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 * Copyright (c) 1996, 2018, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * accompanied this code).
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 *
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package java.security;

import java.security.spec.AlgorithmParameterSpec;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.io.*;
import java.security.cert.Certificate;
import java.security.cert.X509Certificate;

import java.nio.ByteBuffer;

import java.security.Provider.Service;

import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.BadPaddingException;
import javax.crypto.NoSuchPaddingException;
import jdk.internal.misc.JavaSecuritySignatureAccess;
import jdk.internal.misc.SharedSecrets;

import sun.security.util.Debug;
import sun.security.jca.*;
import sun.security.jca.GetInstance.Instance;

The Signature class is used to provide applications the functionality
of a digital signature algorithm. Digital signatures are used for
authentication and integrity assurance of digital data.
 The signature algorithm can be, among others, the NIST standard DSA, using DSA and SHA-256. The DSA algorithm using the SHA-256 message digest algorithm can be specified as SHA256withDSA. In the case of RSA the signing algorithm could be specified as, for example, SHA256withRSA. The algorithm name must be specified, as there is no default. 
 A Signature object can be used to generate and verify digital
signatures.
 There are three phases to the use of a Signature object for
either signing data or verifying a signature:

Initialization, with either
    

    
a public key, which initializes the signature for verification (see initVerify), or 
a private key (and optionally a Secure Random Number Generator), which initializes the signature for signing (see initSign(PrivateKey) and initSign(PrivateKey, SecureRandom)). 
Updating
Depending on the type of initialization, this will update the bytes to be signed or verified. See the update methods. 
Signing or Verifying a signature on all updated bytes. See the sign methods and the verify method. 
Note that this class is abstract and extends from SignatureSpi for historical reasons. Application developers should only take notice of the methods defined in this Signature class; all the methods in the superclass are intended for cryptographic service providers who wish to supply their own implementations of digital signature algorithms. 
 Every implementation of the Java platform is required to support the following standard Signature algorithms: 

SHA1withDSA
SHA256withDSA
SHA1withRSA
SHA256withRSA

These algorithms are described in the 
Signature section of the
Java Security Standard Algorithm Names Specification.
Consult the release documentation for your implementation to see if any
other algorithms are supported.
Author:
Benjamin Renaud
Since:
1.1/**
 * The Signature class is used to provide applications the functionality
 * of a digital signature algorithm. Digital signatures are used for
 * authentication and integrity assurance of digital data.
 *
 * <p> The signature algorithm can be, among others, the NIST standard
 * DSA, using DSA and SHA-256. The DSA algorithm using the
 * SHA-256 message digest algorithm can be specified as {@code SHA256withDSA}.
 * In the case of RSA the signing algorithm could be specified as, for example,
 * {@code SHA256withRSA}.
 * The algorithm name must be specified, as there is no default.
 *
 * <p> A Signature object can be used to generate and verify digital
 * signatures.
 *
 * <p> There are three phases to the use of a Signature object for
 * either signing data or verifying a signature:<ol>
 *
 * <li>Initialization, with either
 *
 *     <ul>
 *
 *     <li>a public key, which initializes the signature for
 *     verification (see {@link #initVerify(PublicKey) initVerify}), or
 *
 *     <li>a private key (and optionally a Secure Random Number Generator),
 *     which initializes the signature for signing
 *     (see {@link #initSign(PrivateKey)}
 *     and {@link #initSign(PrivateKey, SecureRandom)}).
 *
 *     </ul>
 *
 * <li>Updating
 *
 * <p>Depending on the type of initialization, this will update the
 * bytes to be signed or verified. See the
 * {@link #update(byte) update} methods.
 *
 * <li>Signing or Verifying a signature on all updated bytes. See the
 * {@link #sign() sign} methods and the {@link #verify(byte[]) verify}
 * method.
 *
 * </ol>
 *
 * <p>Note that this class is abstract and extends from
 * {@code SignatureSpi} for historical reasons.
 * Application developers should only take notice of the methods defined in
 * this {@code Signature} class; all the methods in
 * the superclass are intended for cryptographic service providers who wish to
 * supply their own implementations of digital signature algorithms.
 *
 * <p> Every implementation of the Java platform is required to support the
 * following standard {@code Signature} algorithms:
 * <ul>
 * <li>{@code SHA1withDSA}</li>
 * <li>{@code SHA256withDSA}</li>
 * <li>{@code SHA1withRSA}</li>
 * <li>{@code SHA256withRSA}</li>
 * </ul>
 * These algorithms are described in the <a href=
 * "{@docRoot}/../specs/security/standard-names.html#signature-algorithms">
 * Signature section</a> of the
 * Java Security Standard Algorithm Names Specification.
 * Consult the release documentation for your implementation to see if any
 * other algorithms are supported.
 *
 * @author Benjamin Renaud
 * @since 1.1
 *
 */

public abstract class Signature extends SignatureSpi {

    static {
        SharedSecrets.setJavaSecuritySignatureAccess(
            new JavaSecuritySignatureAccess() {
                @Override
                public void initVerify(Signature s, PublicKey publicKey,
                        AlgorithmParameterSpec params)
                        throws InvalidKeyException,
                        InvalidAlgorithmParameterException {
                    s.initVerify(publicKey, params);
                }
                @Override
                public void initVerify(Signature s,
                        java.security.cert.Certificate certificate,
                        AlgorithmParameterSpec params)
                        throws InvalidKeyException,
                        InvalidAlgorithmParameterException {
                    s.initVerify(certificate, params);
                }
                @Override
                public void initSign(Signature s, PrivateKey privateKey,
                        AlgorithmParameterSpec params, SecureRandom random)
                        throws InvalidKeyException,
                        InvalidAlgorithmParameterException {
                    s.initSign(privateKey, params, random);
                }
        });
    }

    private static final Debug debug =
                        Debug.getInstance("jca", "Signature");

    private static final Debug pdebug =
                        Debug.getInstance("provider", "Provider");
    private static final boolean skipDebug =
        Debug.isOn("engine=") && !Debug.isOn("signature");

    /*
     * The algorithm for this signature object.
     * This value is used to map an OID to the particular algorithm.
     * The mapping is done in AlgorithmObject.algOID(String algorithm)
     */
    private String algorithm;

    // The provider
    Provider provider;

    
Possible state value, signifying that this signature object has not yet been initialized. /**
     * Possible {@link #state} value, signifying that
     * this signature object has not yet been initialized.
     */
    protected static final int UNINITIALIZED = 0;

    
Possible state value, signifying that this signature object has been initialized for signing. /**
     * Possible {@link #state} value, signifying that
     * this signature object has been initialized for signing.
     */
    protected static final int SIGN = 2;

    
Possible state value, signifying that this signature object has been initialized for verification. /**
     * Possible {@link #state} value, signifying that
     * this signature object has been initialized for verification.
     */
    protected static final int VERIFY = 3;

    
Current state of this signature object.
/**
     * Current state of this signature object.
     */
    protected int state = UNINITIALIZED;

    
Creates a Signature object for the specified algorithm.
Params:
algorithm – the standard string name of the algorithm.
See the Signature section in the 
Java Security Standard Algorithm Names Specification
for information about standard algorithm names./**
     * Creates a Signature object for the specified algorithm.
     *
     * @param algorithm the standard string name of the algorithm.
     * See the Signature section in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#signature-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard algorithm names.
     */
    protected Signature(String algorithm) {
        this.algorithm = algorithm;
    }

    // name of the special signature alg
    private static final String RSA_SIGNATURE = "NONEwithRSA";

    // name of the equivalent cipher alg
    private static final String RSA_CIPHER = "RSA/ECB/PKCS1Padding";

