package com.nimbusds.jose.jwk;


import java.math.BigInteger;
import java.net.URL;
import java.util.List;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.NoSuchAlgorithmException;
import java.security.interfaces.ECPrivateKey;
import java.security.interfaces.ECPublicKey;
import java.security.spec.ECParameterSpec;
import java.security.spec.ECPoint;
import java.security.spec.ECPrivateKeySpec;
import java.security.spec.ECPublicKeySpec;
import java.security.spec.InvalidKeySpecException;
import java.text.ParseException;
import java.util.Set;

import net.jcip.annotations.Immutable;

import net.minidev.json.JSONObject;

import org.bouncycastle.jce.ECNamedCurveTable;
import org.bouncycastle.jce.spec.ECNamedCurveParameterSpec;
import org.bouncycastle.jce.spec.ECNamedCurveSpec;

import com.nimbusds.jose.Algorithm;
import com.nimbusds.jose.crypto.BouncyCastleProviderSingleton;
import com.nimbusds.jose.util.*;


/**
 * Public and private {@link KeyType#EC Elliptic Curve} JSON Web Key (JWK). 
 * Uses the BouncyCastle.org provider for EC key import and export. This class
 * is immutable.
 *
 * <p>Example JSON object representation of a public EC JWK:
 * 
 * <pre>
 * {
 *   "kty" : "EC",
 *   "crv" : "P-256",
 *   "x"   : "MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4",
 *   "y"   : "4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM",
 *   "use" : "enc",
 *   "kid" : "1"
 * }
 * </pre>
 *
 * <p>Example JSON object representation of a public and private EC JWK:
 *
 * <pre>
 * {
 *   "kty" : "EC",
 *   "crv" : "P-256",
 *   "x"   : "MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4",
 *   "y"   : "4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM",
 *   "d"   : "870MB6gfuTJ4HtUnUvYMyJpr5eUZNP4Bk43bVdj3eAE",
 *   "use" : "enc",
 *   "kid" : "1"
 * }
 * </pre>
 *
 * <p>See http://en.wikipedia.org/wiki/Elliptic_curve_cryptography
 *
 * @author Vladimir Dzhuvinov
 * @author Justin Richer
 * @version $version$ (2014-04-02)
 */
@Immutable
public final class ECKey extends JWK {


        /**
         * Cryptographic curve. This class is immutable.
         *
         * <p>Includes constants for the following standard cryptographic 
         * curves:
         *
         * <ul>
         *     <li>{@link #P_256}
         *     <li>{@link #P_384}
         *     <li>{@link #P_521}
         * </ul>
         *
         * <p>See "Digital Signature Standard (DSS)", FIPS PUB 186-3, June 
         * 2009, National Institute of Standards and Technology (NIST).
         */
        @Immutable
        public static class Curve {


                /**
                 * P-256 curve (secp256r1).
                 */
                public static final Curve P_256 = new Curve("P-256", "secp256r1");


                /**
                 * P-384 curve (secp384r1).
                 */
                public static final Curve P_384 = new Curve("P-384", "secp384r1");


                /**
                 * P-521 curve (secp521r1).
                 */
                public static final Curve P_521 = new Curve("P-521", "secp521r1");


                /**
                 * The JOSE curve name.
                 */
                private final String name;


                /**
                 * The standard (JCA) curve name, {@code null} if not 
                 * specified.
                 */
                private final String stdName;


                /**
                 * Creates a new cryptographic curve with the specified name.
                 * The standard (JCA) curve name is not unspecified.
                 *
                 * @param name The name of the cryptographic curve. Must not be
                 *             {@code null}.
                 */
                public Curve(final String name) {

                        this(name, null);
                }


                /**
                 * Creates a new cryptographic curve with the specified name.
                 *
                 * @param name    The JOSE name of the cryptographic curve. 
                 *                Must not be {@code null}.
                 * @param stdName The standard (JCA) name of the cryptographic
                 *                curve, {@code null} if not specified.
                 */
                public Curve(final String name, final String stdName) {

