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

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package sun.security.ec;

import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.math.BigInteger;

import java.security.*;
import java.security.interfaces.*;
import java.security.spec.*;
import java.util.Arrays;

import sun.security.ec.point.AffinePoint;
import sun.security.ec.point.MutablePoint;
import sun.security.util.*;
import sun.security.x509.AlgorithmId;
import sun.security.pkcs.PKCS8Key;
import sun.security.x509.X509Key;

/**
 * Key implementation for EC private keys.
 * <p>
 * ASN.1 syntax for EC private keys from SEC 1 v1.5 (draft):
 *
 * <pre>
 * EXPLICIT TAGS
 *
 * ECPrivateKey ::= SEQUENCE {
 *   version INTEGER { ecPrivkeyVer1(1) } (ecPrivkeyVer1),
 *   privateKey OCTET STRING,
 *   parameters [0] ECDomainParameters {{ SECGCurveNames }} OPTIONAL,
 *   publicKey [1] BIT STRING OPTIONAL
 * }
 * </pre>
 *
 * We currently ignore the optional parameters and publicKey fields. We
 * require that the parameters are encoded as part of the AlgorithmIdentifier,
 * not in the private key structure.
 *
 * @since   1.6
 * @author  Andreas Sterbenz
 */
public final class ECPrivateKeyImpl extends PKCS8Key implements ECPrivateKey {

    @java.io.Serial
    private static final long serialVersionUID = 88695385615075129L;

    private BigInteger s;       // private value
    private byte[] arrayS;      // private value as a little-endian array
    @SuppressWarnings("serial") // Type of field is not Serializable
    private ECParameterSpec params;
    private byte[] domainParams;  //Currently unsupported

    /**
     * Construct a key from its encoding. Called by the ECKeyFactory.
     */
    ECPrivateKeyImpl(byte[] encoded) throws InvalidKeyException {
        super(encoded);
        parseKeyBits();
    }

    /**
     * Construct a key from its components. Used by the
     * KeyFactory.
     */
    ECPrivateKeyImpl(BigInteger s, ECParameterSpec params)
            throws InvalidKeyException {
        this.s = s;
        this.params = params;
        makeEncoding(s);

    }

    ECPrivateKeyImpl(byte[] s, ECParameterSpec params)
            throws InvalidKeyException {
        this.arrayS = s.clone();
        this.params = params;
        makeEncoding(s);
    }

    private void makeEncoding(byte[] s) throws InvalidKeyException {
        algid = new AlgorithmId
                (AlgorithmId.EC_oid, ECParameters.getAlgorithmParameters(params));
        DerOutputStream out = new DerOutputStream();
        out.putInteger(1); // version 1
        byte[] privBytes = s.clone();
        ArrayUtil.reverse(privBytes);
        out.putOctetString(privBytes);
        Arrays.fill(privBytes, (byte) 0);
        DerValue val = DerValue.wrap(DerValue.tag_Sequence, out);
        privKeyMaterial = val.toByteArray();
        val.clear();
    }

    private void makeEncoding(BigInteger s) throws InvalidKeyException {
        algid = new AlgorithmId(AlgorithmId.EC_oid,
                ECParameters.getAlgorithmParameters(params));
        byte[] sArr = s.toByteArray();
        // convert to fixed-length array
        int numOctets = (params.getOrder().bitLength() + 7) / 8;
        byte[] sOctets = new byte[numOctets];
        int inPos = Math.max(sArr.length - sOctets.length, 0);
        int outPos = Math.max(sOctets.length - sArr.length, 0);
        int length = Math.min(sArr.length, sOctets.length);
        System.arraycopy(sArr, inPos, sOctets, outPos, length);
        Arrays.fill(sArr, (byte) 0);

        DerOutputStream out = new DerOutputStream();
        out.putInteger(1); // version 1
        out.putOctetString(sOctets);
        Arrays.fill(sOctets, (byte) 0);
        DerValue val = DerValue.wrap(DerValue.tag_Sequence, out);
        privKeyMaterial = val.toByteArray();
        val.clear();
    }

    // see JCA doc
    public String getAlgorithm() {
        return "EC";
    }

    // see JCA doc
    public BigInteger getS() {
        if (s == null) {
            byte[] arrCopy = arrayS.clone();
            ArrayUtil.reverse(arrCopy);
            s = new BigInteger(1, arrCopy);
            Arrays.fill(arrCopy, (byte)0);
        }
        return s;
    }

    // Return the internal arrayS byte[], if arrayS is null generate it.
    public byte[] getArrayS() {
        if (arrayS == null) {
            arrayS = ECUtil.sArray(getS(), params);
        }
        return arrayS;
    }

    // see JCA doc
    public ECParameterSpec getParams() {
        return params;
    }

    /**
     * Parse the ASN.1 of the privateKey Octet
     */
    private void parseKeyBits() throws InvalidKeyException {
        // Parse private key material from PKCS8Key.decode()
        try {
            DerInputStream in = new DerInputStream(privKeyMaterial);
            DerValue derValue = in.getDerValue();
            if (derValue.tag != DerValue.tag_Sequence) {
                throw new IOException("Not a SEQUENCE");
            }
            DerInputStream data = derValue.data;
            int version = data.getInteger();
            if (version != V2) {
                throw new IOException("Version must be 1");
            }
            byte[] privData = data.getOctetString();
            ArrayUtil.reverse(privData);
            arrayS = privData;

            // Validate parameters stored from PKCS8Key.decode()
            AlgorithmParameters algParams = this.algid.getParameters();
            if (algParams == null) {
                throw new InvalidKeyException("EC domain parameters must be "
                    + "encoded in the algorithm identifier");
            }
            params = algParams.getParameterSpec(ECParameterSpec.class);

            if (data.available() == 0) {
                return;
            }

            DerValue value = data.getDerValue();
            if (value.isContextSpecific((byte) 0)) {
                domainParams = value.getDataBytes();  // Save DER sequence
                if (data.available() == 0) {
                    return;
                }
                value = data.getDerValue();
            }

            if (value.isContextSpecific((byte) 1)) {
                DerValue bits = value.withTag(DerValue.tag_BitString);
                pubKeyEncoded = new X509Key(algid,
                    bits.data.getUnalignedBitString()).getEncoded();
            } else {
                throw new InvalidKeyException("Unexpected value: " + value);
            }

        } catch (IOException | InvalidParameterSpecException e) {
            throw new InvalidKeyException("Invalid EC private key", e);
        }
    }

    public PublicKey calculatePublicKey() {
        ECParameterSpec ecParams = getParams();
        ECOperations ops = ECOperations.forParameters(ecParams)
                .orElseThrow(ProviderException::new);
        MutablePoint pub = ops.multiply(ecParams.getGenerator(), getArrayS());
        AffinePoint affPub = pub.asAffine();
        ECPoint w = new ECPoint(affPub.getX().asBigInteger(),
                affPub.getY().asBigInteger());
        try {
            return new ECPublicKeyImpl(w, ecParams);
        } catch (InvalidKeyException e) {
            throw new ProviderException(
                    "Unexpected error calculating public key", e);
        }
    }

    /**
     * Restores the state of this object from the stream.
     * <p>
     * Deserialization of this object is not supported.
     *
     * @param  stream the {@code ObjectInputStream} from which data is read
     * @throws IOException if an I/O error occurs
     * @throws ClassNotFoundException if a serialized class cannot be loaded
     */
    @java.io.Serial
    private void readObject(ObjectInputStream stream)
            throws IOException, ClassNotFoundException {
        throw new InvalidObjectException(
                "ECPrivateKeyImpl keys are not directly deserializable");
    }
}