    // all the services we need to lookup for compatibility with Cipher
    private static final List<ServiceId> rsaIds = List.of(
        new ServiceId("Signature", "NONEwithRSA"),
        new ServiceId("Cipher", "RSA/ECB/PKCS1Padding"),
        new ServiceId("Cipher", "RSA/ECB"),
        new ServiceId("Cipher", "RSA//PKCS1Padding"),
        new ServiceId("Cipher", "RSA"));

    
Returns a Signature object that implements the specified signature
algorithm.
 This method traverses the list of registered security Providers,
starting with the most preferred Provider.
A new Signature object encapsulating the
SignatureSpi implementation from the first
Provider that supports the specified algorithm is returned.
 Note that the list of registered providers may be retrieved via the Security.getProviders() method. 
Params:
algorithm – the standard name of the algorithm requested.
See the Signature section in the 
Java Security Standard Algorithm Names Specification
for information about standard algorithm names.
Throws:
NoSuchAlgorithmException – if no Provider supports a Signature implementation for the specified algorithm
NullPointerException – if algorithm is null
See Also:
Provider
Implementation Note:
 The JDK Reference Implementation additionally uses the jdk.security.provider.preferred Security property to determine the preferred provider order for the specified algorithm. This may be different than the order of providers returned by Security.getProviders().
Returns:
the new Signature object/**
     * Returns a Signature object that implements the specified signature
     * algorithm.
     *
     * <p> This method traverses the list of registered security Providers,
     * starting with the most preferred Provider.
     * A new Signature object encapsulating the
     * SignatureSpi implementation from the first
     * Provider that supports the specified algorithm is returned.
     *
     * <p> Note that the list of registered providers may be retrieved via
     * the {@link Security#getProviders() Security.getProviders()} method.
     *
     * @implNote
     * The JDK Reference Implementation additionally uses the
     * {@code jdk.security.provider.preferred}
     * {@link Security#getProperty(String) Security} property to determine
     * the preferred provider order for the specified algorithm. This
     * may be different than the order of providers returned by
     * {@link Security#getProviders() Security.getProviders()}.
     *
     * @param algorithm the standard name of the algorithm requested.
     * See the Signature section in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#signature-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard algorithm names.
     *
     * @return the new {@code Signature} object
     *
     * @throws NoSuchAlgorithmException if no {@code Provider} supports a
     *         {@code Signature} implementation for the
     *         specified algorithm
     *
     * @throws NullPointerException if {@code algorithm} is {@code null}
     *
     * @see Provider
     */
    public static Signature getInstance(String algorithm)
            throws NoSuchAlgorithmException {
        Objects.requireNonNull(algorithm, "null algorithm name");
        List<Service> list;
        if (algorithm.equalsIgnoreCase(RSA_SIGNATURE)) {
            list = GetInstance.getServices(rsaIds);
        } else {
            list = GetInstance.getServices("Signature", algorithm);
        }
        Iterator<Service> t = list.iterator();
        if (t.hasNext() == false) {
            throw new NoSuchAlgorithmException
                (algorithm + " Signature not available");
        }
        // try services until we find an Spi or a working Signature subclass
        NoSuchAlgorithmException failure;
        do {
            Service s = t.next();
            if (isSpi(s)) {
                return new Delegate(s, t, algorithm);
            } else {
                // must be a subclass of Signature, disable dynamic selection
                try {
                    Instance instance =
                        GetInstance.getInstance(s, SignatureSpi.class);
                    return getInstance(instance, algorithm);
                } catch (NoSuchAlgorithmException e) {
                    failure = e;
                }
            }
        } while (t.hasNext());
        throw failure;
    }

    private static Signature getInstance(Instance instance, String algorithm) {
        Signature sig;
        if (instance.impl instanceof Signature) {
            sig = (Signature)instance.impl;
            sig.algorithm = algorithm;
        } else {
            SignatureSpi spi = (SignatureSpi)instance.impl;
            sig = new Delegate(spi, algorithm);
        }
        sig.provider = instance.provider;
        return sig;
    }

    private static final Map<String,Boolean> signatureInfo;

    static {
        signatureInfo = new ConcurrentHashMap<>();
        Boolean TRUE = Boolean.TRUE;
        // pre-initialize with values for our SignatureSpi implementations
        signatureInfo.put("sun.security.provider.DSA$RawDSA", TRUE);
        signatureInfo.put("sun.security.provider.DSA$SHA1withDSA", TRUE);
        signatureInfo.put("sun.security.rsa.RSASignature$MD2withRSA", TRUE);
        signatureInfo.put("sun.security.rsa.RSASignature$MD5withRSA", TRUE);
        signatureInfo.put("sun.security.rsa.RSASignature$SHA1withRSA", TRUE);
        signatureInfo.put("sun.security.rsa.RSASignature$SHA256withRSA", TRUE);
        signatureInfo.put("sun.security.rsa.RSASignature$SHA384withRSA", TRUE);
        signatureInfo.put("sun.security.rsa.RSASignature$SHA512withRSA", TRUE);
        signatureInfo.put("sun.security.rsa.RSAPSSSignature", TRUE);
        signatureInfo.put("com.sun.net.ssl.internal.ssl.RSASignature", TRUE);
        signatureInfo.put("sun.security.pkcs11.P11Signature", TRUE);
    }

    private static boolean isSpi(Service s) {
        if (s.getType().equals("Cipher")) {
            // must be a CipherSpi, which we can wrap with the CipherAdapter
            return true;
        }
        String className = s.getClassName();
        Boolean result = signatureInfo.get(className);
        if (result == null) {
            try {
                Object instance = s.newInstance(null);
                // Signature extends SignatureSpi
                // so it is a "real" Spi if it is an
                // instance of SignatureSpi but not Signature
                boolean r = (instance instanceof SignatureSpi)
                                && (instance instanceof Signature == false);
                if ((debug != null) && (r == false)) {
                    debug.println("Not a SignatureSpi " + className);
                    debug.println("Delayed provider selection may not be "
                        + "available for algorithm " + s.getAlgorithm());
                }
                result = Boolean.valueOf(r);
                signatureInfo.put(className, result);
            } catch (Exception e) {
                // something is wrong, assume not an SPI
                return false;
            }
        }
        return result.booleanValue();
    }

    
Returns a Signature object that implements the specified signature
algorithm.
 A new Signature object encapsulating the
SignatureSpi implementation from the specified provider
is returned.  The specified provider must be registered
in the security provider list.
 Note that the list of registered providers may be retrieved via the Security.getProviders() method. 
Params:
algorithm – the name of the algorithm requested.
See the Signature section in the 
Java Security Standard Algorithm Names Specification
for information about standard algorithm names.
provider – the name of the provider.
Throws:
IllegalArgumentException – if the provider name is null or empty
NoSuchAlgorithmException – if a SignatureSpi implementation for the specified algorithm is not available from the specified provider
NoSuchProviderException – if the specified provider is not
        registered in the security provider list
NullPointerException – if algorithm is null
See Also:
Provider
Returns:
the new Signature object/**
     * Returns a Signature object that implements the specified signature
     * algorithm.
     *
     * <p> A new Signature object encapsulating the
     * SignatureSpi implementation from the specified provider
     * is returned.  The specified provider must be registered
     * in the security provider list.
     *
     * <p> Note that the list of registered providers may be retrieved via
     * the {@link Security#getProviders() Security.getProviders()} method.
     *
     * @param algorithm the name of the algorithm requested.
     * See the Signature section in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#signature-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard algorithm names.
     *
     * @param provider the name of the provider.
     *
     * @return the new {@code Signature} object
     *
     * @throws IllegalArgumentException if the provider name is {@code null}
     *         or empty
     *
     * @throws NoSuchAlgorithmException if a {@code SignatureSpi}
     *         implementation for the specified algorithm is not
     *         available from the specified provider
     *
     * @throws NoSuchProviderException if the specified provider is not
     *         registered in the security provider list
     *
     * @throws NullPointerException if {@code algorithm} is {@code null}
     *
     * @see Provider
     */
    public static Signature getInstance(String algorithm, String provider)
            throws NoSuchAlgorithmException, NoSuchProviderException {
        Objects.requireNonNull(algorithm, "null algorithm name");
        if (algorithm.equalsIgnoreCase(RSA_SIGNATURE)) {
            // exception compatibility with existing code
            if (provider == null || provider.isEmpty()) {
                throw new IllegalArgumentException("missing provider");
            }
            Provider p = Security.getProvider(provider);
            if (p == null) {
                throw new NoSuchProviderException
                    ("no such provider: " + provider);
            }
            return getInstanceRSA(p);
        }
        Instance instance = GetInstance.getInstance
                ("Signature", SignatureSpi.class, algorithm, provider);
        return getInstance(instance, algorithm);
    }