                        if (name == null) {
                                throw new IllegalArgumentException("The cryptographic curve name must not be null");
                        }

                        this.name = name;

                        this.stdName = stdName;
                }


                /**
                 * Gets the name of this cryptographic curve.
                 *
                 * @return The name.
                 */
                public String getName() {

                        return name;
                }


                /**
                 * Gets the standard (JCA) name of this cryptographic curve.
                 *
                 * @return The standard (JCA) name.
                 */
                public String getStdName() {

                        return stdName;
                }


                /**
                 * Gets the Elliptic Curve parameter specification for this
                 * cryptographic curve.
                 *
                 * @return The EC parameter specification, {@code null} if this
                 *         cryptographic curve has no standard (JCA) name 
                 *         specified or if lookup of the EC parameters failed.
                 */
                public ECParameterSpec toECParameterSpec() {

                        if (stdName == null) {
                                return null;
                        }

                        ECNamedCurveParameterSpec curveParams = 
                                ECNamedCurveTable.getParameterSpec(stdName);

                        if (curveParams == null) {
                                return null;
                        }

                        return new ECNamedCurveSpec(curveParams.getName(),
                                                    curveParams.getCurve(),
                                                    curveParams.getG(),
                                                    curveParams.getN());
                }


                /**
                 * @see #getName
                 */
                @Override
                public String toString() {

                        return getName();
                }


                /**
                 * Overrides {@code Object.equals()}.
                 *
                 * @param object The object to compare to.
                 *
                 * @return {@code true} if the objects have the same value,
                 *         otherwise {@code false}.
                 */
                @Override
                public boolean equals(final Object object) {

                        return object instanceof Curve &&
                               this.toString().equals(object.toString());
                }


                /**
                 * Parses a cryptographic curve from the specified string.
                 *
                 * @param s The string to parse. Must not be {@code null} or
                 *          empty.
                 *
                 * @return The cryptographic curve.
                 */
                public static Curve parse(final String s) {

                        if (s == null || s.trim().isEmpty()) {
                                throw new IllegalArgumentException("The cryptographic curve string must not be null or empty");
                        }

                        if (s.equals(P_256.getName())) {
                                return P_256;

                        } else if (s.equals(P_384.getName())) {
                                return P_384;

                        } else if (s.equals(P_521.getName())) {
                                return P_521;

                        } else {
                                return new Curve(s);
                        }
                }


                /**
                 * Gets the cryptographic curve for the specified standard 
                 * (JCA) name.
                 *
                 * @param stdName The standard (JCA) name. Must not be 
                 *                {@code null}.
                 *
                 * @throws IllegalArgumentException If no matching JOSE curve 
                 *                                  constant could be found.
                 */
                public static Curve forStdName(final String stdName) {

                        switch (stdName) {
                                case "secp256r1": return P_256;
                                case "secp384r1": return P_384;
                                case "secp521r1": return P_521;
                                default: throw new IllegalArgumentException("No matching curve constant for standard (JCA) name " + stdName);
                        }
                }
        }


        /**
         * Builder for constructing Elliptic Curve JWKs.
         *
         * <p>Example use:
         *
         * <pre>
         * ECKey key = new ECKey.Builder(Curve.P521, x, y).
         *             d(d).
         *             algorithm(JWSAlgorithm.ES512).
         *             keyID("789").
         *             build();
         * </pre>
         */
        public static class Builder {


                /**
                 * The curve name.
                 */
                private final Curve crv;


                /**
                 * The public 'x' EC coordinate.
                 */
                private final Base64URL x;


                /**
                 * The public 'y' EC coordinate.
                 */
                private final Base64URL y;
                

                /**
                 * The private 'd' EC coordinate, optional.
                 */
                private Base64URL d;


                /**
                 * The key use, optional.
                 */
                private KeyUse use;


                /**
                 * The key operations, optional.
                 */
                private Set<KeyOperation> ops;


                /**
                 * The intended JOSE algorithm for the key, optional.
                 */
                private Algorithm alg;


