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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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
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 * 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 *
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package java.security.cert;

import sun.security.util.SignatureUtil;
import sun.security.x509.X509CertImpl;

import javax.security.auth.x500.X500Principal;
import java.math.BigInteger;
import java.security.*;
import java.util.Collection;
import java.util.Date;
import java.util.List;

/**
 * <p>
 * Abstract class for X.509 certificates. This provides a standard
 * way to access all the attributes of an X.509 certificate.
 * <p>
 * In June of 1996, the basic X.509 v3 format was completed by
 * ISO/IEC and ANSI X9, which is described below in ASN.1:
 * <pre>
 * Certificate  ::=  SEQUENCE  {
 *     tbsCertificate       TBSCertificate,
 *     signatureAlgorithm   AlgorithmIdentifier,
 *     signature            BIT STRING  }
 * </pre>
 * <p>
 * These certificates are widely used to support authentication and
 * other functionality in Internet security systems. Common applications
 * include Privacy Enhanced Mail (PEM), Transport Layer Security (SSL),
 * code signing for trusted software distribution, and Secure Electronic
 * Transactions (SET).
 * <p>
 * These certificates are managed and vouched for by <em>Certificate
 * Authorities</em> (CAs). CAs are services which create certificates by
 * placing data in the X.509 standard format and then digitally signing
 * that data. CAs act as trusted third parties, making introductions
 * between principals who have no direct knowledge of each other.
 * CA certificates are either signed by themselves, or by some other
 * CA such as a "root" CA.
 * <p>
 * More information can be found in
 * <a href="https://tools.ietf.org/html/rfc5280">RFC 5280: Internet X.509
 * Public Key Infrastructure Certificate and CRL Profile</a>.
 * <p>
 * The ASN.1 definition of {@code tbsCertificate} is:
 * <pre>
 * TBSCertificate  ::=  SEQUENCE  {
 *     version         [0]  EXPLICIT Version DEFAULT v1,
 *     serialNumber         CertificateSerialNumber,
 *     signature            AlgorithmIdentifier,
 *     issuer               Name,
 *     validity             Validity,
 *     subject              Name,
 *     subjectPublicKeyInfo SubjectPublicKeyInfo,
 *     issuerUniqueID  [1]  IMPLICIT UniqueIdentifier OPTIONAL,
 *                          -- If present, version must be v2 or v3
 *     subjectUniqueID [2]  IMPLICIT UniqueIdentifier OPTIONAL,
 *                          -- If present, version must be v2 or v3
 *     extensions      [3]  EXPLICIT Extensions OPTIONAL
 *                          -- If present, version must be v3
 *     }
 * </pre>
 * <p>
 * Certificates are instantiated using a certificate factory. The following is
 * an example of how to instantiate an X.509 certificate:
 * <pre>
 * try (InputStream inStream = new FileInputStream("fileName-of-cert")) {
 *     CertificateFactory cf = CertificateFactory.getInstance("X.509");
 *     X509Certificate cert = (X509Certificate)cf.generateCertificate(inStream);
 * }
 * </pre>
 *
 * @author Hemma Prafullchandra
 * @since 1.2
 *
 *
 * @see Certificate
 * @see CertificateFactory
 * @see X509Extension
 */

public abstract class X509Certificate extends Certificate
implements X509Extension {

    @java.io.Serial
    private static final long serialVersionUID = -2491127588187038216L;

    private transient X500Principal subjectX500Principal, issuerX500Principal;

    /**
     * Constructor for X.509 certificates.
     */
    protected X509Certificate() {
        super("X.509");
    }

    /**
     * Checks that the certificate is currently valid. It is if
     * the current date and time are within the validity period given in the
     * certificate.
     * <p>
     * The validity period consists of two date/time values:
     * the first and last dates (and times) on which the certificate
     * is valid. It is defined in
     * ASN.1 as:
     * <pre>
     * validity             Validity
     *
     * Validity ::= SEQUENCE {
     *     notBefore      CertificateValidityDate,
     *     notAfter       CertificateValidityDate }
     *
     * CertificateValidityDate ::= CHOICE {
     *     utcTime        UTCTime,
     *     generalTime    GeneralizedTime }
     * </pre>
     *
     * @throws    CertificateExpiredException if the certificate has expired.
     * @throws    CertificateNotYetValidException if the certificate is not
     * yet valid.
     */
    public abstract void checkValidity()
        throws CertificateExpiredException, CertificateNotYetValidException;