    
Returns a Signature object that implements the specified
signature algorithm.
 A new Signature object encapsulating the
SignatureSpi implementation from the specified Provider
object is returned.  Note that the specified Provider object
does not have to be registered in the provider list.
Params:
algorithm – the name of the algorithm requested.
See the Signature section in the 
Java Security Standard Algorithm Names Specification
for information about standard algorithm names.
provider – the provider.
Throws:
IllegalArgumentException – if the provider is null
NoSuchAlgorithmException – if a SignatureSpi implementation for the specified algorithm is not available from the specified Provider object
NullPointerException – if algorithm is null
See Also:
Provider
Returns:
the new Signature object
Since:
1.4/**
     * Returns a Signature object that implements the specified
     * signature algorithm.
     *
     * <p> A new Signature object encapsulating the
     * SignatureSpi implementation from the specified Provider
     * object is returned.  Note that the specified Provider object
     * does not have to be registered in the provider list.
     *
     * @param algorithm the name of the algorithm requested.
     * See the Signature section in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#signature-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard algorithm names.
     *
     * @param provider the provider.
     *
     * @return the new {@code Signature} object
     *
     * @throws IllegalArgumentException if the provider is {@code null}
     *
     * @throws NoSuchAlgorithmException if a {@code SignatureSpi}
     *         implementation for the specified algorithm is not available
     *         from the specified {@code Provider} object
     *
     * @throws NullPointerException if {@code algorithm} is {@code null}
     *
     * @see Provider
     *
     * @since 1.4
     */
    public static Signature getInstance(String algorithm, Provider provider)
            throws NoSuchAlgorithmException {
        Objects.requireNonNull(algorithm, "null algorithm name");
        if (algorithm.equalsIgnoreCase(RSA_SIGNATURE)) {
            // exception compatibility with existing code
            if (provider == null) {
                throw new IllegalArgumentException("missing provider");
            }
            return getInstanceRSA(provider);
        }
        Instance instance = GetInstance.getInstance
                ("Signature", SignatureSpi.class, algorithm, provider);
        return getInstance(instance, algorithm);
    }

    // return an implementation for NONEwithRSA, which is a special case
    // because of the Cipher.RSA/ECB/PKCS1Padding compatibility wrapper
    private static Signature getInstanceRSA(Provider p)
            throws NoSuchAlgorithmException {
        // try Signature first
        Service s = p.getService("Signature", RSA_SIGNATURE);
        if (s != null) {
            Instance instance = GetInstance.getInstance(s, SignatureSpi.class);
            return getInstance(instance, RSA_SIGNATURE);
        }
        // check Cipher
        try {
            Cipher c = Cipher.getInstance(RSA_CIPHER, p);
            return new Delegate(new CipherAdapter(c), RSA_SIGNATURE);
        } catch (GeneralSecurityException e) {
            // throw Signature style exception message to avoid confusion,
            // but append Cipher exception as cause
            throw new NoSuchAlgorithmException("no such algorithm: "
                + RSA_SIGNATURE + " for provider " + p.getName(), e);
        }
    }

    
Returns the provider of this signature object.
Returns:
the provider of this signature object/**
     * Returns the provider of this signature object.
     *
     * @return the provider of this signature object
     */
    public final Provider getProvider() {
        chooseFirstProvider();
        return this.provider;
    }

    private String getProviderName() {
        return (provider == null)  ? "(no provider)" : provider.getName();
    }

    void chooseFirstProvider() {
        // empty, overridden in Delegate
    }

    
Initializes this object for verification. If this method is called
again with a different argument, it negates the effect
of this call.
Params:
publicKey – the public key of the identity whose signature is
going to be verified.
Throws:
InvalidKeyException – if the key is invalid./**
     * Initializes this object for verification. If this method is called
     * again with a different argument, it negates the effect
     * of this call.
     *
     * @param publicKey the public key of the identity whose signature is
     * going to be verified.
     *
     * @exception InvalidKeyException if the key is invalid.
     */
    public final void initVerify(PublicKey publicKey)
            throws InvalidKeyException {
        engineInitVerify(publicKey);
        state = VERIFY;

        if (!skipDebug && pdebug != null) {
            pdebug.println("Signature." + algorithm +
                " verification algorithm from: " + getProviderName());
        }
    }

    
Initialize this object for verification. If this method is called
again with different arguments, it negates the effect
of this call.
Params:
publicKey – the public key of the identity whose signature is
going to be verified.
params – the parameters used for verifying this signature.
Throws:
InvalidKeyException – if the key is invalid.
InvalidAlgorithmParameterException – if the params is invalid./**
     * Initialize this object for verification. If this method is called
     * again with different arguments, it negates the effect
     * of this call.
     *
     * @param publicKey the public key of the identity whose signature is
     * going to be verified.
     * @param params the parameters used for verifying this signature.
     *
     * @exception InvalidKeyException if the key is invalid.
     * @exception InvalidAlgorithmParameterException if the params is invalid.
     */
    final void initVerify(PublicKey publicKey, AlgorithmParameterSpec params)
            throws InvalidKeyException, InvalidAlgorithmParameterException {
        engineInitVerify(publicKey, params);
        state = VERIFY;

        if (!skipDebug && pdebug != null) {
            pdebug.println("Signature." + algorithm +
                " verification algorithm from: " + getProviderName());
        }
    }

    private static PublicKey getPublicKeyFromCert(Certificate cert)
            throws InvalidKeyException {
        // If the certificate is of type X509Certificate,
        // we should check whether it has a Key Usage
        // extension marked as critical.
        //if (cert instanceof java.security.cert.X509Certificate) {
        if (cert instanceof X509Certificate) {
            // Check whether the cert has a key usage extension
            // marked as a critical extension.
            // The OID for KeyUsage extension is 2.5.29.15.
            X509Certificate c = (X509Certificate)cert;
            Set<String> critSet = c.getCriticalExtensionOIDs();

            if (critSet != null && !critSet.isEmpty()
                && critSet.contains("2.5.29.15")) {
                boolean[] keyUsageInfo = c.getKeyUsage();
                // keyUsageInfo[0] is for digitalSignature.
                if ((keyUsageInfo != null) && (keyUsageInfo[0] == false))
                    throw new InvalidKeyException("Wrong key usage");
            }
        }
        return cert.getPublicKey();
    }

