Integer;
+import org.spongycastle.asn1.ASN1Primitive;
+import org.spongycastle.asn1.ASN1Sequence;
+import org.spongycastle.asn1.DERSequence;
+import org.spongycastle.crypto.CipherParameters;
+import org.spongycastle.crypto.DSA;
+import org.spongycastle.crypto.Digest;
+import org.spongycastle.crypto.Signer;
+import org.spongycastle.crypto.params.AsymmetricKeyParameter;
+import org.spongycastle.crypto.params.ParametersWithRandom;
+
+public class DSADigestSigner
+    implements Signer
+{
+    private final Digest digest;
+    private final DSA dsaSigner;
+    private boolean forSigning;
+
+    public DSADigestSigner(
+        DSA    signer,
+        Digest digest)
+    {
+        this.digest = digest;
+        this.dsaSigner = signer;
+    }
+
+    public void init(
+        boolean           forSigning,
+        CipherParameters   parameters)
+    {
+        this.forSigning = forSigning;
+
+        AsymmetricKeyParameter k;
+
+        if (parameters instanceof ParametersWithRandom)
+        {
+            k = (AsymmetricKeyParameter)((ParametersWithRandom)parameters).getParameters();
+        }
+        else
+        {
+            k = (AsymmetricKeyParameter)parameters;
+        }
+
+        if (forSigning && !k.isPrivate())
+        {
+            throw new IllegalArgumentException("Signing Requires Private Key.");
+        }
+
+        if (!forSigning && k.isPrivate())
+        {
+            throw new IllegalArgumentException("Verification Requires Public Key.");
+        }
+
+        reset();
+
+        dsaSigner.init(forSigning, parameters);
+    }
+
+    /**
+     * update the internal digest with the byte b
+     */
+    public void update(
+        byte input)
+    {
+        digest.update(input);
+    }
+
+    /**
+     * update the internal digest with the byte array in
+     */
+    public void update(
+        byte[]  input,
+        int     inOff,
+        int     length)
+    {
+        digest.update(input, inOff, length);
+    }
+
+    /**
+     * Generate a signature for the message we've been loaded with using
+     * the key we were initialised with.
+     */
+    public byte[] generateSignature()
+    {
+        if (!forSigning)
+        {
+            throw new IllegalStateException("DSADigestSigner not initialised for signature generation.");
+        }
+
+        byte[] hash = new byte[digest.getDigestSize()];
+        digest.doFinal(hash, 0);
+
+        BigInteger[] sig = dsaSigner.generateSignature(hash);
+
+        try
+        {
+            return derEncode(sig[0], sig[1]);
+        }
+        catch (IOException e)
+        {
+            throw new IllegalStateException("unable to encode signature");
+        }
+    }
+
+    public boolean verifySignature(
+        byte[] signature)
+    {
+        if (forSigning)
+        {
+            throw new IllegalStateException("DSADigestSigner not initialised for verification");
+        }
+
+        byte[] hash = new byte[digest.getDigestSize()];
+        digest.doFinal(hash, 0);
+
+        try
+        {
+            BigInteger[] sig = derDecode(signature);
+            return dsaSigner.verifySignature(hash, sig[0], sig[1]);
+        }
+        catch (IOException e)
+        {
+            return false;
+        }
+    }
+
+    public void reset()
+    {
+        digest.reset();
+    }
+
+    private byte[] derEncode(
+        BigInteger  r,
+        BigInteger  s)
+        throws IOException
+    {
+        ASN1EncodableVector v = new ASN1EncodableVector();
+        v.add(new ASN1Integer(r));
+        v.add(new ASN1Integer(s));
+
+        return new DERSequence(v).getEncoded(ASN1Encoding.DER);
+    }
+
+    private BigInteger[] derDecode(
+        byte[] encoding)
+        throws IOException
+    {
+        ASN1Sequence s = (ASN1Sequence)ASN1Primitive.fromByteArray(encoding);
+
+        return new BigInteger[]
+        {
+            ((ASN1Integer)s.getObjectAt(0)).getValue(),
+            ((ASN1Integer)s.getObjectAt(1)).getValue()
+        };
+    }
+}