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Java(TM) 2 Platform, Standard Edition, v1.2.2 API Specification: Class X509Certificate - JDK 5 Documentation v1.2.2, Java 2 SDK 英文文档

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java.security.cert
Class X509Certificate

java.lang.Object
  |
  +--java.security.cert.Certificate
        |
        +--java.security.cert.X509Certificate
public abstract class X509Certificate
extends Certificate
implements X509Extension

Abstract class for X.509 certificates. This provides a standard way to access all the attributes of an X.509 certificate.

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: 

 Certificate  ::=  SEQUENCE  {
     tbsCertificate       TBSCertificate,
     signatureAlgorithm   AlgorithmIdentifier,
     signature            BIT STRING  }

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).

These certificates are managed and vouched for by Certificate Authorities (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.

A good decription and profiling is provided in the IETF PKIX WG draft, Part I: X.509 Certificate and CRL Profile, <draft-ietf-pkix-ipki-part1-07.txt>.

The ASN.1 definition of tbsCertificate is: 

 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
     }

Certificates are instantiated using a certificate factory. The following is an example of how to instantiate an X.509 certificate: 

 
 InputStream inStream = new FileInputStream("fileName-of-cert");
 CertificateFactory cf = CertificateFactory.getInstance("X.509");
 X509Certificate cert = (X509Certificate)cf.generateCertificate(inStream);
 inStream.close();

See Also:
Certificate, CertificateFactory, X509Extension

Constructor Summary
protected X509Certificate()
          Constructor for X.509 certificates.
 
Method Summary
abstract  void checkValidity()
          Checks that the certificate is currently valid.
abstract  void checkValidity(Date date)
          Checks that the given date is within the certificate's validity period.
abstract  int getBasicConstraints()
          Gets the certificate constraints path length from the critical BasicConstraints extension, (OID = 2.5.29.19).
abstract  Principal getIssuerDN()
          Gets the issuer (issuer distinguished name) value from the certificate.
abstract  boolean[] getIssuerUniqueID()
          Gets the issuerUniqueID value from the certificate.
abstract  boolean[] getKeyUsage()
          Gets a boolean array representing bits of the KeyUsage extension, (OID = 2.5.29.15).
abstract  Date getNotAfter()
          Gets the notAfter date from the validity period of the certificate.
abstract  Date getNotBefore()
          Gets the notBefore date from the validity period of the certificate.
abstract  BigInteger getSerialNumber()
          Gets the serialNumber value from the certificate.
abstract  String getSigAlgName()
          Gets the signature algorithm name for the certificate signature algorithm.
abstract  String getSigAlgOID()
          Gets the signature algorithm OID string from the certificate.
abstract  byte[] getSigAlgParams()
          Gets the DER-encoded signature algorithm parameters from this certificate's signature algorithm.
abstract  byte[] getSignature()
          Gets the signature value (the raw signature bits) from the certificate.
abstract  Principal getSubjectDN()
          Gets the subject (subject distinguished name) value from the certificate.
abstract  boolean[] getSubjectUniqueID()
          Gets the subjectUniqueID value from the certificate.
abstract  byte[] getTBSCertificate()
          Gets the DER-encoded certificate information, the tbsCertificate from this certificate.
abstract  int getVersion()
          Gets the version (version number) value from the certificate.
 
Methods inherited from class java.security.cert.Certificate
equals, getEncoded, getPublicKey, getType, hashCode, toString, verify, verify
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
 

Constructor Detail

X509Certificate

protected X509Certificate()
Constructor for X.509 certificates.
Method Detail

checkValidity

public abstract void checkValidity()
                            throws CertificateExpiredException,
                                   CertificateNotYetValidException
Checks that the certificate is currently valid. It is if the current date and time are within the validity period given in the certificate.

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: 

 validity             Validity

 Validity ::= SEQUENCE {
     notBefore      CertificateValidityDate,
     notAfter       CertificateValidityDate }

 CertificateValidityDate ::= CHOICE {
     utcTime        UTCTime,
     generalTime    GeneralizedTime }
Throws:
CertificateExpiredException - if the certificate has expired.
CertificateNotYetValidException - if the certificate is not yet valid.

checkValidity

public abstract void checkValidity(Date date)
                            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.
Parameters:
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 date supplied.
CertificateNotYetValidException - if the certificate is not yet valid with respect to the date supplied.
See Also:
checkValidity()

getVersion

public abstract int getVersion()
Gets the version (version number) value from the certificate. The ASN.1 definition for this is: 
 version  [0] EXPLICIT Version DEFAULT v1

 Version ::=  INTEGER  {  v1(0), v2(1), v3(2)  }
Returns:
the version number, i.e. 1, 2 or 3.

getSerialNumber

public abstract BigInteger getSerialNumber()
Gets the 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: 
 serialNumber     CertificateSerialNumber

 
 CertificateSerialNumber  ::=  INTEGER
Returns:
the serial number.

getIssuerDN

public abstract Principal getIssuerDN()
Gets the issuer (issuer distinguished name) value from the certificate. The issuer name identifies the entity that signed (and issued) the certificate.