    
Initializes this object for verification, using the public key from
the given certificate.
If the certificate is of type X.509 and has a key usage
extension field marked as critical, and the value of the key usage extension field implies that the public key in the certificate and its corresponding private key are not supposed to be used for digital signatures, an InvalidKeyException is thrown. 
Params:
certificate – the certificate of the identity whose signature is
going to be verified.
Throws:
InvalidKeyException –  if the public key in the certificate
is not encoded properly or does not include required  parameter
information or cannot be used for digital signature purposes.
Since:
1.3/**
     * Initializes this object for verification, using the public key from
     * the given certificate.
     * <p>If the certificate is of type X.509 and has a <i>key usage</i>
     * extension field marked as critical, and the value of the <i>key usage</i>
     * extension field implies that the public key in
     * the certificate and its corresponding private key are not
     * supposed to be used for digital signatures, an
     * {@code InvalidKeyException} is thrown.
     *
     * @param certificate the certificate of the identity whose signature is
     * going to be verified.
     *
     * @exception InvalidKeyException  if the public key in the certificate
     * is not encoded properly or does not include required  parameter
     * information or cannot be used for digital signature purposes.
     * @since 1.3
     */
    public final void initVerify(Certificate certificate)
            throws InvalidKeyException {
        engineInitVerify(getPublicKeyFromCert(certificate));
        state = VERIFY;

        if (!skipDebug && pdebug != null) {
            pdebug.println("Signature." + algorithm +
                " verification algorithm from: " + getProviderName());
        }
    }

    
Initializes this object for verification, using the public key from
the given certificate.
If the certificate is of type X.509 and has a key usage
extension field marked as critical, and the value of the key usage extension field implies that the public key in the certificate and its corresponding private key are not supposed to be used for digital signatures, an InvalidKeyException is thrown. 
Params:
certificate – the certificate of the identity whose signature is
going to be verified.
params – the parameters used for verifying this signature.
Throws:
InvalidKeyException –  if the public key in the certificate
is not encoded properly or does not include required  parameter
information or cannot be used for digital signature purposes.
InvalidAlgorithmParameterException – if the params is invalid.
Since:
13/**
     * Initializes this object for verification, using the public key from
     * the given certificate.
     * <p>If the certificate is of type X.509 and has a <i>key usage</i>
     * extension field marked as critical, and the value of the <i>key usage</i>
     * extension field implies that the public key in
     * the certificate and its corresponding private key are not
     * supposed to be used for digital signatures, an
     * {@code InvalidKeyException} is thrown.
     *
     * @param certificate the certificate of the identity whose signature is
     * going to be verified.
     * @param params the parameters used for verifying this signature.
     *
     * @exception InvalidKeyException  if the public key in the certificate
     * is not encoded properly or does not include required  parameter
     * information or cannot be used for digital signature purposes.
     * @exception InvalidAlgorithmParameterException if the params is invalid.
     *
     * @since 13
     */
    final void initVerify(Certificate certificate,
            AlgorithmParameterSpec params)
            throws InvalidKeyException, InvalidAlgorithmParameterException {
        engineInitVerify(getPublicKeyFromCert(certificate), params);
        state = VERIFY;

        if (!skipDebug && pdebug != null) {
            pdebug.println("Signature." + algorithm +
                " verification algorithm from: " + getProviderName());
        }
    }

    
Initialize this object for signing. If this method is called
again with a different argument, it negates the effect
of this call.
Params:
privateKey – the private key of the identity whose signature
is going to be generated.
Throws:
InvalidKeyException – if the key is invalid./**
     * Initialize this object for signing. If this method is called
     * again with a different argument, it negates the effect
     * of this call.
     *
     * @param privateKey the private key of the identity whose signature
     * is going to be generated.
     *
     * @exception InvalidKeyException if the key is invalid.
     */
    public final void initSign(PrivateKey privateKey)
            throws InvalidKeyException {
        engineInitSign(privateKey);
        state = SIGN;

        if (!skipDebug && pdebug != null) {
            pdebug.println("Signature." + algorithm +
                " signing algorithm from: " + getProviderName());
        }
    }

    
Initialize this object for signing. If this method is called
again with a different argument, it negates the effect
of this call.
Params:
privateKey – the private key of the identity whose signature
is going to be generated.
random – the source of randomness for this signature.
Throws:
InvalidKeyException – if the key is invalid./**
     * Initialize this object for signing. If this method is called
     * again with a different argument, it negates the effect
     * of this call.
     *
     * @param privateKey the private key of the identity whose signature
     * is going to be generated.
     *
     * @param random the source of randomness for this signature.
     *
     * @exception InvalidKeyException if the key is invalid.
     */
    public final void initSign(PrivateKey privateKey, SecureRandom random)
            throws InvalidKeyException {
        engineInitSign(privateKey, random);
        state = SIGN;

        if (!skipDebug && pdebug != null) {
            pdebug.println("Signature." + algorithm +
                " signing algorithm from: " + getProviderName());
        }
    }

    
Initialize this object for signing. If this method is called
again with different arguments, it negates the effect
of this call.
Params:
privateKey – the private key of the identity whose signature
is going to be generated.
params – the parameters used for generating signature.
random – the source of randomness for this signature.
Throws:
InvalidKeyException – if the key is invalid.
InvalidAlgorithmParameterException – if the params is invalid/**
     * Initialize this object for signing. If this method is called
     * again with different arguments, it negates the effect
     * of this call.
     *
     * @param privateKey the private key of the identity whose signature
     * is going to be generated.
     * @param params the parameters used for generating signature.
     * @param random the source of randomness for this signature.
     *
     * @exception InvalidKeyException if the key is invalid.
     * @exception InvalidAlgorithmParameterException if the params is invalid
     */
    final void initSign(PrivateKey privateKey,
            AlgorithmParameterSpec params, SecureRandom random)
            throws InvalidKeyException, InvalidAlgorithmParameterException {
        engineInitSign(privateKey, params, random);
        state = SIGN;

        if (!skipDebug && pdebug != null) {
            pdebug.println("Signature." + algorithm +
                " signing algorithm from: " + getProviderName());
        }
    }

    
Returns the signature bytes of all the data updated.
The format of the signature depends on the underlying
signature scheme.
A call to this method resets this signature object to the state it was in when previously initialized for signing via a call to initSign(PrivateKey). That is, the object is reset and available to generate another signature from the same signer, if desired, via new calls to update and sign. 
Throws:
SignatureException – if this signature object is not
initialized properly or if this signature algorithm is unable to
process the input data provided.
Returns:
the signature bytes of the signing operation's result./**
     * Returns the signature bytes of all the data updated.
     * The format of the signature depends on the underlying
     * signature scheme.
     *
     * <p>A call to this method resets this signature object to the state
     * it was in when previously initialized for signing via a
     * call to {@code initSign(PrivateKey)}. That is, the object is
     * reset and available to generate another signature from the same
     * signer, if desired, via new calls to {@code update} and
     * {@code sign}.
     *
     * @return the signature bytes of the signing operation's result.
     *
     * @exception SignatureException if this signature object is not
     * initialized properly or if this signature algorithm is unable to
     * process the input data provided.
     */
    public final byte[] sign() throws SignatureException {
        if (state == SIGN) {
            return engineSign();
        }
        throw new SignatureException("object not initialized for " +
                                     "signing");
    }