    /**
     * Checks that the given date is within the certificate's
     * validity period. In other words, this determines whether the
     * certificate would be valid at the given date/time.
     *
     * @param date the Date to check against to see if this certificate
     *        is valid at that date/time.
     *
     * @throws    CertificateExpiredException if the certificate has expired
     * with respect to the {@code date} supplied.
     * @throws    CertificateNotYetValidException if the certificate is not
     * yet valid with respect to the {@code date} supplied.
     *
     * @see #checkValidity()
     */
    public abstract void checkValidity(Date date)
        throws CertificateExpiredException, CertificateNotYetValidException;

    /**
     * Gets the {@code version} (version number) value from the
     * certificate.
     * The ASN.1 definition for this is:
     * <pre>
     * version  [0] EXPLICIT Version DEFAULT v1
     *
     * Version ::=  INTEGER  {  v1(0), v2(1), v3(2)  }
     * </pre>
     * @return the version number, i.e. 1, 2 or 3.
     */
    public abstract int getVersion();

    /**
     * Gets the {@code serialNumber} value from the certificate.
     * The serial number is an integer assigned by the certification
     * authority to each certificate. It must be unique for each
     * certificate issued by a given CA (i.e., the issuer name and
     * serial number identify a unique certificate).
     * The ASN.1 definition for this is:
     * <pre>
     * serialNumber     CertificateSerialNumber
     *
     * CertificateSerialNumber  ::=  INTEGER
     * </pre>
     *
     * @return the serial number.
     */
    public abstract BigInteger getSerialNumber();

    /**
     * Gets the {@code issuer} (issuer distinguished name) value from
     * the certificate. The issuer name identifies the entity that signed (and
     * issued) the certificate.
     *
     * <p>The issuer name field contains an
     * X.500 distinguished name (DN).
     * The ASN.1 definition for this is:
     * <pre>
     * issuer    Name
     *
     * Name ::= CHOICE { RDNSequence }
     * RDNSequence ::= SEQUENCE OF RelativeDistinguishedName
     * RelativeDistinguishedName ::=
     *     SET OF AttributeValueAssertion
     *
     * AttributeValueAssertion ::= SEQUENCE {
     *                               AttributeType,
     *                               AttributeValue }
     * AttributeType ::= OBJECT IDENTIFIER
     * AttributeValue ::= ANY
     * </pre>
     * The {@code Name} describes a hierarchical name composed of
     * attributes,
     * such as country name, and corresponding values, such as US.
     * The type of the {@code AttributeValue} component is determined by
     * the {@code AttributeType}; in general it will be a
     * {@code directoryString}. A {@code directoryString} is usually
     * one of {@code PrintableString},
     * {@code TeletexString} or {@code UniversalString}.
     *
     * @return a Principal whose name is the issuer distinguished name.
     *
     * @deprecated Use {@link #getIssuerX500Principal} instead. This method
     * returns the {@code issuer} as an implementation specific
     * {@code Principal} object, which should not be relied upon by portable
     * code.
     */
    @Deprecated(since="16")
    public abstract Principal getIssuerDN();

    /**
     * Returns the issuer (issuer distinguished name) value from the
     * certificate as an {@code X500Principal}.
     * <p>
     * It is recommended that subclasses override this method.
     *
     * @return an {@code X500Principal} representing the issuer
     *          distinguished name
     * @since 1.4
     */
    public X500Principal getIssuerX500Principal() {
        if (issuerX500Principal == null) {
            issuerX500Principal = X509CertImpl.getIssuerX500Principal(this);
        }
        return issuerX500Principal;
    }

    /**
     * Gets the {@code subject} (subject distinguished name) value
     * from the certificate.  If the {@code subject} value is empty,
     * then the {@code getName()} method of the returned
     * {@code Principal} object returns an empty string ("").
     *
     * <p> The ASN.1 definition for this is:
     * <pre>
     * subject    Name
     * </pre>
     *
     * <p>See {@link #getIssuerDN() getIssuerDN} for {@code Name}
     * and other relevant definitions.
     *
     * @return a Principal whose name is the subject name.
     *
     * @deprecated Use {@link #getSubjectX500Principal} instead. This method
     * returns the {@code subject} as an implementation specific
     * {@code Principal} object, which should not be relied upon by portable
     * code.
     */
    @Deprecated(since="16")
    public abstract Principal getSubjectDN();