The issuer name field contains an X.500 distinguished name (DN). The ASN.1 definition for this is: 

 issuer    Name


 Name ::= CHOICE { RDNSequence }
 RDNSequence ::= SEQUENCE OF RelativeDistinguishedName
 RelativeDistinguishedName ::=
     SET OF AttributeValueAssertion

 AttributeValueAssertion ::= SEQUENCE {
                               AttributeType,
                               AttributeValue }
 AttributeType ::= OBJECT IDENTIFIER
 AttributeValue ::= ANY
The Name describes a hierarchical name composed of attributes, such as country name, and corresponding values, such as US. The type of the AttributeValue component is determined by the AttributeType; in general it will be a directoryString. A directoryString is usually one of PrintableString, TeletexString or UniversalString.
Returns:
a Principal whose name is the issuer distinguished name.

getSubjectDN

public abstract Principal getSubjectDN()
Gets the subject (subject distinguished name) value from the certificate. The ASN.1 definition for this is: 
 subject    Name

See getIssuerDN()#getIssuerDN for Name and other relevant definitions.

Returns:
a Principal whose name is the subject name.

getNotBefore

public abstract Date getNotBefore()
Gets the notBefore date from the validity period of the certificate. The relevant ASN.1 definitions are: 
 validity             Validity

 
 Validity ::= SEQUENCE {
     notBefore      CertificateValidityDate,
     notAfter       CertificateValidityDate }

 CertificateValidityDate ::= CHOICE {
     utcTime        UTCTime,
     generalTime    GeneralizedTime }
Returns:
the start date of the validity period.
See Also:
checkValidity()

getNotAfter

public abstract Date getNotAfter()
Gets the notAfter date from the validity period of the certificate. See getNotBefore()#getNotBefore for relevant ASN.1 definitions.
Returns:
the end date of the validity period.
See Also:
checkValidity()

getTBSCertificate

public abstract byte[] getTBSCertificate()
                                  throws CertificateEncodingException
Gets the DER-encoded certificate information, the tbsCertificate from this certificate. This can be used to verify the signature independently.
Returns:
the DER-encoded certificate information.
Throws:
CertificateEncodingException - if an encoding error occurs.

getSignature

public abstract byte[] getSignature()
Gets the signature value (the raw signature bits) from the certificate. The ASN.1 definition for this is: 
 signature     BIT STRING
Returns:
the signature.

getSigAlgName

public abstract String getSigAlgName()
Gets the signature algorithm name for the certificate signature algorithm. An example is the string "SHA-1/DSA". The ASN.1 definition for this is: 
 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

The algorithm name is determined from the algorithm OID string.

Returns:
the signature algorithm name.

getSigAlgOID

public abstract String getSigAlgOID()
Gets the signature algorithm OID string from the certificate. An OID is represented by a set of positive whole numbers separated by periods. For example, the string "1.2.840.10040.4.3" identifies the SHA-1 with DSA signature algorithm, as per the PKIX part I.

See getSigAlgName()#getSigAlgName for relevant ASN.1 definitions.

Returns:
the signature algorithm OID string.

getSigAlgParams

public abstract byte[] getSigAlgParams()
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 AlgorithmParameters.AlgorithmParameters(java.security.AlgorithmParametersSpi, java.security.Provider, java.lang.String) and instantiate with the name returned by getSigAlgName()#getSigAlgName.

See getSigAlgName()#getSigAlgName for relevant ASN.1 definitions.

Returns:
the DER-encoded signature algorithm parameters, or null if no parameters are present.

getIssuerUniqueID

public abstract boolean[] getIssuerUniqueID()
Gets the 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. The PKIX Part I 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.

The ASN.1 definition for this is: 

 issuerUniqueID  [1]  IMPLICIT UniqueIdentifier OPTIONAL

 UniqueIdentifier  ::=  BIT STRING
Returns:
the issuer unique identifier or null if it is not present in the certificate.

getSubjectUniqueID

public abstract boolean[] getSubjectUniqueID()
Gets the subjectUniqueID value from the certificate.

The ASN.1 definition for this is: 

 subjectUniqueID  [2]  IMPLICIT UniqueIdentifier OPTIONAL

 UniqueIdentifier  ::=  BIT STRING
Returns:
the subject unique identifier or null if it is not present in the certificate.

getKeyUsage

public abstract boolean[] getKeyUsage()
Gets a boolean array representing bits of the 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: 
 KeyUsage ::= BIT STRING {
     digitalSignature        (0),
     nonRepudiation          (1),
     keyEncipherment         (2),
     dataEncipherment        (3),
     keyAgreement            (4),
     keyCertSign             (5),
     cRLSign                 (6),
     encipherOnly            (7),
     decipherOnly            (8) }
The PKIX part I draft recommends that when used, this be marked as a critical extension.
Returns:
the bit values of the KeyUsage extension as an array of booleans, or null if the KeyUsage extension is not present in the certificate.

getBasicConstraints

public abstract int getBasicConstraints()
Gets the certificate constraints path length from the critical BasicConstraints extension, (OID = 2.5.29.19).

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 pathLenConstraint field (see below) is meaningful only if 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.

Note that for the PKIX profile this extension is always marked critical if cA is TRUE, meaning this certificate belongs to a Certificate Authority.

The ASN.1 definition for this is: 

 BasicConstraints ::= SEQUENCE {
     cA                  BOOLEAN DEFAULT FALSE,
     pathLenConstraint   INTEGER (0..MAX) OPTIONAL }
Returns:
the length of the constraint if the BasicConstraints extension is present in the certificate and the cA value is TRUE. Otherwise returns -1.
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