    
Finishes the signature operation and stores the resulting signature bytes in the provided buffer outbuf, starting at offset. The format of the signature depends on the underlying signature scheme. 
This signature object is reset to its initial state (the state it was in after a call to one of the initSign methods) and can be reused to generate further signatures with the same private key. 
Params:
outbuf – buffer for the signature result.
offset – offset into outbuf where the signature is stored.
len – number of bytes within outbuf allotted for the signature.
Throws:
SignatureException – if this signature object is not initialized properly, if this signature algorithm is unable to process the input data provided, or if len is less than the actual signature length.
IllegalArgumentException – if outbuf is null, or offset or len is less than 0, or the sum of offset and len is greater than the length of outbuf.
Returns:
the number of bytes placed into outbuf.
Since:
1.2/**
     * Finishes the signature operation and stores the resulting signature
     * bytes in the provided buffer {@code outbuf}, starting at
     * {@code offset}.
     * The format of the signature depends on the underlying
     * signature scheme.
     *
     * <p>This signature object is reset to its initial state (the state it
     * was in after a call to one of the {@code initSign} methods) and
     * can be reused to generate further signatures with the same private key.
     *
     * @param outbuf buffer for the signature result.
     *
     * @param offset offset into {@code outbuf} where the signature is
     * stored.
     *
     * @param len number of bytes within {@code outbuf} allotted for the
     * signature.
     *
     * @return the number of bytes placed into {@code outbuf}.
     *
     * @exception SignatureException if this signature object is not
     *     initialized properly, if this signature algorithm is unable to
     *     process the input data provided, or if {@code len} is less
     *     than the actual signature length.
     * @exception IllegalArgumentException if {@code outbuf} is {@code null},
     *     or {@code offset} or {@code len} is less than 0, or the sum of
     *     {@code offset} and {@code len} is greater than the length of
     *     {@code outbuf}.
     *
     * @since 1.2
     */
    public final int sign(byte[] outbuf, int offset, int len)
        throws SignatureException {
        if (outbuf == null) {
            throw new IllegalArgumentException("No output buffer given");
        }
        if (offset < 0 || len < 0) {
            throw new IllegalArgumentException("offset or len is less than 0");
        }
        if (outbuf.length - offset < len) {
            throw new IllegalArgumentException
                ("Output buffer too small for specified offset and length");
        }
        if (state != SIGN) {
            throw new SignatureException("object not initialized for " +
                                         "signing");
        }
        return engineSign(outbuf, offset, len);
    }

    
Verifies the passed-in signature.
A call to this method resets this signature object to the state it was in when previously initialized for verification via a call to initVerify(PublicKey). That is, the object is reset and available to verify another signature from the identity whose public key was specified in the call to initVerify. 
Params:
signature – the signature bytes to be verified.
Throws:
SignatureException – if this signature object is not
initialized properly, the passed-in signature is improperly
encoded or of the wrong type, if this signature algorithm is unable to
process the input data provided, etc.
Returns:
true if the signature was verified, false if not./**
     * Verifies the passed-in signature.
     *
     * <p>A call to this method resets this signature object to the state
     * it was in when previously initialized for verification via a
     * call to {@code initVerify(PublicKey)}. That is, the object is
     * reset and available to verify another signature from the identity
     * whose public key was specified in the call to {@code initVerify}.
     *
     * @param signature the signature bytes to be verified.
     *
     * @return true if the signature was verified, false if not.
     *
     * @exception SignatureException if this signature object is not
     * initialized properly, the passed-in signature is improperly
     * encoded or of the wrong type, if this signature algorithm is unable to
     * process the input data provided, etc.
     */
    public final boolean verify(byte[] signature) throws SignatureException {
        if (state == VERIFY) {
            return engineVerify(signature);
        }
        throw new SignatureException("object not initialized for " +
                                     "verification");
    }

    
Verifies the passed-in signature in the specified array
of bytes, starting at the specified offset.
A call to this method resets this signature object to the state it was in when previously initialized for verification via a call to initVerify(PublicKey). That is, the object is reset and available to verify another signature from the identity whose public key was specified in the call to initVerify. 
Params:
signature – the signature bytes to be verified.
offset – the offset to start from in the array of bytes.
length – the number of bytes to use, starting at offset.
Throws:
SignatureException – if this signature object is not
initialized properly, the passed-in signature is improperly
encoded or of the wrong type, if this signature algorithm is unable to
process the input data provided, etc.
IllegalArgumentException – if the signature byte array is null, or the offset or length is less than 0, or the sum of the offset and length is greater than the length of the signature byte array.
Returns:
true if the signature was verified, false if not.
Since:
1.4/**
     * Verifies the passed-in signature in the specified array
     * of bytes, starting at the specified offset.
     *
     * <p>A call to this method resets this signature object to the state
     * it was in when previously initialized for verification via a
     * call to {@code initVerify(PublicKey)}. That is, the object is
     * reset and available to verify another signature from the identity
     * whose public key was specified in the call to {@code initVerify}.
     *
     *
     * @param signature the signature bytes to be verified.
     * @param offset the offset to start from in the array of bytes.
     * @param length the number of bytes to use, starting at offset.
     *
     * @return true if the signature was verified, false if not.
     *
     * @exception SignatureException if this signature object is not
     * initialized properly, the passed-in signature is improperly
     * encoded or of the wrong type, if this signature algorithm is unable to
     * process the input data provided, etc.
     * @exception IllegalArgumentException if the {@code signature}
     * byte array is {@code null}, or the {@code offset} or {@code length}
     * is less than 0, or the sum of the {@code offset} and
     * {@code length} is greater than the length of the
     * {@code signature} byte array.
     * @since 1.4
     */
    public final boolean verify(byte[] signature, int offset, int length)
        throws SignatureException {
        if (state == VERIFY) {
            if (signature == null) {
                throw new IllegalArgumentException("signature is null");
            }
            if (offset < 0 || length < 0) {
                throw new IllegalArgumentException
                    ("offset or length is less than 0");
            }
            if (signature.length - offset < length) {
                throw new IllegalArgumentException
                    ("signature too small for specified offset and length");
            }

            return engineVerify(signature, offset, length);
        }
        throw new SignatureException("object not initialized for " +
                                     "verification");
    }

    
Updates the data to be signed or verified by a byte.
Params:
b – the byte to use for the update.
Throws:
SignatureException – if this signature object is not
initialized properly./**
     * Updates the data to be signed or verified by a byte.
     *
     * @param b the byte to use for the update.
     *
     * @exception SignatureException if this signature object is not
     * initialized properly.
     */
    public final void update(byte b) throws SignatureException {
        if (state == VERIFY || state == SIGN) {
            engineUpdate(b);
        } else {
            throw new SignatureException("object not initialized for "
                                         + "signature or verification");
        }
    }

    
Updates the data to be signed or verified, using the specified
array of bytes.
Params:
data – the byte array to use for the update.
Throws:
SignatureException – if this signature object is not
initialized properly./**
     * Updates the data to be signed or verified, using the specified
     * array of bytes.
     *
     * @param data the byte array to use for the update.
     *
     * @exception SignatureException if this signature object is not
     * initialized properly.
     */
    public final void update(byte[] data) throws SignatureException {
        update(data, 0, data.length);
    }

