1 files changed, 164 insertions, 0 deletions
diff --git a/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/kems/RSAKeyEncapsulation.java b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/kems/RSAKeyEncapsulation.java
new file mode 100755
index 000000000..5f9a7f519
--- /dev/null
+++ b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/kems/RSAKeyEncapsulation.java
@@ -0,0 +1,164 @@
+package org.spongycastle.crypto.kems;
+
+import java.math.BigInteger;
+import java.security.SecureRandom;
+
+import org.spongycastle.crypto.CipherParameters;
+import org.spongycastle.crypto.DerivationFunction;
+import org.spongycastle.crypto.KeyEncapsulation;
+import org.spongycastle.crypto.params.KDFParameters;
+import org.spongycastle.crypto.params.KeyParameter;
+import org.spongycastle.crypto.params.RSAKeyParameters;
+import org.spongycastle.util.BigIntegers;
+
+/**
+ * The RSA Key Encapsulation Mechanism (RSA-KEM) from ISO 18033-2.
+ */
+public class RSAKeyEncapsulation
+    implements KeyEncapsulation
+{
+    private static final BigInteger ZERO = BigInteger.valueOf(0);
+    private static final BigInteger ONE = BigInteger.valueOf(1);
+
+    private DerivationFunction kdf;
+    private SecureRandom rnd;
+    private RSAKeyParameters key;
+
+    /**
+     * Set up the RSA-KEM.
+     *
+     * @param kdf the key derivation function to be used.
+     * @param rnd the random source for the session key.
+     */
+    public RSAKeyEncapsulation(
+        DerivationFunction kdf,
+        SecureRandom rnd)
+    {
+        this.kdf = kdf;
+        this.rnd = rnd;
+    }
+
+
+    /**
+     * Initialise the RSA-KEM.
+     *
+     * @param key the recipient's public (for encryption) or private (for decryption) key.
+     */
+    public void init(CipherParameters key)
+        throws IllegalArgumentException
+    {
+        if (!(key instanceof RSAKeyParameters))
+        {
+            throw new IllegalArgumentException("RSA key required");
+        }
+        else
+        {
+            this.key = (RSAKeyParameters)key;
+        }
+    }
+
+
+    /**
+     * Generate and encapsulate a random session key.
+     *
+     * @param out    the output buffer for the encapsulated key.
+     * @param outOff the offset for the output buffer.
+     * @param keyLen the length of the random session key.
+     * @return the random session key.
+     */
+    public CipherParameters encrypt(byte[] out, int outOff, int keyLen)
+        throws IllegalArgumentException
+    {
+        if (key.isPrivate())
+        {
+            throw new IllegalArgumentException("Public key required for encryption");
+        }
+
+        BigInteger n = key.getModulus();
+        BigInteger e = key.getExponent();
+
+        // Generate the ephemeral random and encode it    
+        BigInteger r = BigIntegers.createRandomInRange(ZERO, n.subtract(ONE), rnd);
+        byte[] R = BigIntegers.asUnsignedByteArray((n.bitLength() + 7) / 8, r);
+
+        // Encrypt the random and encode it     
+        BigInteger c = r.modPow(e, n);
+        byte[] C = BigIntegers.asUnsignedByteArray((n.bitLength() + 7) / 8, c);
+        System.arraycopy(C, 0, out, outOff, C.length);
+
+
+        // Initialise the KDF
+        kdf.init(new KDFParameters(R, null));
+
+        // Generate the secret key
+        byte[] K = new byte[keyLen];
+        kdf.generateBytes(K, 0, K.length);
+
+        return new KeyParameter(K);
+    }
+
+
+    /**
+     * Generate and encapsulate a random session key.
+     *
+     * @param out    the output buffer for the encapsulated key.
+     * @param keyLen the length of the random session key.
+     * @return the random session key.
+     */
+    public CipherParameters encrypt(byte[] out, int keyLen)
+    {
+        return encrypt(out, 0, keyLen);
+    }
+
+
+    /**
+     * Decrypt an encapsulated session key.
+     *
+     * @param in     the input buffer for the encapsulated key.
+     * @param inOff  the offset for the input buffer.
+     * @param inLen  the length of the encapsulated key.
+     * @param keyLen the length of the session key.
+     * @return the session key.
+     */
+    public CipherParameters decrypt(byte[] in, int inOff, int inLen, int keyLen)
+        throws IllegalArgumentException
+    {
+        if (!key.isPrivate())
+        {
+            throw new IllegalArgumentException("Private key required for decryption");
+        }
+
+        BigInteger n = key.getModulus();
+        BigInteger d = key.getExponent();
+
+        // Decode the input
+        byte[] C = new byte[inLen];
+        System.arraycopy(in, inOff, C, 0, C.length);
+        BigInteger c = new BigInteger(1, C);
+
+        // Decrypt the ephemeral random and encode it
+        BigInteger r = c.modPow(d, n);
+        byte[] R = BigIntegers.asUnsignedByteArray((n.bitLength() + 7) / 8, r);
+
+        // Initialise the KDF
+        kdf.init(new KDFParameters(R, null));
+
+        // Generate the secret key
+        byte[] K = new byte[keyLen];
+        kdf.generateBytes(K, 0, K.length);
+
+        return new KeyParameter(K);
+    }
+
+    /**
+     * Decrypt an encapsulated session key.
+     *
+     * @param in     the input buffer for the encapsulated key.
+     * @param keyLen the length of the session key.
+     * @return the session key.
+     */
+    public CipherParameters decrypt(byte[] in, int keyLen)
+    {
+        return decrypt(in, 0, in.length, keyLen);
+    }
+}