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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 and up.
package org.bouncycastle.crypto.kems;
import java.math.BigInteger;
import java.security.SecureRandom;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.DerivationFunction;
import org.bouncycastle.crypto.KeyEncapsulation;
import org.bouncycastle.crypto.params.ECDomainParameters;
import org.bouncycastle.crypto.params.ECKeyParameters;
import org.bouncycastle.crypto.params.ECPrivateKeyParameters;
import org.bouncycastle.crypto.params.ECPublicKeyParameters;
import org.bouncycastle.crypto.params.KDFParameters;
import org.bouncycastle.crypto.params.KeyParameter;
import org.bouncycastle.math.ec.ECCurve;
import org.bouncycastle.math.ec.ECMultiplier;
import org.bouncycastle.math.ec.ECPoint;
import org.bouncycastle.math.ec.FixedPointCombMultiplier;
import org.bouncycastle.util.Arrays;
import org.bouncycastle.util.BigIntegers;
/**
* The ECIES Key Encapsulation Mechanism (ECIES-KEM) from ISO 18033-2.
*/
public class ECIESKeyEncapsulation
implements KeyEncapsulation
{
private static final BigInteger ONE = BigInteger.valueOf(1);
private DerivationFunction kdf;
private SecureRandom rnd;
private ECKeyParameters key;
private boolean CofactorMode;
private boolean OldCofactorMode;
private boolean SingleHashMode;
/**
* Set up the ECIES-KEM.
*
* @param kdf the key derivation function to be used.
* @param rnd the random source for the session key.
*/
public ECIESKeyEncapsulation(
DerivationFunction kdf,
SecureRandom rnd)
{
this.kdf = kdf;
this.rnd = rnd;
this.CofactorMode = false;
this.OldCofactorMode = false;
this.SingleHashMode = false;
}
/**
* Set up the ECIES-KEM.
*
* @param kdf the key derivation function to be used.
* @param rnd the random source for the session key.
* @param cofactorMode if true use the new cofactor ECDH.
* @param oldCofactorMode if true use the old cofactor ECDH.
* @param singleHashMode if true use single hash mode.
*/
public ECIESKeyEncapsulation(
DerivationFunction kdf,
SecureRandom rnd,
boolean cofactorMode,
boolean oldCofactorMode,
boolean singleHashMode)
{
this.kdf = kdf;
this.rnd = rnd;
// If both cofactorMode and oldCofactorMode are set to true
// then the implementation will use the new cofactor ECDH
this.CofactorMode = cofactorMode;
// https://www.shoup.net/iso/std4.pdf, Page 34.
if (cofactorMode)
{
this.OldCofactorMode = false;
}
else
{
this.OldCofactorMode = oldCofactorMode;
}
this.SingleHashMode = singleHashMode;
}
/**
* Initialise the ECIES-KEM.
*
* @param key the recipient's public (for encryption) or private (for decryption) key.
*/
public void init(CipherParameters key)
throws IllegalArgumentException
{
if (!(key instanceof ECKeyParameters))
{
throw new IllegalArgumentException("EC key required");
}
else
{
this.key = (ECKeyParameters)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 session key.
* @return the random session key.
*/
public CipherParameters encrypt(byte[] out, int outOff, int keyLen)
throws IllegalArgumentException
{
if (!(key instanceof ECPublicKeyParameters))
{
throw new IllegalArgumentException("Public key required for encryption");
}
ECPublicKeyParameters ecPubKey = (ECPublicKeyParameters)key;
ECDomainParameters ecParams = ecPubKey.getParameters();
ECCurve curve = ecParams.getCurve();
BigInteger n = ecParams.getN();
BigInteger h = ecParams.getH();
// Generate the ephemeral key pair
BigInteger r = BigIntegers.createRandomInRange(ONE, n, rnd);
// Compute the static-ephemeral key agreement
BigInteger rPrime = OldCofactorMode ? r.multiply(h).mod(n) : r;
ECMultiplier basePointMultiplier = createBasePointMultiplier();
ECPoint[] ghTilde = new ECPoint[]{
basePointMultiplier.multiply(ecParams.getG(), r),
ecPubKey.getQ().multiply(rPrime)
};
// NOTE: More efficient than normalizing each individually
curve.normalizeAll(ghTilde);
ECPoint gTilde = ghTilde[0], hTilde = ghTilde[1];
// Encode the ephemeral public key
byte[] C = gTilde.getEncoded(false);
System.arraycopy(C, 0, out, outOff, C.length);
// Encode the shared secret value
byte[] PEH = hTilde.getAffineXCoord().getEncoded();
return deriveKey(keyLen, C, PEH);
}
/**
* Generate and encapsulate a random session key.
*
* @param out the output buffer for the encapsulated key.
* @param keyLen the length of the 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 instanceof ECPrivateKeyParameters))
{
throw new IllegalArgumentException("Private key required for encryption");
}
ECPrivateKeyParameters ecPrivKey = (ECPrivateKeyParameters)key;
ECDomainParameters ecParams = ecPrivKey.getParameters();
ECCurve curve = ecParams.getCurve();
BigInteger n = ecParams.getN();
BigInteger h = ecParams.getH();
// Decode the ephemeral public key
byte[] C = new byte[inLen];
System.arraycopy(in, inOff, C, 0, inLen);
// NOTE: Decoded points are already normalized (i.e in affine form)
ECPoint gTilde = curve.decodePoint(C);
// Compute the static-ephemeral key agreement
ECPoint gHat = gTilde;
if ((CofactorMode) || (OldCofactorMode))
{
gHat = gHat.multiply(h);
}
BigInteger xHat = ecPrivKey.getD();
if (CofactorMode)
{
xHat = xHat.multiply(ecParams.getHInv()).mod(n);
}
ECPoint hTilde = gHat.multiply(xHat).normalize();
// Encode the shared secret value
byte[] PEH = hTilde.getAffineXCoord().getEncoded();
return deriveKey(keyLen, C, PEH);
}
/**
* 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);
}
protected ECMultiplier createBasePointMultiplier()
{
return new FixedPointCombMultiplier();
}
protected KeyParameter deriveKey(int keyLen, byte[] C, byte[] PEH)
{
byte[] kdfInput = PEH;
if (!SingleHashMode)
{
kdfInput = Arrays.concatenate(C, PEH);
Arrays.fill(PEH, (byte)0);
}
try
{
// Initialise the KDF
kdf.init(new KDFParameters(kdfInput, null));
// Generate the secret key
byte[] K = new byte[keyLen];
kdf.generateBytes(K, 0, K.length);
// Return the ciphertext
return new KeyParameter(K);
}
finally
{
Arrays.fill(kdfInput, (byte)0);
}
}
}