1 files changed, 126 insertions, 0 deletions
diff --git a/core/src/main/java/org/spongycastle/crypto/engines/RSABlindedEngine.java b/core/src/main/java/org/spongycastle/crypto/engines/RSABlindedEngine.java
new file mode 100644
index 00000000..d254f1c6
--- /dev/null
+++ b/core/src/main/java/org/spongycastle/crypto/engines/RSABlindedEngine.java
@@ -0,0 +1,126 @@
+package org.spongycastle.crypto.engines;
+
+import java.math.BigInteger;
+import java.security.SecureRandom;
+
+import org.spongycastle.crypto.AsymmetricBlockCipher;
+import org.spongycastle.crypto.CipherParameters;
+import org.spongycastle.crypto.DataLengthException;
+import org.spongycastle.crypto.params.ParametersWithRandom;
+import org.spongycastle.crypto.params.RSAKeyParameters;
+import org.spongycastle.crypto.params.RSAPrivateCrtKeyParameters;
+import org.spongycastle.util.BigIntegers;
+
+/**
+ * this does your basic RSA algorithm with blinding
+ */
+public class RSABlindedEngine
+    implements AsymmetricBlockCipher
+{
+    private static final BigInteger ONE = BigInteger.valueOf(1);
+
+    private RSACoreEngine    core = new RSACoreEngine();
+    private RSAKeyParameters key;
+    private SecureRandom     random;
+
+    /**
+     * initialise the RSA engine.
+     *
+     * @param forEncryption true if we are encrypting, false otherwise.
+     * @param param the necessary RSA key parameters.
+     */
+    public void init(
+        boolean             forEncryption,
+        CipherParameters    param)
+    {
+        core.init(forEncryption, param);
+
+        if (param instanceof ParametersWithRandom)
+        {
+            ParametersWithRandom    rParam = (ParametersWithRandom)param;
+
+            key = (RSAKeyParameters)rParam.getParameters();
+            random = rParam.getRandom();
+        }
+        else
+        {
+            key = (RSAKeyParameters)param;
+            random = new SecureRandom();
+        }
+    }
+
+    /**
+     * Return the maximum size for an input block to this engine.
+     * For RSA this is always one byte less than the key size on
+     * encryption, and the same length as the key size on decryption.
+     *
+     * @return maximum size for an input block.
+     */
+    public int getInputBlockSize()
+    {
+        return core.getInputBlockSize();
+    }
+
+    /**
+     * Return the maximum size for an output block to this engine.
+     * For RSA this is always one byte less than the key size on
+     * decryption, and the same length as the key size on encryption.
+     *
+     * @return maximum size for an output block.
+     */
+    public int getOutputBlockSize()
+    {
+        return core.getOutputBlockSize();
+    }
+
+    /**
+     * Process a single block using the basic RSA algorithm.
+     *
+     * @param in the input array.
+     * @param inOff the offset into the input buffer where the data starts.
+     * @param inLen the length of the data to be processed.
+     * @return the result of the RSA process.
+     * @exception DataLengthException the input block is too large.
+     */
+    public byte[] processBlock(
+        byte[]  in,
+        int     inOff,
+        int     inLen)
+    {
+        if (key == null)
+        {
+            throw new IllegalStateException("RSA engine not initialised");
+        }
+
+        BigInteger input = core.convertInput(in, inOff, inLen);
+
+        BigInteger result;
+        if (key instanceof RSAPrivateCrtKeyParameters)
+        {
+            RSAPrivateCrtKeyParameters k = (RSAPrivateCrtKeyParameters)key;
+
+            BigInteger e = k.getPublicExponent();
+            if (e != null)   // can't do blinding without a public exponent
+            {
+                BigInteger m = k.getModulus();
+                BigInteger r = BigIntegers.createRandomInRange(ONE, m.subtract(ONE), random);
+
+                BigInteger blindedInput = r.modPow(e, m).multiply(input).mod(m);
+                BigInteger blindedResult = core.processBlock(blindedInput);
+
+                BigInteger rInv = r.modInverse(m);
+                result = blindedResult.multiply(rInv).mod(m);
+            }
+            else
+            {
+                result = core.processBlock(input);
+            }
+        }
+        else
+        {
+            result = core.processBlock(input);
+        }
+
+        return core.convertOutput(result);
+    }
+}