                /**
                 * The key ID, optional.
                 */
                private String kid;


                /**
                 * X.509 certificate URL, optional.
                 */
                private URL x5u;


                /**
                 * X.509 certificate thumbprint, optional.
                 */
                private Base64URL x5t;


                /**
                 * The X.509 certificate chain, optional.
                 */
                private List<Base64> x5c;


                /**
                 * Creates a new Elliptic Curve JWK builder.
                 *
                 * @param crv The cryptographic curve. Must not be 
                 *            {@code null}.
                 * @param x   The public 'x' coordinate for the elliptic curve 
                 *            point. It is represented as the Base64URL 
                 *            encoding of the coordinate's big endian 
                 *            representation. Must not be {@code null}.
                 * @param y   The public 'y' coordinate for the elliptic curve 
                 *            point. It is represented as the Base64URL 
                 *            encoding of the coordinate's big endian 
                 *            representation. Must not be {@code null}.
                 */
                public Builder(final Curve crv, final Base64URL x, final Base64URL y) {

                        if (crv == null) {
                                throw new IllegalArgumentException("The curve must not be null");
                        }

                        this.crv = crv;

                        if (x == null) {
                                throw new IllegalArgumentException("The 'x' coordinate must not be null");
                        }

                        this.x = x;

                        if (y == null) {
                                throw new IllegalArgumentException("The 'y' coordinate must not be null");
                        }

                        this.y = y;
                }


                /**
                 * Creates a new Elliptic Curve JWK builder.
                 *
                 * @param crv The cryptographic curve. Must not be 
                 *            {@code null}.
                 * @param pub The public EC key to represent. Must not be 
                 *            {@code null}.
                 */
                public Builder(final Curve crv, final ECPublicKey pub) {

                        this(crv,
                             encodeCoordinate(pub.getParams().getCurve().getField().getFieldSize(), pub.getW().getAffineX()),
                             encodeCoordinate(pub.getParams().getCurve().getField().getFieldSize(), pub.getW().getAffineY()));
                }


                /**
                 * Sets the private 'd' coordinate for the elliptic curve 
                 * point. The alternative method is {@link #privateKey}.
                 *
                 * @param d The 'd' coordinate. It is represented as the 
                 *          Base64URL encoding of the coordinate's big endian 
                 *          representation. {@code null} if not specified (for
                 *          a public key).
                 *
                 * @return This builder.
                 */
                public Builder d(final Base64URL d) {

                        this.d = d;
                        return this;
                }


                /**
                 * Sets the private Elliptic Curve key. The alternative method 
                 * is {@link #d}.
                 *
                 * @param priv The private EC key, used to obtain the private
                 *             'd' coordinate for the elliptic curve point.
                 *             {@code null} if not specified (for a public 
                 *             key).
                 *
                 * @return This builder.
                 */
                public Builder privateKey(final ECPrivateKey priv) {

                        if (priv != null) {
                                this.d = encodeCoordinate(priv.getParams().getCurve().getField().getFieldSize(), priv.getS());
                        }
                        
                        return this;
                }


                /**
                 * Sets the use ({@code use}) of the JWK.
                 *
                 * @param use The key use, {@code null} if not specified or if 
                 *            the key is intended for signing as well as 
                 *            encryption.
                 *
                 * @return This builder.
                 */
                public Builder keyUse(final KeyUse use) {

                        this.use = use;
                        return this;
                }


                /**
                 * Sets the operations ({@code key_ops}) of the JWK.
                 *
                 * @param ops The key operations, {@code null} if not
                 *            specified.
                 *
                 * @return This builder.
                 */
                public Builder keyOperations(final Set<KeyOperation> ops) {

                        this.ops = ops;
                        return this;
                }


                /**
                 * Sets the intended JOSE algorithm ({@code alg}) for the JWK.
                 *
                 * @param alg The intended JOSE algorithm, {@code null} if not 
                 *            specified.
                 *
                 * @return This builder.
                 */
                public Builder algorithm(final Algorithm alg) {

