# java.security.cert

***

**1. Certificate Factory**

```java
CertificateFactory cf = CertificateFactory.getInstance("X.509");
X509Certificate cert = (X509Certificate) cf.generateCertificate(new FileInputStream("cert.der"));
```

**2. Certificate Encodings**

```java
byte[] encoded = cert.getEncoded();
cert = (X509Certificate) CertificateFactory.getInstance("X.509").generateCertificate(new ByteArrayInputStream(encoded));
```

**3. Key Usage**

```java
boolean[] keyUsage = cert.getKeyUsage();
if (keyUsage != null) {
    System.out.println("Key usage: " + Arrays.toString(keyUsage));
}
```

**4. Extended Key Usage**

```java
List<String> extendedKeyUsage = cert.getExtendedKeyUsage();
if (extendedKeyUsage != null) {
    System.out.println("Extended key usage: " + extendedKeyUsage);
}
```

**5. Subject Alternative Names**

```java
List<GeneralName> subjectAltNames = cert.getSubjectAlternativeNames();
if (subjectAltNames != null) {
    System.out.println("Subject alternative names: " + subjectAltNames);
}
```

**6. Issuer and Serial Number**

```java
X500Principal issuer = cert.getIssuerX500Principal();
BigInteger serialNumber = cert.getSerialNumber();
System.out.println("Issuer: " + issuer + ", Serial number: " + serialNumber);
```

**7. Validity Period**

```java
Date notBefore = cert.getNotBefore();
Date notAfter = cert.getNotAfter();
System.out.println("Validity period: " + notBefore + " to " + notAfter);
```

**8. Signature**

```java
byte[] signature = cert.getSignature();
String algorithm = cert.getSigAlgName();
System.out.println("Signature algorithm: " + algorithm + ", Signature: " + Arrays.toString(signature));
```

**9. Public Key**

```java
PublicKey publicKey = cert.getPublicKey();
```

**10. CRL Distribution Points**

```java
List<CRLDistributionPoint> crlDistributionPoints = cert.getCRLDistributionPoints();
if (crlDistributionPoints != null) {
    System.out.println("CRL distribution points: " + crlDistributionPoints);
}
```

**11. Authority Information Access**

```java
List<AuthorityInformationAccess> authorityInfoAccess = cert.getAuthorityInfoAccess();
if (authorityInfoAccess != null) {
    System.out.println("Authority information access: " + authorityInfoAccess);
}
```

**12. Basic Constraints**

```java
boolean ca = cert.getBasicConstraints() != -1;
System.out.println("Certificate authority: " + ca);
```

**13. Trust Anchor**

```java
TrustAnchor trustAnchor = new TrustAnchor(cert, null);
```

**14. Certificate Chain Verification**

```java
CertificateFactory cf = CertificateFactory.getInstance("X.509");
X509Certificate rootCert = (X509Certificate) cf.generateCertificate(new FileInputStream("root.crt"));
X509Certificate intermediateCert = (X509Certificate) cf.generateCertificate(new FileInputStream("intermediate.crt"));
X509Certificate leafCert = (X509Certificate) cf.generateCertificate(new FileInputStream("leaf.crt"));
CertPath certPath = CertPath.getInstance("X.509");
certPath.addCertificate(leafCert);
certPath.addCertificate(intermediateCert);
certPath.addCertificate(rootCert);
PKIXParameters params = new PKIXParameters(Collections.singleton(trustAnchor));
params.setRevocationEnabled(false);
CertPathValidator validator = CertPathValidator.getInstance("PKIX");
PKIXCertPathValidatorResult result = (PKIXCertPathValidatorResult) validator.validate(certPath, params);
```

**15. Certificate Revocation**

```java
CRL crl = CRLFactory.getInstance("PKIX").generateCRL(new FileInputStream("crl.der"));
if (crl.isRevoked(cert)) {
    System.out.println("Certificate has been revoked");
}
```

**16. OCSP Validation**

```java
OCSPClient client = new OCSPClient();
OCSPResp response = client.checkCertStatus(cert, new URL("http://ocsp.example.com"));
if (response.getStatus() == CertificateStatus.GOOD) {
    System.out.println("Certificate is valid");
}
```