    
Updates the data to be signed or verified, using the specified
array of bytes, starting at the specified offset.
Params:
data – the array of bytes.
off – the offset to start from in the array of bytes.
len – the number of bytes to use, starting at offset.
Throws:
SignatureException – if this signature object is not
    initialized properly.
IllegalArgumentException – if data is null, or off or len is less than 0, or the sum of off and len is greater than the length of data./**
     * Updates the data to be signed or verified, using the specified
     * array of bytes, starting at the specified offset.
     *
     * @param data the array of bytes.
     * @param off the offset to start from in the array of bytes.
     * @param len the number of bytes to use, starting at offset.
     *
     * @exception SignatureException if this signature object is not
     *     initialized properly.
     * @exception IllegalArgumentException if {@code data} is {@code null},
     *     or {@code off} or {@code len} is less than 0, or the sum of
     *     {@code off} and {@code len} is greater than the length of
     *     {@code data}.
     */
    public final void update(byte[] data, int off, int len)
            throws SignatureException {
        if (state == SIGN || state == VERIFY) {
            if (data == null) {
                throw new IllegalArgumentException("data is null");
            }
            if (off < 0 || len < 0) {
                throw new IllegalArgumentException("off or len is less than 0");
            }
            if (data.length - off < len) {
                throw new IllegalArgumentException
                    ("data too small for specified offset and length");
            }
            engineUpdate(data, off, len);
        } else {
            throw new SignatureException("object not initialized for "
                                         + "signature or verification");
        }
    }

    
Updates the data to be signed or verified using the specified ByteBuffer. Processes the data.remaining() bytes starting at data.position(). Upon return, the buffer's position will be equal to its limit; its limit will not have changed. 
Params:
data – the ByteBuffer
Throws:
SignatureException – if this signature object is not
initialized properly.
Since:
1.5/**
     * Updates the data to be signed or verified using the specified
     * ByteBuffer. Processes the {@code data.remaining()} bytes
     * starting at {@code data.position()}.
     * Upon return, the buffer's position will be equal to its limit;
     * its limit will not have changed.
     *
     * @param data the ByteBuffer
     *
     * @exception SignatureException if this signature object is not
     * initialized properly.
     * @since 1.5
     */
    public final void update(ByteBuffer data) throws SignatureException {
        if ((state != SIGN) && (state != VERIFY)) {
            throw new SignatureException("object not initialized for "
                                         + "signature or verification");
        }
        if (data == null) {
            throw new NullPointerException();
        }
        engineUpdate(data);
    }

    
Returns the name of the algorithm for this signature object.
Returns:
the name of the algorithm for this signature object./**
     * Returns the name of the algorithm for this signature object.
     *
     * @return the name of the algorithm for this signature object.
     */
    public final String getAlgorithm() {
        return this.algorithm;
    }

    
Returns a string representation of this signature object,
providing information that includes the state of the object
and the name of the algorithm used.
Returns:
a string representation of this signature object./**
     * Returns a string representation of this signature object,
     * providing information that includes the state of the object
     * and the name of the algorithm used.
     *
     * @return a string representation of this signature object.
     */
    public String toString() {
        String initState = "";
        switch (state) {
        case UNINITIALIZED:
            initState = "<not initialized>";
            break;
        case VERIFY:
            initState = "<initialized for verifying>";
            break;
        case SIGN:
            initState = "<initialized for signing>";
            break;
        }
        return "Signature object: " + getAlgorithm() + initState;
    }

    
Sets the specified algorithm parameter to the specified value.
This method supplies a general-purpose mechanism through
which it is possible to set the various parameters of this object.
A parameter may be any settable parameter for the algorithm, such as
a parameter size, or a source of random bits for signature generation
(if appropriate), or an indication of whether or not to perform
a specific but optional computation. A uniform algorithm-specific
naming scheme for each parameter is desirable but left unspecified
at this time.
Params:
param – the string identifier of the parameter.
value – the parameter value.
Throws:
InvalidParameterException – if param is an invalid parameter for this signature algorithm engine, the parameter is already set and cannot be set again, a security exception occurs, and so on.
See Also:
getParameter
Deprecated:
Use 
setParameter./**
     * Sets the specified algorithm parameter to the specified value.
     * This method supplies a general-purpose mechanism through
     * which it is possible to set the various parameters of this object.
     * A parameter may be any settable parameter for the algorithm, such as
     * a parameter size, or a source of random bits for signature generation
     * (if appropriate), or an indication of whether or not to perform
     * a specific but optional computation. A uniform algorithm-specific
     * naming scheme for each parameter is desirable but left unspecified
     * at this time.
     *
     * @param param the string identifier of the parameter.
     * @param value the parameter value.
     *
     * @exception InvalidParameterException if {@code param} is an
     * invalid parameter for this signature algorithm engine,
     * the parameter is already set
     * and cannot be set again, a security exception occurs, and so on.
     *
     * @see #getParameter
     *
     * @deprecated Use
     * {@link #setParameter(java.security.spec.AlgorithmParameterSpec)
     * setParameter}.
     */
    @Deprecated
    public final void setParameter(String param, Object value)
            throws InvalidParameterException {
        engineSetParameter(param, value);
    }

    
Initializes this signature engine with the specified parameter set.
Params:
params – the parameters
Throws:
InvalidAlgorithmParameterException – if the given parameters
are inappropriate for this signature engine
See Also:
getParameters/**
     * Initializes this signature engine with the specified parameter set.
     *
     * @param params the parameters
     *
     * @exception InvalidAlgorithmParameterException if the given parameters
     * are inappropriate for this signature engine
     *
     * @see #getParameters
     */
    public final void setParameter(AlgorithmParameterSpec params)
            throws InvalidAlgorithmParameterException {
        engineSetParameter(params);
    }

    
Returns the parameters used with this signature object.
 If this signature has been previously initialized with parameters (by calling the setParameter method), this method returns the same parameters. If this signature has not been initialized with parameters, this method may return a combination of default and randomly generated parameter values if the underlying signature implementation supports it and can successfully generate them. Otherwise, null is returned. 
See Also:
setParameter(AlgorithmParameterSpec)
Returns:
the parameters used with this signature, or null
Since:
1.4/**
     * Returns the parameters used with this signature object.
     *
     * <p> If this signature has been previously initialized with parameters
     * (by calling the {@code setParameter} method), this method returns
     * the same parameters. If this signature has not been initialized with
     * parameters, this method may return a combination of default and
     * randomly generated parameter values if the underlying
     * signature implementation supports it and can successfully generate
     * them. Otherwise, {@code null} is returned.
     *
     * @return the parameters used with this signature, or {@code null}
     *
     * @see #setParameter(AlgorithmParameterSpec)
     * @since 1.4
     */
    public final AlgorithmParameters getParameters() {
        return engineGetParameters();
    }

    
Gets the value of the specified algorithm parameter. This method
supplies a general-purpose mechanism through which it is possible to
get the various parameters of this object. A parameter may be any
settable parameter for the algorithm, such as a parameter size, or
a source of random bits for signature generation (if appropriate),
or an indication of whether or not to perform a specific but optional
computation. A uniform algorithm-specific naming scheme for each
parameter is desirable but left unspecified at this time.
Params:
param – the string name of the parameter.
Throws:
InvalidParameterException – if param is an invalid parameter for this engine, or another exception occurs while trying to get this parameter.
See Also:
setParameter(String, Object)
Returns:
the object that represents the parameter value, or null if there is none.
Deprecated:
/**
     * Gets the value of the specified algorithm parameter. This method
     * supplies a general-purpose mechanism through which it is possible to
     * get the various parameters of this object. A parameter may be any
     * settable parameter for the algorithm, such as a parameter size, or
     * a source of random bits for signature generation (if appropriate),
     * or an indication of whether or not to perform a specific but optional
     * computation. A uniform algorithm-specific naming scheme for each
     * parameter is desirable but left unspecified at this time.
     *
     * @param param the string name of the parameter.
     *
     * @return the object that represents the parameter value, or {@code null} if
     * there is none.
     *
     * @exception InvalidParameterException if {@code param} is an invalid
     * parameter for this engine, or another exception occurs while
     * trying to get this parameter.
     *
     * @see #setParameter(String, Object)
     *
     * @deprecated
     */
    @Deprecated
    public final Object getParameter(String param)
            throws InvalidParameterException {
        return engineGetParameter(param);
    }