                        this.alg = alg;
                        return this;
                }

                /**
                 * Sets the ID ({@code kid}) of the JWK. The key ID can be used 
                 * to match a specific key. This can be used, for instance, to 
                 * choose a key within a {@link JWKSet} during key rollover. 
                 * The key ID may also correspond to a JWS/JWE {@code kid} 
                 * header parameter value.
                 *
                 * @param kid The key ID, {@code null} if not specified.
                 *
                 * @return This builder.
                 */
                public Builder keyID(final String kid) {

                        this.kid = kid;
                        return this;
                }


                /**
                 * Sets the X.509 certificate URL ({@code x5u}) of the JWK.
                 *
                 * @param x5u The X.509 certificate URL, {@code null} if not 
                 *            specified.
                 *
                 * @return This builder.
                 */
                public Builder x509CertURL(final URL x5u) {

                        this.x5u = x5u;
                        return this;
                }


                /**
                 * Sets the X.509 certificate thumbprint ({@code x5t}) of the
                 * JWK.
                 *
                 * @param x5t The X.509 certificate thumbprint, {@code null} if 
                 *            not specified.
                 *
                 * @return This builder.
                 */
                public Builder x509CertThumbprint(final Base64URL x5t) {

                        this.x5t = x5t;
                        return this;
                }


                /**
                 * Sets the X.509 certificate chain ({@code x5c}) of the JWK.
                 *
                 * @param x5c The X.509 certificate chain as a unmodifiable 
                 *            list, {@code null} if not specified.
                 *
                 * @return This builder.
                 */
                public Builder x509CertChain(final List<Base64> x5c) {

                        this.x5c = x5c;
                        return this;
                }


                /**
                 * Builds a new octet sequence JWK.
                 *
                 * @return The octet sequence JWK.
                 *
                 * @throws IllegalStateException If the JWK parameters were
                 *                               inconsistently specified.
                 */
                public ECKey build() {

                        try {
                                if (d == null) {
                                        // Public key
                                        return new ECKey(crv, x, y, use, ops, alg, kid, x5u, x5t, x5c);
                                }

                                // Pair
                                return new ECKey(crv, x, y, d, use, ops, alg, kid, x5u, x5t, x5c);

                        } catch (IllegalArgumentException e) {

                                throw new IllegalStateException(e.getMessage(), e);
                        }
                }
        }


        /**
         * Returns the Base64URL encoding of the specified elliptic curve 'x',
         * 'y' or 'd' coordinate, with leading zero padding up to the specified
         * field size in bits.
         *
         * @param fieldSize  The field size in bits.
         * @param coordinate The elliptic curve coordinate. Must not be
         *                   {@code null}.
         *
         * @return The Base64URL-encoded coordinate, with leading zero padding
         *         up to the curve's field size.
         */
        public static Base64URL encodeCoordinate(final int fieldSize, final BigInteger coordinate) {

                byte[] unpadded = BigIntegerUtils.toBytesUnsigned(coordinate);

                int bytesToOutput = (fieldSize + 7)/8;

                if (unpadded.length >= bytesToOutput) {
                        // Greater-than check to prevent exception on malformed
                        // key below
                        return Base64URL.encode(unpadded);
                }

                byte[] padded = new byte[bytesToOutput];

                System.arraycopy(unpadded, 0, padded, bytesToOutput - unpadded.length, unpadded.length);

                return Base64URL.encode(padded);
        }


        /**
         * The curve name.
         */
        private final Curve crv;


        /**
         * The public 'x' EC coordinate.
         */
        private final Base64URL x;


        /**
         * The public 'y' EC coordinate.
         */
        private final Base64URL y;
        

        /**
         * The private 'd' EC coordinate
         */
        private final Base64URL d;


