src/java.base/share/classes/sun/security/ec/ECKeyPairGenerator.java

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package sun.security.ec;

import java.security.*;
import java.security.spec.AlgorithmParameterSpec;
import java.security.spec.ECGenParameterSpec;
import java.security.spec.ECParameterSpec;
import java.security.spec.InvalidParameterSpecException;
import java.util.Arrays;
import java.util.Optional;

import sun.security.jca.JCAUtil;
import sun.security.util.ECUtil;
import sun.security.util.math.*;

import static sun.security.util.SecurityProviderConstants.DEF_EC_KEY_SIZE;
import static sun.security.ec.ECOperations.IntermediateValueException;

/**
 * EC keypair generator.
 * Standard algorithm, minimum key length is 112 bits, maximum is 571 bits.
 *
 * @since 1.7
 */
public final class ECKeyPairGenerator extends KeyPairGeneratorSpi {

    private static final int KEY_SIZE_MIN = 112; // min bits (see ecc_impl.h)
    private static final int KEY_SIZE_MAX = 571; // max bits (see ecc_impl.h)

    // used to seed the keypair generator
    private SecureRandom random;

    // size of the key to generate, KEY_SIZE_MIN <= keySize <= KEY_SIZE_MAX
    private int keySize;

    // parameters specified via init, if any
    private AlgorithmParameterSpec params = null;

    /**
     * Constructs a new ECKeyPairGenerator.
     */
    public ECKeyPairGenerator() {
        // initialize to default in case the app does not call initialize()
        initialize(DEF_EC_KEY_SIZE, null);
    }

    // initialize the generator. See JCA doc
    @Override
    public void initialize(int keySize, SecureRandom random) {

        checkKeySize(keySize);
        this.params = ECUtil.getECParameterSpec(keySize);
        if (params == null) {
            throw new InvalidParameterException(
                "No EC parameters available for key size " + keySize + " bits");
        }
        this.random = random;
    }

    // second initialize method. See JCA doc
    @Override
    public void initialize(AlgorithmParameterSpec params, SecureRandom random)
            throws InvalidAlgorithmParameterException {

        ECParameterSpec ecSpec = null;

        if (params instanceof ECParameterSpec) {
            ECParameterSpec ecParams = (ECParameterSpec) params;
            ecSpec = ECUtil.getECParameterSpec(ecParams);
            if (ecSpec == null) {
                throw new InvalidAlgorithmParameterException(
                    "Curve not supported: " + params);
            }
        } else if (params instanceof ECGenParameterSpec) {
            String name = ((ECGenParameterSpec) params).getName();
            ecSpec = ECUtil.getECParameterSpec(name);
            if (ecSpec == null) {
                throw new InvalidAlgorithmParameterException(
                    "Unknown curve name: " + name);
            }
        } else {
            throw new InvalidAlgorithmParameterException(
                "ECParameterSpec or ECGenParameterSpec required for EC");
        }

        // Not all known curves are supported by the native implementation
        ensureCurveIsSupported(ecSpec);
        this.params = ecSpec;

        this.keySize = ecSpec.getCurve().getField().getFieldSize();
        this.random = random;
    }

    private static void ensureCurveIsSupported(ECParameterSpec ecSpec)
        throws InvalidAlgorithmParameterException {

        // Check if ecSpec is a valid curve
        AlgorithmParameters ecParams = ECUtil.getECParameters();
        try {
            ecParams.init(ecSpec);
        } catch (InvalidParameterSpecException ex) {
            throw new InvalidAlgorithmParameterException(
                "Curve not supported: " + ecSpec.toString());
        }

        // Check if the java implementation supports this curve
        if (ECOperations.forParameters(ecSpec).isEmpty()) {
            throw new InvalidAlgorithmParameterException(
                "Curve not supported: " + ecSpec.toString());
        }
    }

    // generate the keypair. See JCA doc
    @Override
    public KeyPair generateKeyPair() {

        if (random == null) {
            random = JCAUtil.getSecureRandom();
        }

        try {
            Optional<KeyPair> kp = generateKeyPairImpl(random);
            if (kp.isPresent()) {
                return kp.get();
            }
        } catch (Exception ex) {
            throw new ProviderException(ex);
        }
        throw new ProviderException("Curve not supported:  " +
            params.toString());
    }

    private byte[] generatePrivateScalar(SecureRandom random,
        ECOperations ecOps, int seedSize) {
        // Attempt to create the private scalar in a loop that uses new random
        // input each time. The chance of failure is very small assuming the
        // implementation derives the nonce using extra bits
        int numAttempts = 128;
        byte[] seedArr = new byte[seedSize];
        for (int i = 0; i < numAttempts; i++) {
            random.nextBytes(seedArr);
            try {
                return ecOps.seedToScalar(seedArr);
            } catch (IntermediateValueException ex) {
                // try again in the next iteration
            }
        }

        throw new ProviderException("Unable to produce private key after "
                                         + numAttempts + " attempts");
    }

    private Optional<KeyPair> generateKeyPairImpl(SecureRandom random)
        throws InvalidKeyException {

        ECParameterSpec ecParams = (ECParameterSpec) params;

        Optional<ECOperations> opsOpt = ECOperations.forParameters(ecParams);
        if (opsOpt.isEmpty()) {
            return Optional.empty();
        }
        ECOperations ops = opsOpt.get();
        IntegerFieldModuloP field = ops.getField();
        int numBits = ecParams.getOrder().bitLength();
        int seedBits = numBits + 64;
        int seedSize = (seedBits + 7) / 8;
        byte[] privArr = generatePrivateScalar(random, ops, seedSize);

        ECPrivateKeyImpl privateKey = new ECPrivateKeyImpl(privArr, ecParams);
        Arrays.fill(privArr, (byte)0);

        PublicKey publicKey = privateKey.calculatePublicKey();

        return Optional.of(new KeyPair(publicKey, privateKey));
    }

    private void checkKeySize(int keySize) throws InvalidParameterException {
        if (keySize < KEY_SIZE_MIN) {
            throw new InvalidParameterException
                ("Key size must be at least " + KEY_SIZE_MIN + " bits");
        }
        if (keySize > KEY_SIZE_MAX) {
            throw new InvalidParameterException
                ("Key size must be at most " + KEY_SIZE_MAX + " bits");
        }
        this.keySize = keySize;
    }
}