    
Returns a clone if the implementation is cloneable.
Throws:
CloneNotSupportedException – if this is called on an implementation that does not support Cloneable.
Returns:
a clone if the implementation is cloneable./**
     * Returns a clone if the implementation is cloneable.
     *
     * @return a clone if the implementation is cloneable.
     *
     * @exception CloneNotSupportedException if this is called
     * on an implementation that does not support {@code Cloneable}.
     */
    public Object clone() throws CloneNotSupportedException {
        if (this instanceof Cloneable) {
            return super.clone();
        } else {
            throw new CloneNotSupportedException();
        }
    }

    /*
     * The following class allows providers to extend from SignatureSpi
     * rather than from Signature. It represents a Signature with an
     * encapsulated, provider-supplied SPI object (of type SignatureSpi).
     * If the provider implementation is an instance of SignatureSpi, the
     * getInstance() methods above return an instance of this class, with
     * the SPI object encapsulated.
     *
     * Note: All SPI methods from the original Signature class have been
     * moved up the hierarchy into a new class (SignatureSpi), which has
     * been interposed in the hierarchy between the API (Signature)
     * and its original parent (Object).
     */

    @SuppressWarnings("deprecation")
    private static class Delegate extends Signature {

        // The provider implementation (delegate)
        // filled in once the provider is selected
        private SignatureSpi sigSpi;

        // lock for mutex during provider selection
        private final Object lock;

        // next service to try in provider selection
        // null once provider is selected
        private Service firstService;

        // remaining services to try in provider selection
        // null once provider is selected
        private Iterator<Service> serviceIterator;

        // constructor
        Delegate(SignatureSpi sigSpi, String algorithm) {
            super(algorithm);
            this.sigSpi = sigSpi;
            this.lock = null; // no lock needed
        }

        // used with delayed provider selection
        Delegate(Service service,
                        Iterator<Service> iterator, String algorithm) {
            super(algorithm);
            this.firstService = service;
            this.serviceIterator = iterator;
            this.lock = new Object();
        }

        
Returns a clone if the delegate is cloneable.
Throws:
CloneNotSupportedException – if this is called on a delegate that does not support Cloneable.
Returns:
a clone if the delegate is cloneable./**
         * Returns a clone if the delegate is cloneable.
         *
         * @return a clone if the delegate is cloneable.
         *
         * @exception CloneNotSupportedException if this is called on a
         * delegate that does not support {@code Cloneable}.
         */
        public Object clone() throws CloneNotSupportedException {
            chooseFirstProvider();
            if (sigSpi instanceof Cloneable) {
                SignatureSpi sigSpiClone = (SignatureSpi)sigSpi.clone();
                // Because 'algorithm' and 'provider' are private
                // members of our supertype, we must perform a cast to
                // access them.
                Signature that =
                    new Delegate(sigSpiClone, ((Signature)this).algorithm);
                that.provider = ((Signature)this).provider;
                return that;
            } else {
                throw new CloneNotSupportedException();
            }
        }

        private static SignatureSpi newInstance(Service s)
                throws NoSuchAlgorithmException {
            if (s.getType().equals("Cipher")) {
                // must be NONEwithRSA
                try {
                    Cipher c = Cipher.getInstance(RSA_CIPHER, s.getProvider());
                    return new CipherAdapter(c);
                } catch (NoSuchPaddingException e) {
                    throw new NoSuchAlgorithmException(e);
                }
            } else {
                Object o = s.newInstance(null);
                if (o instanceof SignatureSpi == false) {
                    throw new NoSuchAlgorithmException
                        ("Not a SignatureSpi: " + o.getClass().getName());
                }
                return (SignatureSpi)o;
            }
        }

        // max number of debug warnings to print from chooseFirstProvider()
        private static int warnCount = 10;

        
Choose the Spi from the first provider available. Used if
delayed provider selection is not possible because initSign()/
initVerify() is not the first method called.
/**
         * Choose the Spi from the first provider available. Used if
         * delayed provider selection is not possible because initSign()/
         * initVerify() is not the first method called.
         */
        void chooseFirstProvider() {
            if (sigSpi != null) {
                return;
            }
            synchronized (lock) {
                if (sigSpi != null) {
                    return;
                }
                if (debug != null) {
                    int w = --warnCount;
                    if (w >= 0) {
                        debug.println("Signature.init() not first method "
                            + "called, disabling delayed provider selection");
                        if (w == 0) {
                            debug.println("Further warnings of this type will "
                                + "be suppressed");
                        }
                        new Exception("Debug call trace").printStackTrace();
                    }
                }
                Exception lastException = null;
                while ((firstService != null) || serviceIterator.hasNext()) {
                    Service s;
                    if (firstService != null) {
                        s = firstService;
                        firstService = null;
                    } else {
                        s = serviceIterator.next();
                    }
                    if (isSpi(s) == false) {
                        continue;
                    }
                    try {
                        sigSpi = newInstance(s);
                        provider = s.getProvider();
                        // not needed any more
                        firstService = null;
                        serviceIterator = null;
                        return;
                    } catch (NoSuchAlgorithmException e) {
                        lastException = e;
                    }
                }
                ProviderException e = new ProviderException
                        ("Could not construct SignatureSpi instance");
                if (lastException != null) {
                    e.initCause(lastException);
                }
                throw e;
            }
        }

        // Used by engineSetParameter/engineInitSign/engineInitVerify() to
        // find the right provider with the supplied key, parameters, random source
        private void chooseProvider(int type, Key key,
                AlgorithmParameterSpec params, SecureRandom random)
                throws InvalidKeyException, InvalidAlgorithmParameterException {
            synchronized (lock) {
                if (sigSpi != null) {
                    return;
                }
                Exception lastException = null;
                while ((firstService != null) || serviceIterator.hasNext()) {
                    Service s;
                    if (firstService != null) {
                        s = firstService;
                        firstService = null;
                    } else {
                        s = serviceIterator.next();
                    }
                    // if provider says it does not support this key, ignore it
                    if (key != null && s.supportsParameter(key) == false) {
                        continue;
                    }
                    // if instance is not a SignatureSpi, ignore it
                    if (isSpi(s) == false) {
                        continue;
                    }
                    try {
                        SignatureSpi spi = newInstance(s);
                        tryOperation(spi, type, key, params, random);
                        provider = s.getProvider();
                        sigSpi = spi;
                        firstService = null;
                        serviceIterator = null;
                        return;
                    } catch (Exception e) {
                        // NoSuchAlgorithmException from newInstance()
                        // InvalidKeyException from init()
                        // RuntimeException (ProviderException) from init()
                        if (lastException == null) {
                            lastException = e;
                        }
                    }
                }
                // no working provider found, fail
                if (lastException instanceof InvalidKeyException) {
                    throw (InvalidKeyException)lastException;
                }
                if (lastException instanceof RuntimeException) {
                    throw (RuntimeException)lastException;
                }
                if (lastException instanceof InvalidAlgorithmParameterException) {
                    throw (InvalidAlgorithmParameterException)lastException;
                }

