1 files changed, 114 insertions, 0 deletions
diff --git a/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/macs/GMac.java b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/macs/GMac.java
new file mode 100644
index 000000000..acaa819a4
--- /dev/null
+++ b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/macs/GMac.java
@@ -0,0 +1,114 @@
+package org.spongycastle.crypto.macs;
+
+import org.spongycastle.crypto.CipherParameters;
+import org.spongycastle.crypto.DataLengthException;
+import org.spongycastle.crypto.InvalidCipherTextException;
+import org.spongycastle.crypto.Mac;
+import org.spongycastle.crypto.modes.GCMBlockCipher;
+import org.spongycastle.crypto.params.AEADParameters;
+import org.spongycastle.crypto.params.KeyParameter;
+import org.spongycastle.crypto.params.ParametersWithIV;
+
+/**
+ * The GMAC specialisation of Galois/Counter mode (GCM) detailed in NIST Special Publication
+ * 800-38D.
+ * <p>
+ * GMac is an invocation of the GCM mode where no data is encrypted (i.e. all input data to the Mac
+ * is processed as additional authenticated data with the underlying GCM block cipher).
+ */
+public class GMac implements Mac
+{
+    private final GCMBlockCipher cipher;
+    private final int macSizeBits;
+
+    /**
+     * Creates a GMAC based on the operation of a block cipher in GCM mode.
+     * <p/>
+     * This will produce an authentication code the length of the block size of the cipher.
+     * 
+     * @param cipher
+     *            the cipher to be used in GCM mode to generate the MAC.
+     */
+    public GMac(final GCMBlockCipher cipher)
+    {
+        // use of this confused flow analyser in some earlier JDKs
+        this.cipher = cipher;
+        this.macSizeBits = 128;
+    }
+
+    /**
+     * Creates a GMAC based on the operation of a 128 bit block cipher in GCM mode.
+     * 
+     * @param macSizeBits
+     *            the mac size to generate, in bits. Must be a multiple of 8 and >= 96 and <= 128.
+     * @param cipher
+     *            the cipher to be used in GCM mode to generate the MAC.
+     */
+    public GMac(final GCMBlockCipher cipher, final int macSizeBits)
+    {
+        this.cipher = cipher;
+        this.macSizeBits = macSizeBits;
+    }
+
+    /**
+     * Initialises the GMAC - requires a {@link ParametersWithIV} providing a {@link KeyParameter}
+     * and a nonce.
+     */
+    public void init(final CipherParameters params) throws IllegalArgumentException
+    {
+        if (params instanceof ParametersWithIV)
+        {
+            final ParametersWithIV param = (ParametersWithIV)params;
+
+            final byte[] iv = param.getIV();
+            final KeyParameter keyParam = (KeyParameter)param.getParameters();
+
+            // GCM is always operated in encrypt mode to calculate MAC
+            cipher.init(true, new AEADParameters(keyParam, macSizeBits, iv));
+        }
+        else
+        {
+            throw new IllegalArgumentException("GMAC requires ParametersWithIV");
+        }
+    }
+
+    public String getAlgorithmName()
+    {
+        return cipher.getUnderlyingCipher().getAlgorithmName() + "-GMAC";
+    }
+
+    public int getMacSize()
+    {
+        return macSizeBits / 8;
+    }
+
+    public void update(byte in) throws IllegalStateException
+    {
+        cipher.processAADByte(in);
+    }
+
+    public void update(byte[] in, int inOff, int len)
+        throws DataLengthException, IllegalStateException
+    {
+        cipher.processAADBytes(in, inOff, len);
+    }
+
+    public int doFinal(byte[] out, int outOff)
+        throws DataLengthException, IllegalStateException
+    {
+        try
+        {
+            return cipher.doFinal(out, outOff);
+        }
+        catch (InvalidCipherTextException e)
+        {
+            // Impossible in encrypt mode
+            throw new IllegalStateException(e.toString());
+        }
+    }
+
+    public void reset()
+    {
+        cipher.reset();
+    }
+}