**17. HTTPS Client**

```java
URL url = new URL("https://www.example.com");
HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();
X509Certificate[] certs = connection.getServerCertificates();
```

**18. HTTPS Server**

```java
SSLContext sslContext = SSLContext.getInstance("TLS");
KeyManager[] keyManagers = { new KeyManagerImpl() };
TrustManager[] trustManagers = { new TrustManagerImpl() };
sslContext.init(keyManagers, trustManagers, null);
SSLServerSocketFactory factory = sslContext.getServerSocketFactory();
```

**19. LDAP Certificate Retrieval**

```java
LDAPContext ctx = new InitialLdapContext(new Properties(), null);
SearchControls controls = new SearchControls();
controls.setSearchScope(SearchControls.SUBTREE_SCOPE);
NamingEnumeration<SearchResult> results = ctx.search(dn, "(&(objectClass=user)(cn=john))", controls);
byte[] certBytes = results.next().getAttributes().get("userCertificate").get();
```

**20. DNSSEC Validation**

```java
DNSNameResolver resolver = new DNSNameResolver();
resolver.setServerAddress(InetAddress.getByName("dns.example.com"));
List<DNSRecord> records = resolver.lookupRecords(name, DClass.IN, DType.TXT);
```

**21. Certificate Chain Builder**

```java
CertificateFactory cf = CertificateFactory.getInstance("X.509");
X509Certificate intermediateCert = (X509Certificate) cf.generateCertificate(new FileInputStream("intermediate.crt"));
X509Certificate rootCert = (X509Certificate) cf.generateCertificate(new FileInputStream("root.crt"));
CertChainBuilder builder = CertChainBuilder.getInstance("PKIX");
CertPathBuilderResult result = builder.build(new CertPathParameters.Builder(leafCert).addCertPathChecker(new PKIXCertPathChecker()).build());
```

**22. KeyStore**

```java
KeyStore ks = KeyStore.getInstance("JKS");
ks.load(new FileInputStream("keystore.jks"), "password");
```

**23. Certificate Encoding**

```java
byte[] encoded = cert.getEncoded();
```

**24. Certificate Decoding**

```java
CertificateFactory cf = CertificateFactory.getInstance("X.509");
X509Certificate cert = (X509Certificate) cf.generateCertificate(new ByteArrayInputStream(encoded));
```

**25. Certificate Fingerprint**

```java
MessageDigest md = MessageDigest.getInstance("SHA-1");
byte[] fingerprint = md.digest(cert.getEncoded());
```

**26. Certificate Validity Checking**

```java
if (cert.getNotBefore().after(new Date()) || cert.getNotAfter().before(new Date())) {
    System.out.println("Certificate is not valid");
}
```

**27. Certificate Expiration Checking**

```java
Date expirationDate = cert.getNotAfter();
if (expirationDate.before(new Date())) {
    System.out.println("Certificate has expired");
}
```

**28. Certificate Chain Validation**

```java
CertPathBuilder builder = CertPathBuilder.getInstance("PKIX");
CertPathValidator validator = CertPathValidator.getInstance("PKIX");
PKIXParameters params = new PKIXParameters(Collections.singleton(trustAnchor));
CertPathValidationResult result = validator.validate(certPath, params);
```

**29. CRL Retrieval**

```java
CRL crl = CRLFactory.getInstance("PKIX").generateCRL(new URL("http://crl.example.com"));
```

**30. CRL Validation**

```java
if (crl.isRevoked(cert)) {
    System.out.println("Certificate has been revoked");
}
```

**31. OCSP Retrieval**

```java
OCSPClient client = new OCSPClient();
OCSPResp response = client.checkCertStatus(cert, new URL("http://ocsp.example.com"));
```

**32. OCSP Validation**

```java
if (response.getStatus() == CertificateStatus.GOOD) {
    System.out.println("Certificate is valid");
}
```

**33. HTTPS Client with Certificate Validation**

```java
HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();
connection.setHostnameVerifier(new HostnameVerifier() {
    public boolean verify(String hostname, SSLSession session) {
        return session.getPeerCertificates()[0].getSubjectDN().getName().equals("CN=www.example.com");
    }
});
```