        /**
         * Creates a new public Elliptic Curve JSON Web Key (JWK) with the 
         * specified parameters.
         *
         * @param crv The cryptographic curve. Must not be {@code null}.
         * @param x   The public 'x' coordinate for the elliptic curve point.
         *            It is represented as the Base64URL encoding of the 
         *            coordinate's big endian representation. Must not be 
         *            {@code null}.
         * @param y   The public 'y' coordinate for the elliptic curve point. 
         *            It is represented as the Base64URL encoding of the 
         *            coordinate's big endian representation. Must not be 
         *            {@code null}.
         * @param use The key use, {@code null} if not specified or if the key
         *            is intended for signing as well as encryption.
         * @param ops The key operations, {@code null} if not specified.
         * @param alg The intended JOSE algorithm for the key, {@code null} if
         *            not specified.
         * @param kid The key ID, {@code null} if not specified.
         * @param x5u The X.509 certificate URL, {@code null} if not specified.
         * @param x5t The X.509 certificate thumbprint, {@code null} if not
         *            specified.
         * @param x5c The X.509 certificate chain, {@code null} if not 
         *            specified.
         */
        public ECKey(final Curve crv, final Base64URL x, final Base64URL y, 
                     final KeyUse use, final Set<KeyOperation> ops, final Algorithm alg, final String kid,
                     final URL x5u, final Base64URL x5t, final List<Base64> x5c) {

                super(KeyType.EC, use, ops, alg, kid, x5u, x5t, x5c);

                if (crv == null) {
                        throw new IllegalArgumentException("The curve must not be null");
                }

                this.crv = crv;

                if (x == null) {
                        throw new IllegalArgumentException("The 'x' coordinate must not be null");
                }

                this.x = x;

                if (y == null) {
                        throw new IllegalArgumentException("The 'y' coordinate must not be null");
                }

                this.y = y;

                this.d = null;
        }


        /**
         * Creates a new public / private Elliptic Curve JSON Web Key (JWK) 
         * with the specified parameters.
         *
         * @param crv The cryptographic curve. Must not be {@code null}.
         * @param x   The public 'x' coordinate for the elliptic curve point.
         *            It is represented as the Base64URL encoding of the 
         *            coordinate's big endian representation. Must not be 
         *            {@code null}.
         * @param y   The public 'y' coordinate for the elliptic curve point. 
         *            It is represented as the Base64URL encoding of the 
         *            coordinate's big endian representation. Must not be 
         *            {@code null}.
         * @param d   The private 'd' coordinate for the elliptic curve point. 
         *            It is represented as the Base64URL encoding of the 
         *            coordinate's big endian representation. Must not be 
         *            {@code null}.
         * @param use The key use, {@code null} if not specified or if the key
         *            is intended for signing as well as encryption.
         * @param ops The key operations, {@code null} if not specified.
         * @param alg The intended JOSE algorithm for the key, {@code null} if
         *            not specified.
         * @param kid The key ID, {@code null} if not specified.
         * @param x5u The X.509 certificate URL, {@code null} if not specified.
         * @param x5t The X.509 certificate thumbprint, {@code null} if not
         *            specified.
         * @param x5c The X.509 certificate chain, {@code null} if not 
         *            specified.
         */
        public ECKey(final Curve crv, final Base64URL x, final Base64URL y, final Base64URL d,
                     final KeyUse use, final Set<KeyOperation> ops, final Algorithm alg, final String kid,
                     final URL x5u, final Base64URL x5t, final List<Base64> x5c) {

                super(KeyType.EC, use, ops, alg, kid, x5u, x5t, x5c);

                if (crv == null) {
                        throw new IllegalArgumentException("The curve must not be null");
                }

                this.crv = crv;

                if (x == null) {
                        throw new IllegalArgumentException("The 'x' coordinate must not be null");
                }

                this.x = x;

                if (y == null) {
                        throw new IllegalArgumentException("The 'y' coordinate must not be null");
                }

                this.y = y;
                
                if (d == null) {
                        throw new IllegalArgumentException("The 'd' coordinate must not be null");
                }