    /**
     * Returns the subject (subject distinguished name) value from the
     * certificate as an {@code X500Principal}.  If the subject value
     * is empty, then the {@code getName()} method of the returned
     * {@code X500Principal} object returns an empty string ("").
     * <p>
     * It is recommended that subclasses override this method.
     *
     * @return an {@code X500Principal} representing the subject
     *          distinguished name
     * @since 1.4
     */
    public X500Principal getSubjectX500Principal() {
        if (subjectX500Principal == null) {
            subjectX500Principal = X509CertImpl.getSubjectX500Principal(this);
        }
        return subjectX500Principal;
    }

    /**
     * Gets the {@code notBefore} date from the validity period of
     * the certificate.
     * The relevant ASN.1 definitions are:
     * <pre>
     * validity             Validity
     *
     * Validity ::= SEQUENCE {
     *     notBefore      CertificateValidityDate,
     *     notAfter       CertificateValidityDate }
     *
     * CertificateValidityDate ::= CHOICE {
     *     utcTime        UTCTime,
     *     generalTime    GeneralizedTime }
     * </pre>
     *
     * @return the start date of the validity period.
     * @see #checkValidity
     */
    public abstract Date getNotBefore();

    /**
     * Gets the {@code notAfter} date from the validity period of
     * the certificate. See {@link #getNotBefore() getNotBefore}
     * for relevant ASN.1 definitions.
     *
     * @return the end date of the validity period.
     * @see #checkValidity
     */
    public abstract Date getNotAfter();

    /**
     * Gets the DER-encoded certificate information, the
     * {@code tbsCertificate} from this certificate.
     * This can be used to verify the signature independently.
     *
     * @return the DER-encoded certificate information.
     * @throws    CertificateEncodingException if an encoding error occurs.
     */
    public abstract byte[] getTBSCertificate()
        throws CertificateEncodingException;

    /**
     * Gets the {@code signature} value (the raw signature bits) from
     * the certificate.
     * The ASN.1 definition for this is:
     * <pre>
     * signature     BIT STRING
     * </pre>
     *
     * @return the signature.
     */
    public abstract byte[] getSignature();

    /**
     * Gets the signature algorithm name for the certificate
     * signature algorithm. An example is the string "SHA256withRSA".
     * The ASN.1 definition for this is:
     * <pre>
     * signatureAlgorithm   AlgorithmIdentifier
     *
     * AlgorithmIdentifier  ::=  SEQUENCE  {
     *     algorithm               OBJECT IDENTIFIER,
     *     parameters              ANY DEFINED BY algorithm OPTIONAL  }
     *                             -- contains a value of the type
     *                             -- registered for use with the
     *                             -- algorithm object identifier value
     * </pre>
     *
     * <p>The algorithm name is determined from the {@code algorithm}
     * OID string.
     *
     * @return the signature algorithm name.
     */
    public abstract String getSigAlgName();

    /**
     * Gets the signature algorithm OID string from the certificate.
     * An OID is represented by a set of nonnegative whole numbers separated
     * by periods.
     * For example, the string "1.2.840.10040.4.3" identifies the SHA-1
     * with DSA signature algorithm defined in
     * <a href="http://www.ietf.org/rfc/rfc3279.txt">RFC 3279: Algorithms and
     * Identifiers for the Internet X.509 Public Key Infrastructure Certificate
     * and CRL Profile</a>.
     *
     * <p>See {@link #getSigAlgName() getSigAlgName} for
     * relevant ASN.1 definitions.
     *
     * @return the signature algorithm OID string.
     */
    public abstract String getSigAlgOID();

    /**
     * Gets the DER-encoded signature algorithm parameters from this
     * certificate's signature algorithm. In most cases, the signature
     * algorithm parameters are null; the parameters are usually
     * supplied with the certificate's public key.
     * If access to individual parameter values is needed then use
     * {@link java.security.AlgorithmParameters AlgorithmParameters}
     * and instantiate with the name returned by
     * {@link #getSigAlgName() getSigAlgName}.
     *
     * <p>See {@link #getSigAlgName() getSigAlgName} for
     * relevant ASN.1 definitions.
     *
     * @return the DER-encoded signature algorithm parameters, or
     *         null if no parameters are present.
     */
    public abstract byte[] getSigAlgParams();