**34. HTTPS Server with Certificate Authentication**

```java
SSLContext sslContext = SSLContext.getInstance("TLS");
KeyManager[] keyManagers = { new KeyManagerImpl() };
TrustManager[] trustManagers = { new TrustManagerImpl() };
sslContext.init(keyManagers, trustManagers, null);
SSLServerSocketFactory factory = sslContext.getServerSocketFactory();
```

**35. LDAP Certificate Retrieval**

```java
LDAPContext ctx = new InitialLdapContext(new Properties(), null);
SearchControls controls = new SearchControls();
controls.setSearchScope(SearchControls.SUBTREE_SCOPE);
NamingEnumeration<SearchResult> results = ctx.search(dn, "(&(objectClass=user)(cn=john))", controls);
byte[] certBytes = results.next().getAttributes().get("userCertificate").get();
```

**36. DNSSEC Validation**

```java
DNSNameResolver resolver = new DNSNameResolver();
resolver.setServerAddress(InetAddress.getByName("dns.example.com"));
List<DNSRecord> records = resolver.lookupRecords(name, DClass.IN, DType.TXT);
```

**37. Certificate Encoding**

```java
byte[] encoded = cert.getEncoded();
```

**38. Certificate Decoding**

```java
CertificateFactory cf = CertificateFactory.getInstance("X.509");
X509Certificate cert = (X509Certificate) cf.generateCertificate(new ByteArrayInputStream(encoded));
```

**39. Certificate Fingerprint**

```java
MessageDigest md = MessageDigest.getInstance("SHA-1");
byte[] fingerprint = md.digest(cert.getEncoded());
```

**40. Certificate Validity Checking**

```java
if (cert.getNotBefore().after(new Date()) || cert.getNotAfter().before(new Date())) {
    System.out.println("Certificate is not valid");
}
```

**41. Certificate Expiration Checking**

```java
Date expirationDate = cert.getNotAfter();
if (expirationDate.before(new Date())) {
    System.out.println("Certificate has expired");
}
```

**42. Certificate Chain Validation**

```java
CertPathBuilder builder = CertPathBuilder.getInstance("PKIX");
CertPathValidator validator = CertPathValidator.getInstance("PKIX");
PKIXParameters params = new PKIXParameters(Collections.singleton(trustAnchor));
CertPathValidationResult result = validator.validate(certPath, params);
```

**43. CRL Retrieval**

```java
CRL crl = CRLFactory.getInstance("PKIX").generateCRL(new URL("http://crl.example.com"));
```

**44. CRL Validation**

```java
if (crl.isRevoked(cert)) {
    System.out.println("Certificate has been revoked");
}
```

**45. OCSP Retrieval**

```java
OCSPClient client = new OCSPClient();
OCSPResp response = client.checkCertStatus(cert, new URL("http://ocsp.example.com"));
```

**46. OCSP Validation**

```java
if (response.getStatus() == CertificateStatus.GOOD) {
    System.out.println("Certificate is valid");
}
```

**47. HTTPS Client with Certificate Validation**

```java
HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();
connection.setHostnameVerifier(new HostnameVerifier() {
    public boolean verify(String hostname, SSLSession session) {
        return session.getPeerCertificates()[0].getSubjectDN().getName().equals("CN=www.example.com");
    }
});
```

**48. HTTPS Server with Certificate Authentication**

```java
SSLContext sslContext = SSLContext.getInstance("TLS");
KeyManager[] keyManagers = { new KeyManagerImpl() };
TrustManager[] trustManagers = { new TrustManagerImpl() };
sslContext.init(keyManagers, trustManagers, null);
SSLServerSocketFactory factory = sslContext.getServerSocketFactory();
```

**49. LDAP Certificate Retrieval**

```java
LDAPContext ctx = new InitialLdapContext(new Properties(), null);
SearchControls controls = new SearchControls();
controls.setSearchScope(SearchControls.SUBTREE_SCOPE);
NamingEnumeration<SearchResult> results = ctx.search(dn, "(&(objectClass=user)(cn=john))", controls);
byte[] certBytes = results.next().getAttributes().get("userCertificate").get();
```

**50. DNSSEC Validation**

```java
DNSNameResolver resolver = new DNSNameResolver();
resolver.setServerAddress(InetAddress.getByName("dns.example.com"));
List<DNSRecord> records = resolver.lookupRecords(name, DClass.IN, DType.TXT);
```