                this.d = d;
        }


        /**
         * Creates a new public Elliptic Curve JSON Web Key (JWK) with the 
         * specified parameters.
         *
         * @param crv The cryptographic curve. Must not be {@code null}.
         * @param pub The public EC key to represent. Must not be {@code null}.
         * @param use The key use, {@code null} if not specified or if the key
         *            is intended for signing as well as encryption.
         * @param ops The key operations, {@code null} if not specified.
         * @param alg The intended JOSE algorithm for the key, {@code null} if
         *            not specified.
         * @param kid The key ID, {@code null} if not specified.
         * @param x5u The X.509 certificate URL, {@code null} if not specified.
         * @param x5t The X.509 certificate thumbprint, {@code null} if not
         *            specified.
         * @param x5c The X.509 certificate chain, {@code null} if not 
         *            specified.
         */
        public ECKey(final Curve crv, final ECPublicKey pub, 
                     final KeyUse use, final Set<KeyOperation> ops, final Algorithm alg, final String kid,
                     final URL x5u, final Base64URL x5t, final List<Base64> x5c) {

                this(crv, 
                     encodeCoordinate(pub.getParams().getCurve().getField().getFieldSize(), pub.getW().getAffineX()),
                     encodeCoordinate(pub.getParams().getCurve().getField().getFieldSize(), pub.getW().getAffineY()),
                     use, ops, alg, kid,
                     x5u, x5t, x5c);
        }


        /**
         * Creates a new public / private Elliptic Curve JSON Web Key (JWK) 
         * with the specified parameters.
         *
         * @param crv  The cryptographic curve. Must not be {@code null}.
         * @param pub  The public EC key to represent. Must not be 
         *             {@code null}.
         * @param priv The private EC key to represent. Must not be 
         *             {@code null}.
         * @param use  The key use, {@code null} if not specified or if the key
         *             is intended for signing as well as encryption.
         * @param ops  The key operations, {@code null} if not specified.
         * @param alg  The intended JOSE algorithm for the key, {@code null} if
         *             not specified.
         * @param kid  The key ID, {@code null} if not specified.
         * @param x5u  The X.509 certificate URL, {@code null} if not 
         *             specified.
         * @param x5t  The X.509 certificate thumbprint, {@code null} if not
         *             specified.
         * @param x5c  The X.509 certificate chain, {@code null} if not 
         *             specified.
         */
        public ECKey(final Curve crv, final ECPublicKey pub, final ECPrivateKey priv, 
                     final KeyUse use, final Set<KeyOperation> ops, final Algorithm alg, final String kid,
                     final URL x5u, final Base64URL x5t, final List<Base64> x5c) {

                this(crv,
                     encodeCoordinate(pub.getParams().getCurve().getField().getFieldSize(), pub.getW().getAffineX()),
                     encodeCoordinate(pub.getParams().getCurve().getField().getFieldSize(), pub.getW().getAffineY()),
                     encodeCoordinate(priv.getParams().getCurve().getField().getFieldSize(), priv.getS()),
                     use, ops, alg, kid,
                     x5u, x5t, x5c);
        }


        /**
         * Gets the cryptographic curve.
         *
         * @return The cryptographic curve.
         */
        public Curve getCurve() {

                return crv;
        }


        /**
         * Gets the public 'x' coordinate for the elliptic curve point.
         *
         * @return The 'x' coordinate. It is represented as the Base64URL 
         *         encoding of the coordinate's big endian representation.
         */
        public Base64URL getX() {

                return x;
        }


        /**
         * Gets the public 'y' coordinate for the elliptic curve point.
         *
         * @return The 'y' coordinate. It is represented as the Base64URL 
         *         encoding of the coordinate's big endian representation.
         */
        public Base64URL getY() {

                return y;
        }

        
        /**
         * Gets the private 'd' coordinate for the elliptic curve point. It is 
         * represented as the Base64URL encoding of the coordinate's big endian 
         * representation.
         *
         * @return The 'd' coordinate.  It is represented as the Base64URL 
         *         encoding of the coordinate's big endian representation. 
         *         {@code null} if not specified (for a public key).
         */
        public Base64URL getD() {

                return d;
        }


        /**
         * Gets a new BouncyCastle.org EC key factory.
         *
         * @return The EC key factory.
         *
         * @throws NoSuchAlgorithmException If a JCA provider or algorithm 
         *                                  exception was encountered.
         */
        private static KeyFactory getECKeyFactory()
                throws NoSuchAlgorithmException {

                return KeyFactory.getInstance("EC", BouncyCastleProviderSingleton.getInstance());
        }