    /**
     * Gets the {@code issuerUniqueID} value from the certificate.
     * The issuer unique identifier is present in the certificate
     * to handle the possibility of reuse of issuer names over time.
     * RFC 5280 recommends that names not be reused and that
     * conforming certificates not make use of unique identifiers.
     * Applications conforming to that profile should be capable of
     * parsing unique identifiers and making comparisons.
     *
     * <p>The ASN.1 definition for this is:
     * <pre>
     * issuerUniqueID  [1]  IMPLICIT UniqueIdentifier OPTIONAL
     *
     * UniqueIdentifier  ::=  BIT STRING
     * </pre>
     *
     * @return the issuer unique identifier or null if it is not
     * present in the certificate.
     */
    public abstract boolean[] getIssuerUniqueID();

    /**
     * Gets the {@code subjectUniqueID} value from the certificate.
     *
     * <p>The ASN.1 definition for this is:
     * <pre>
     * subjectUniqueID  [2]  IMPLICIT UniqueIdentifier OPTIONAL
     *
     * UniqueIdentifier  ::=  BIT STRING
     * </pre>
     *
     * @return the subject unique identifier or null if it is not
     * present in the certificate.
     */
    public abstract boolean[] getSubjectUniqueID();

    /**
     * Gets a boolean array representing bits of
     * the {@code KeyUsage} extension, (OID = 2.5.29.15).
     * The key usage extension defines the purpose (e.g., encipherment,
     * signature, certificate signing) of the key contained in the
     * certificate.
     * The ASN.1 definition for this is:
     * <pre>
     * KeyUsage ::= BIT STRING {
     *     digitalSignature        (0),
     *     nonRepudiation          (1),
     *     keyEncipherment         (2),
     *     dataEncipherment        (3),
     *     keyAgreement            (4),
     *     keyCertSign             (5),
     *     cRLSign                 (6),
     *     encipherOnly            (7),
     *     decipherOnly            (8) }
     * </pre>
     * RFC 5280 recommends that when used, this be marked
     * as a critical extension.
     *
     * @return the KeyUsage extension of this certificate, represented as
     * an array of booleans. The order of KeyUsage values in the array is
     * the same as in the above ASN.1 definition. The array will contain a
     * value for each KeyUsage defined above. If the KeyUsage list encoded
     * in the certificate is longer than the above list, it will not be
     * truncated. Returns null if this certificate does not
     * contain a KeyUsage extension.
     */
    public abstract boolean[] getKeyUsage();

    /**
     * Gets an unmodifiable list of Strings representing the OBJECT
     * IDENTIFIERs of the {@code ExtKeyUsageSyntax} field of the
     * extended key usage extension, (OID = 2.5.29.37).  It indicates
     * one or more purposes for which the certified public key may be
     * used, in addition to or in place of the basic purposes
     * indicated in the key usage extension field.  The ASN.1
     * definition for this is:
     * <pre>
     * ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX) OF KeyPurposeId
     *
     * KeyPurposeId ::= OBJECT IDENTIFIER
     * </pre>
     *
     * Key purposes may be defined by any organization with a
     * need. Object identifiers used to identify key purposes shall be
     * assigned in accordance with IANA or ITU-T Rec. X.660 |
     * ISO/IEC/ITU 9834-1.
     * <p>
     * This method was added to version 1.4 of the Java 2 Platform Standard
     * Edition. In order to maintain backwards compatibility with existing
     * service providers, this method is not {@code abstract}
     * and it provides a default implementation. Subclasses
     * should override this method with a correct implementation.
     *
     * @return the ExtendedKeyUsage extension of this certificate,
     *         as an unmodifiable list of object identifiers represented
     *         as Strings. Returns null if this certificate does not
     *         contain an ExtendedKeyUsage extension.
     * @throws CertificateParsingException if the extension cannot be decoded
     * @since 1.4
     */
    public List<String> getExtendedKeyUsage() throws CertificateParsingException {
        return X509CertImpl.getExtendedKeyUsage(this);
    }

