package com.nimbusds.jose.jwk;


import java.io.Serializable;
import java.math.BigInteger;
import java.net.URI;
import java.security.*;
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.List;
import java.util.LinkedHashMap;
import java.util.Set;

import com.nimbusds.jose.util.Base64;
import com.nimbusds.jose.util.Base64URL;
import com.nimbusds.jose.util.BigIntegerUtils;
import com.nimbusds.jose.util.JSONObjectUtils;
import net.jcip.annotations.Immutable;

import net.minidev.json.JSONObject;

import com.nimbusds.jose.Algorithm;
import com.nimbusds.jose.JOSEException;


/**
 * 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 2015-12-08
 */
@Immutable
public final class ECKey extends JWK implements AssymetricJWK {


        private static final long serialVersionUID = 1L;


        /**
         * 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 implements Serializable {


                private static final long serialVersionUID = 1L;


                /**
                 * P-256 curve (secp256r1, also called prime256v1).
                 */
                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 curve name, {@code null} if not specified.
                 */
                private final String stdName;


                /**
                 * Creates a new cryptographic curve with the specified JOSE
                 * name. A standard curve name is not unspecified.
                 *
                 * @param name The JOSE 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 JOSE
                 * and standard names.
                 *
                 * @param name    The JOSE name of the cryptographic curve. 
                 *                Must not be {@code null}.
                 * @param stdName The standard 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 JOSE cryptographic curve name must not be null");
                        }

                        this.name = name;

                        this.stdName = stdName;
                }


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

                        return name;
                }


                /**
                 * Returns the standard name of this cryptographic curve.
                 *
                 * @return The standard name, {@code null} if not specified.
                 */
                public String getStdName() {

                        return stdName;
                }


                /**
                 * Returns the parameter specification for this cryptographic
                 * curve.
                 *
                 * @return The EC parameter specification, {@code null} if it
                 *         cannot be determined.
                 */
                public ECParameterSpec toECParameterSpec() {

                        return ECParameterTable.get(this);
                }


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

                        return getName();
                }


                @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
                 * name.
                 *
                 * @param stdName The standard curve name. May be {@code null}.
                 *
                 * @return The curve, {@code null} if it cannot be determined.
                 */
                public static Curve forStdName(final String stdName) {
                        if( "secp256r1".equals(stdName) || "prime256v1".equals(stdName)) {
                                 return P_256;
                        } else if( "secp384r1".equals(stdName) ) {
                                return P_384;
                        } else if( "secp521r1".equals(stdName) ) {
                                return P_521;
                        } else {
                                return null;
                        }
                }


                /**
                 * Gets the cryptographic curve for the specified parameter
                 * specification.
                 *
                 * @param spec The EC parameter spec. May be {@code null}.
                 *
                 * @return The curve, {@code null} if it cannot be determined.
                 */
                public static Curve forECParameterSpec(final ECParameterSpec spec) {

                        return ECParameterTable.get(spec);
                }
        }


        /**
         * Builder for constructing Elliptic Curve JWKs.
         *
         * <p>Example usage:
         *
         * <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 URI 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 ID ({@code kid}) of the JWK to its SHA-256 JWK
                 * thumbprint (RFC 7638). 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.
                 *
                 * @return This builder.
                 *
                 * @throws JOSEException If the SHA-256 hash algorithm is not
                 *                       supported.
                 */
                public Builder keyIDFromThumbprint()
                        throws JOSEException {

                        return keyIDFromThumbprint("SHA-256");
                }


                /**
                 * Sets the ID ({@code kid}) of the JWK to its JWK thumbprint
                 * (RFC 7638). 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 hashAlg The hash algorithm for the JWK thumbprint
                 *                computation. Must not be {@code null}.
                 *
                 * @return This builder.
                 *
                 * @throws JOSEException If the hash algorithm is not
                 *                       supported.
                 */
                public Builder keyIDFromThumbprint(final String hashAlg)
                        throws JOSEException {

                        // Put mandatory params in sorted order
                        LinkedHashMap<String,String> requiredParams = new LinkedHashMap<>();
                        requiredParams.put("crv", crv.toString());
                        requiredParams.put("kty", KeyType.EC.getValue());
                        requiredParams.put("x", x.toString());
                        requiredParams.put("y", y.toString());
                        this.kid = ThumbprintUtils.compute(hashAlg, requiredParams).toString();
                        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 URI 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 URI 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 URI 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 URI 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 URI 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;
        }