        /**
         * Returns a standard {@code java.security.interfaces.ECPublicKey} 
         * representation of this Elliptic Curve JWK.
         * 
         * @return The public Elliptic Curve key.
         * 
         * @throws NoSuchAlgorithmException If EC is not supported by the
         *                                  underlying Java Cryptography (JCA)
         *                                  provider.
         * @throws InvalidKeySpecException  If the JWK key parameters are 
         *                                  invalid for a public EC key.
         */
        public ECPublicKey toECPublicKey()
                throws NoSuchAlgorithmException, InvalidKeySpecException {

                ECParameterSpec spec = crv.toECParameterSpec();

                if (spec == null) {
                        throw new NoSuchAlgorithmException("Couldn't get EC parameter spec for curve " + crv);
                }

                ECPoint w = new ECPoint(x.decodeToBigInteger(), y.decodeToBigInteger());

                ECPublicKeySpec publicKeySpec = new ECPublicKeySpec(w, spec);

                KeyFactory keyFactory = getECKeyFactory();

                return (ECPublicKey)keyFactory.generatePublic(publicKeySpec);
        }
        

        /**
         * Returns a standard {@code java.security.interfaces.ECPrivateKey} 
         * representation of this Elliptic Curve JWK.
         * 
         * @return The private Elliptic Curve key, {@code null} if not 
         *         specified by this JWK.
         * 
         * @throws NoSuchAlgorithmException If EC is not supported by the
         *                                  underlying Java Cryptography (JCA)
         *                                  provider.
         * @throws InvalidKeySpecException  If the JWK key parameters are 
         *                                  invalid for a private EC key.
         */
        public ECPrivateKey toECPrivateKey()
                throws NoSuchAlgorithmException, InvalidKeySpecException {

                if (d == null) {
                        // No private 'd' param
                        return null;
                }

                ECParameterSpec spec = crv.toECParameterSpec();

                if (spec == null) {
                        throw new NoSuchAlgorithmException("Couldn't get EC parameter spec for curve " + crv);
                }

                ECPrivateKeySpec privateKeySpec = new ECPrivateKeySpec(d.decodeToBigInteger(), spec);

                KeyFactory keyFactory = getECKeyFactory();

                return (ECPrivateKey)keyFactory.generatePrivate(privateKeySpec);
        }
        

        /**
         * Returns a standard {@code java.security.KeyPair} representation of 
         * this Elliptic Curve JWK.
         * 
         * @return The Elliptic Curve key pair. The private Elliptic Curve key 
         *         will be {@code null} if not specified.
         * 
         * @throws NoSuchAlgorithmException If EC is not supported by the
         *                                  underlying Java Cryptography (JCA)
         *                                  provider.
         * @throws InvalidKeySpecException  If the JWK key parameters are 
         *                                  invalid for a public and / or 
         *                                  private EC key.
         */
        public KeyPair toKeyPair()
                throws NoSuchAlgorithmException, InvalidKeySpecException {

                return new KeyPair(toECPublicKey(), toECPrivateKey());          
        }


        @Override
        public boolean isPrivate() {

                return d != null;
        }

        
        /**
         * Returns a copy of this Elliptic Curve JWK with any private values 
         * removed.
         *
         * @return The copied public Elliptic Curve JWK.
         */
        @Override
        public ECKey toPublicJWK() {

                return new ECKey(getCurve(), getX(), getY(),
                                 getKeyUse(), getKeyOperations(), getAlgorithm(), getKeyID(),
                                 getX509CertURL(), getX509CertThumbprint(), getX509CertChain());
        }
        

        @Override
        public JSONObject toJSONObject() {

                JSONObject o = super.toJSONObject();