    /**
     * Gets the certificate constraints path length from the
     * critical {@code BasicConstraints} extension, (OID = 2.5.29.19).
     * <p>
     * The basic constraints extension identifies whether the subject
     * of the certificate is a Certificate Authority (CA) and
     * how deep a certification path may exist through that CA. The
     * {@code pathLenConstraint} field (see below) is meaningful
     * only if {@code cA} is set to TRUE. In this case, it gives the
     * maximum number of CA certificates that may follow this certificate in a
     * certification path. A value of zero indicates that only an end-entity
     * certificate may follow in the path.
     * <p>
     * The ASN.1 definition for this is:
     * <pre>
     * BasicConstraints ::= SEQUENCE {
     *     cA                  BOOLEAN DEFAULT FALSE,
     *     pathLenConstraint   INTEGER (0..MAX) OPTIONAL }
     * </pre>
     *
     * @return the value of {@code pathLenConstraint} if the
     * BasicConstraints extension is present in the certificate and the
     * subject of the certificate is a CA, otherwise -1.
     * If the subject of the certificate is a CA and
     * {@code pathLenConstraint} does not appear,
     * {@code Integer.MAX_VALUE} is returned to indicate that there is no
     * limit to the allowed length of the certification path.
     */
    public abstract int getBasicConstraints();

    /**
     * Gets an immutable collection of subject alternative names from the
     * {@code SubjectAltName} extension, (OID = 2.5.29.17).
     * <p>
     * The ASN.1 definition of the {@code SubjectAltName} extension is:
     * <pre>
     * SubjectAltName ::= GeneralNames
     *
     * GeneralNames :: = SEQUENCE SIZE (1..MAX) OF GeneralName
     *
     * GeneralName ::= CHOICE {
     *      otherName                       [0]     OtherName,
     *      rfc822Name                      [1]     IA5String,
     *      dNSName                         [2]     IA5String,
     *      x400Address                     [3]     ORAddress,
     *      directoryName                   [4]     Name,
     *      ediPartyName                    [5]     EDIPartyName,
     *      uniformResourceIdentifier       [6]     IA5String,
     *      iPAddress                       [7]     OCTET STRING,
     *      registeredID                    [8]     OBJECT IDENTIFIER}
     *
     * OtherName ::= SEQUENCE {
     *      type-id    OBJECT IDENTIFIER,
     *      value      [0] EXPLICIT ANY DEFINED BY type-id }
     * </pre>
     * <p>
     * If this certificate does not contain a {@code SubjectAltName}
     * extension, {@code null} is returned. Otherwise, a
     * {@code Collection} is returned with an entry representing each
     * {@code GeneralName} included in the extension. Each entry is a
     * {@code List} whose first entry is an {@code Integer}
     * (the name type, 0-8) and whose second entry is a {@code String}
     * or a byte array (the name, in string or ASN.1 DER encoded form,
     * respectively). More entries may exist depending on the name type.
     * <p>
     * <a href="http://www.ietf.org/rfc/rfc822.txt">RFC 822</a>, DNS, and URI
     * names are returned as {@code String}s,
     * using the well-established string formats for those types (subject to
     * the restrictions included in RFC 5280). IPv4 address names are
     * returned using dotted quad notation. IPv6 address names are returned
     * in the form "a1:a2:...:a8", where a1-a8 are hexadecimal values
     * representing the eight 16-bit pieces of the address. OID names are
     * returned as {@code String}s represented as a series of nonnegative
     * integers separated by periods. Directory names (distinguished names)
     * are returned in <a href="http://www.ietf.org/rfc/rfc2253.txt">
     * RFC 2253</a> string format. No standard string format is defined for
     * X.400 names or EDI party names. They are returned as byte arrays
     * containing the ASN.1 DER encoded form of the name. otherNames are also
     * returned as byte arrays containing the ASN.1 DER encoded form of the
     * name. A third entry may also be present in the list containing the
     * {@code type-id} of the otherName in string form, and a fourth entry
     * containing its {@code value} as either a string (if the value is
     * a valid supported character string) or a byte array containing the
     * ASN.1 DER encoded form of the value without the context-specific
     * constructed tag with number 0.
     * <p>
     * Note that the {@code Collection} returned may contain more
     * than one name of the same type. Also, note that the returned
     * {@code Collection} is immutable and any entries containing byte
     * arrays are cloned to protect against subsequent modifications.
     * <p>
     * This method was added to version 1.4 of the Java 2 Platform Standard
     * Edition. In order to maintain backwards compatibility with existing
     * service providers, this method is not {@code abstract}
     * and it provides a default implementation. Subclasses
     * should override this method with a correct implementation.
     *
     * @implNote The JDK SUN provider supports the third and fourth
     * otherName entries.
     *
     * @return an immutable {@code Collection} of subject alternative
     * names (or {@code null})
     * @throws CertificateParsingException if the extension cannot be decoded
     * @since 1.4
     */
    public Collection<List<?>> getSubjectAlternativeNames()
        throws CertificateParsingException {
        return X509CertImpl.getSubjectAlternativeNames(this);
    }