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

                return toECPublicKey(null);
        }


        /**
         * Returns a standard {@code java.security.interfaces.ECPublicKey}
         * representation of this Elliptic Curve JWK.
         *
         * @param provider The specific JCA provider to use, {@code null}
         *                 implies the default one.
         *
         * @return The public Elliptic Curve key.
         *
         * @throws JOSEException If EC is not supported by the underlying Java
         *                       Cryptography (JCA) provider or if the JWK
         *                       parameters are invalid for a public EC key.
         */
        public ECPublicKey toECPublicKey(final Provider provider)
                throws JOSEException {

                ECParameterSpec spec = crv.toECParameterSpec();

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

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

                ECPublicKeySpec publicKeySpec = new ECPublicKeySpec(w, spec);

                try {
                        KeyFactory keyFactory;

                        if (provider == null) {
                                keyFactory = KeyFactory.getInstance("EC");
                        } else {
                                keyFactory = KeyFactory.getInstance("EC", provider);
                        }

                        return (ECPublicKey) keyFactory.generatePublic(publicKeySpec);

                } catch (NoSuchAlgorithmException | InvalidKeySpecException e) {

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

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

                return toECPrivateKey(null);
        }


        /**
         * Returns a standard {@code java.security.interfaces.ECPrivateKey}
         * representation of this Elliptic Curve JWK.
         *
         * @param provider The specific JCA provider to use, {@code null}
         *                 implies the default one.
         *
         * @return The private Elliptic Curve key, {@code null} if not
         *         specified by this JWK.
         *
         * @throws JOSEException If EC is not supported by the underlying Java
         *                       Cryptography (JCA) provider or if the JWK
         *                       parameters are invalid for a private EC key.
         */
        public ECPrivateKey toECPrivateKey(final Provider provider)
                throws JOSEException {

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

                ECParameterSpec spec = crv.toECParameterSpec();

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

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

                try {
                        KeyFactory keyFactory;

                        if (provider == null) {
                                keyFactory = KeyFactory.getInstance("EC");
                        } else {
                                keyFactory = KeyFactory.getInstance("EC", provider);
                        }

                        return (ECPrivateKey) keyFactory.generatePrivate(privateKeySpec);

                } catch (NoSuchAlgorithmException | InvalidKeySpecException e) {

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


        @Override
        public PublicKey toPublicKey()
                throws JOSEException {

                return toECPublicKey();
        }


        @Override
        public PrivateKey toPrivateKey()
                throws JOSEException {

                return toECPrivateKey();
        }
        

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

                return toKeyPair(null);
        }


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

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


        @Override
        public LinkedHashMap<String,?> getRequiredParams() {

                // Put mandatory params in sorted order
                LinkedHashMap<String,String> requiredParams = new LinkedHashMap<>();
                requiredParams.put("crv", crv.toString());
                requiredParams.put("kty", getKeyType().getValue());
                requiredParams.put("x", x.toString());
                requiredParams.put("y", y.toString());
                return requiredParams;
        }


        @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.parse(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 = JWKMetadata.parseKeyType(jsonObject);

                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"));
                }


                try {
                        if (d == null) {
                                // Public key
                                return new ECKey(crv, x, y,
                                        JWKMetadata.parseKeyUse(jsonObject),
                                        JWKMetadata.parseKeyOperations(jsonObject),
                                        JWKMetadata.parseAlgorithm(jsonObject),
                                        JWKMetadata.parseKeyID(jsonObject),
                                        JWKMetadata.parseX509CertURL(jsonObject),
                                        JWKMetadata.parseX509CertThumbprint(jsonObject),
                                        JWKMetadata.parseX509CertChain(jsonObject));

                        } else {
                                // Key pair
                                return new ECKey(crv, x, y, d,
                                        JWKMetadata.parseKeyUse(jsonObject),
                                        JWKMetadata.parseKeyOperations(jsonObject),
                                        JWKMetadata.parseAlgorithm(jsonObject),
                                        JWKMetadata.parseKeyID(jsonObject),
                                        JWKMetadata.parseX509CertURL(jsonObject),
                                        JWKMetadata.parseX509CertThumbprint(jsonObject),
                                        JWKMetadata.parseX509CertChain(jsonObject));
                        }

                } catch (IllegalArgumentException ex) {

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