                String k = (key != null) ? key.getClass().getName() : "(null)";
                throw new InvalidKeyException
                    ("No installed provider supports this key: "
                    + k, lastException);
            }
        }

        private static final int I_PUB           = 1;
        private static final int I_PRIV          = 2;
        private static final int I_PRIV_SR       = 3;
        private static final int I_PUB_PARAM     = 4;
        private static final int I_PRIV_PARAM_SR = 5;
        private static final int S_PARAM         = 6;

        private void tryOperation(SignatureSpi spi, int type, Key  key,
                AlgorithmParameterSpec params, SecureRandom random)
                throws InvalidKeyException, InvalidAlgorithmParameterException {
            switch (type) {
            case I_PUB:
                spi.engineInitVerify((PublicKey)key);
                break;
            case I_PUB_PARAM:
                spi.engineInitVerify((PublicKey)key, params);
                break;
            case I_PRIV:
                spi.engineInitSign((PrivateKey)key);
                break;
            case I_PRIV_SR:
                spi.engineInitSign((PrivateKey)key, random);
                break;
            case I_PRIV_PARAM_SR:
                spi.engineInitSign((PrivateKey)key, params, random);
                break;
            case S_PARAM:
                spi.engineSetParameter(params);
                break;
            default:
                throw new AssertionError("Internal error: " + type);
            }
        }

        protected void engineInitVerify(PublicKey publicKey)
                throws InvalidKeyException {
            if (sigSpi != null) {
                sigSpi.engineInitVerify(publicKey);
            } else {
                try {
                    chooseProvider(I_PUB, publicKey, null, null);
                } catch (InvalidAlgorithmParameterException iape) {
                    // should not happen, re-throw as IKE just in case
                    throw new InvalidKeyException(iape);
                }
            }
        }

        void engineInitVerify(PublicKey publicKey,
                AlgorithmParameterSpec params)
                throws InvalidKeyException, InvalidAlgorithmParameterException {
            if (sigSpi != null) {
                sigSpi.engineInitVerify(publicKey, params);
            } else {
                chooseProvider(I_PUB_PARAM, publicKey, params, null);
            }
        }

        protected void engineInitSign(PrivateKey privateKey)
                throws InvalidKeyException {
            if (sigSpi != null) {
                sigSpi.engineInitSign(privateKey);
            } else {
                try {
                    chooseProvider(I_PRIV, privateKey, null, null);
                } catch (InvalidAlgorithmParameterException iape) {
                    // should not happen, re-throw as IKE just in case
                    throw new InvalidKeyException(iape);
                }
            }
        }

        protected void engineInitSign(PrivateKey privateKey, SecureRandom sr)
                throws InvalidKeyException {
            if (sigSpi != null) {
                sigSpi.engineInitSign(privateKey, sr);
            } else {
                try {
                    chooseProvider(I_PRIV_SR, privateKey, null, sr);
                } catch (InvalidAlgorithmParameterException iape) {
                    // should not happen, re-throw as IKE just in case
                    throw new InvalidKeyException(iape);
                }
            }
        }

        void engineInitSign(PrivateKey privateKey,
                AlgorithmParameterSpec params, SecureRandom sr)
                throws InvalidKeyException, InvalidAlgorithmParameterException {
            if (sigSpi != null) {
                sigSpi.engineInitSign(privateKey, params, sr);
            } else {
                chooseProvider(I_PRIV_PARAM_SR, privateKey, params, sr);
            }
        }

        protected void engineUpdate(byte b) throws SignatureException {
            chooseFirstProvider();
            sigSpi.engineUpdate(b);
        }

        protected void engineUpdate(byte[] b, int off, int len)
                throws SignatureException {
            chooseFirstProvider();
            sigSpi.engineUpdate(b, off, len);
        }

        protected void engineUpdate(ByteBuffer data) {
            chooseFirstProvider();
            sigSpi.engineUpdate(data);
        }

        protected byte[] engineSign() throws SignatureException {
            chooseFirstProvider();
            return sigSpi.engineSign();
        }

        protected int engineSign(byte[] outbuf, int offset, int len)
                throws SignatureException {
            chooseFirstProvider();
            return sigSpi.engineSign(outbuf, offset, len);
        }

        protected boolean engineVerify(byte[] sigBytes)
                throws SignatureException {
            chooseFirstProvider();
            return sigSpi.engineVerify(sigBytes);
        }

        protected boolean engineVerify(byte[] sigBytes, int offset, int length)
                throws SignatureException {
            chooseFirstProvider();
            return sigSpi.engineVerify(sigBytes, offset, length);
        }

        protected void engineSetParameter(String param, Object value)
                throws InvalidParameterException {
            chooseFirstProvider();
            sigSpi.engineSetParameter(param, value);
        }

        protected void engineSetParameter(AlgorithmParameterSpec params)
                throws InvalidAlgorithmParameterException {
            if (sigSpi != null) {
                sigSpi.engineSetParameter(params);
            } else {
                try {
                    chooseProvider(S_PARAM, null, params, null);
                } catch (InvalidKeyException ike) {
                    // should never happen, rethrow just in case
                    throw new InvalidAlgorithmParameterException(ike);
                }
            }
        }

        protected Object engineGetParameter(String param)
                throws InvalidParameterException {
            chooseFirstProvider();
            return sigSpi.engineGetParameter(param);
        }

        protected AlgorithmParameters engineGetParameters() {
            chooseFirstProvider();
            return sigSpi.engineGetParameters();
        }
    }

    // adapter for RSA/ECB/PKCS1Padding ciphers
    @SuppressWarnings("deprecation")
    private static class CipherAdapter extends SignatureSpi {

        private final Cipher cipher;

        private ByteArrayOutputStream data;

        CipherAdapter(Cipher cipher) {
            this.cipher = cipher;
        }

        protected void engineInitVerify(PublicKey publicKey)
                throws InvalidKeyException {
            cipher.init(Cipher.DECRYPT_MODE, publicKey);
            if (data == null) {
                data = new ByteArrayOutputStream(128);
            } else {
                data.reset();
            }
        }

        protected void engineInitSign(PrivateKey privateKey)
                throws InvalidKeyException {
            cipher.init(Cipher.ENCRYPT_MODE, privateKey);
            data = null;
        }

        protected void engineInitSign(PrivateKey privateKey,
                SecureRandom random) throws InvalidKeyException {
            cipher.init(Cipher.ENCRYPT_MODE, privateKey, random);
            data = null;
        }

        protected void engineUpdate(byte b) throws SignatureException {
            engineUpdate(new byte[] {b}, 0, 1);
        }

        protected void engineUpdate(byte[] b, int off, int len)
                throws SignatureException {
            if (data != null) {
                data.write(b, off, len);
                return;
            }
            byte[] out = cipher.update(b, off, len);
            if ((out != null) && (out.length != 0)) {
                throw new SignatureException
                    ("Cipher unexpectedly returned data");
            }
        }

        protected byte[] engineSign() throws SignatureException {
            try {
                return cipher.doFinal();
            } catch (IllegalBlockSizeException e) {
                throw new SignatureException("doFinal() failed", e);
            } catch (BadPaddingException e) {
                throw new SignatureException("doFinal() failed", e);
            }
        }

        protected boolean engineVerify(byte[] sigBytes)
                throws SignatureException {
            try {
                byte[] out = cipher.doFinal(sigBytes);
                byte[] dataBytes = data.toByteArray();
                data.reset();
                return MessageDigest.isEqual(out, dataBytes);
            } catch (BadPaddingException e) {
                // e.g. wrong public key used
                // return false rather than throwing exception
                return false;
            } catch (IllegalBlockSizeException e) {
                throw new SignatureException("doFinal() failed", e);
            }
        }

        protected void engineSetParameter(String param, Object value)
                throws InvalidParameterException {
            throw new InvalidParameterException("Parameters not supported");
        }

        protected Object engineGetParameter(String param)
                throws InvalidParameterException {
            throw new InvalidParameterException("Parameters not supported");
        }

    }

}