    /**
     * Gets an immutable collection of issuer alternative names from the
     * {@code IssuerAltName} extension, (OID = 2.5.29.18).
     * <p>
     * The ASN.1 definition of the {@code IssuerAltName} extension is:
     * <pre>
     * IssuerAltName ::= GeneralNames
     * </pre>
     * The ASN.1 definition of {@code GeneralNames} is defined
     * in {@link #getSubjectAlternativeNames getSubjectAlternativeNames}.
     * <p>
     * If this certificate does not contain an {@code IssuerAltName}
     * extension, {@code null} is returned. Otherwise, a
     * {@code Collection} is returned with an entry representing each
     * {@code GeneralName} included in the extension. Each entry is a
     * {@code List} whose first entry is an {@code Integer}
     * (the name type, 0-8) and whose second entry is a {@code String}
     * or a byte array (the name, in string or ASN.1 DER encoded form,
     * respectively).  More entries may exist depending on the name type.
     * For more details about the formats used for each
     * name type, see the {@code getSubjectAlternativeNames} method.
     * <p>
     * Note that the {@code Collection} returned may contain more
     * than one name of the same type. Also, note that the returned
     * {@code Collection} is immutable and any entries containing byte
     * arrays are cloned to protect against subsequent modifications.
     * <p>
     * This method was added to version 1.4 of the Java 2 Platform Standard
     * Edition. In order to maintain backwards compatibility with existing
     * service providers, this method is not {@code abstract}
     * and it provides a default implementation. Subclasses
     * should override this method with a correct implementation.
     *
     * @return an immutable {@code Collection} of issuer alternative
     * names (or {@code null})
     * @throws CertificateParsingException if the extension cannot be decoded
     * @since 1.4
     */
    public Collection<List<?>> getIssuerAlternativeNames()
        throws CertificateParsingException {
        return X509CertImpl.getIssuerAlternativeNames(this);
    }

    /**
     * Verifies that this certificate was signed using the
     * private key that corresponds to the specified public key.
     * This method uses the signature verification engine
     * supplied by the specified provider. Note that the specified
     * Provider object does not have to be registered in the provider list.
     *
     * This method was added to version 1.8 of the Java Platform Standard
     * Edition. In order to maintain backwards compatibility with existing
     * service providers, this method is not {@code abstract}
     * and it provides a default implementation.
     *
     * @param key the PublicKey used to carry out the verification.
     * @param sigProvider the signature provider.
     *
     * @throws    NoSuchAlgorithmException on unsupported signature
     * algorithms.
     * @throws    InvalidKeyException on incorrect key.
     * @throws    SignatureException on signature errors.
     * @throws    CertificateException on encoding errors.
     * @throws    UnsupportedOperationException if the method is not supported
     * @since 1.8
     */
    public void verify(PublicKey key, Provider sigProvider)
        throws CertificateException, NoSuchAlgorithmException,
        InvalidKeyException, SignatureException {
        String sigName = getSigAlgName();
        Signature sig = (sigProvider == null)
            ? Signature.getInstance(sigName)
            : Signature.getInstance(sigName, sigProvider);

        try {
            SignatureUtil.initVerifyWithParam(sig, key,
                SignatureUtil.getParamSpec(sigName, getSigAlgParams()));
        } catch (ProviderException e) {
            throw new CertificateException(e.getMessage(), e.getCause());
        } catch (InvalidAlgorithmParameterException e) {
            throw new CertificateException(e);
        }

        byte[] tbsCert = getTBSCertificate();
        sig.update(tbsCert, 0, tbsCert.length);

        if (!sig.verify(getSignature())) {
            throw new SignatureException("Signature does not match.");
        }
    }
}