                // Append EC specific attributes
                o.put("crv", crv.toString());
                o.put("x", x.toString());
                o.put("y", y.toString());

                if (d != null) {
                        o.put("d", d.toString());
                }
                
                return o;
        }


        /**
         * Parses a public / private Elliptic Curve JWK from the specified JSON
         * object string representation.
         *
         * @param s The JSON object string to parse. Must not be {@code null}.
         *
         * @return The public / private Elliptic Curve JWK.
         *
         * @throws ParseException If the string couldn't be parsed to an
         *                        Elliptic Curve JWK.
         */
        public static ECKey parse(final String s)
                throws ParseException {

                return parse(JSONObjectUtils.parseJSONObject(s));
        }


        /**
         * Parses a public / private Elliptic Curve JWK from the specified JSON
         * object representation.
         *
         * @param jsonObject The JSON object to parse. Must not be 
         *                   {@code null}.
         *
         * @return The public / private Elliptic Curve JWK.
         *
         * @throws ParseException If the JSON object couldn't be parsed to an 
         *                        Elliptic Curve JWK.
         */
        public static ECKey parse(final JSONObject jsonObject)
                throws ParseException {

                // Parse the mandatory parameters first
                Curve crv = Curve.parse(JSONObjectUtils.getString(jsonObject, "crv"));
                Base64URL x = new Base64URL(JSONObjectUtils.getString(jsonObject, "x"));
                Base64URL y = new Base64URL(JSONObjectUtils.getString(jsonObject, "y"));

                // Check key type
                KeyType kty = KeyType.parse(JSONObjectUtils.getString(jsonObject, "kty"));

                if (kty != KeyType.EC) {
                        throw new ParseException("The key type \"kty\" must be EC", 0);
                }
                
                // Get optional private key
                Base64URL d = null;
                if (jsonObject.get("d") != null) {
                        d = new Base64URL(JSONObjectUtils.getString(jsonObject, "d"));
                }
                
                // Get optional key use
                KeyUse use = null;

                if (jsonObject.containsKey("use")) {
                        use = KeyUse.parse(JSONObjectUtils.getString(jsonObject, "use"));
                }

                // Get optional key operations
                Set<KeyOperation> ops = null;

                if (jsonObject.containsKey("key_ops")) {
                        ops = KeyOperation.parse(JSONObjectUtils.getStringList(jsonObject, "key_ops"));
                }

                // Get optional intended algorithm
                Algorithm alg = null;

                if (jsonObject.containsKey("alg")) {
                        alg = new Algorithm(JSONObjectUtils.getString(jsonObject, "alg"));
                }

                // Get optional key ID
                String kid = null;

                if (jsonObject.containsKey("kid")) {
                        kid = JSONObjectUtils.getString(jsonObject, "kid");
                }

                // Get optional X.509 cert URL
                URL x5u = null;

                if (jsonObject.containsKey("x5u")) {
                        x5u = JSONObjectUtils.getURL(jsonObject, "x5u");        
                }

                // Get optional X.509 cert thumbprint
                Base64URL x5t = null;

                if (jsonObject.containsKey("x5t")) {
                        x5t = new Base64URL(JSONObjectUtils.getString(jsonObject, "x5t"));
                }

                // Get optional X.509 cert chain
                List<Base64> x5c = null;

                if (jsonObject.containsKey("x5c")) {
                        x5c = X509CertChainUtils.parseX509CertChain(JSONObjectUtils.getJSONArray(jsonObject, "x5c"));   
                }

                try {
                        if (d == null) {
                                // Public key
                                return new ECKey(crv, x, y, use, ops, alg, kid, x5u, x5t, x5c);

                        } else {
                                // Key pair
                                return new ECKey(crv, x, y, d, use, ops, alg, kid, x5u, x5t, x5c);
                        }

                } catch (IllegalArgumentException ex) {

                        // Conflicting 'use' and 'key_ops'
                        throw new ParseException(ex.getMessage(), 0);
                }
        }
}