JavaTM Cryptography Architecture

API Specification & Reference


Last Modified: 25 July 2004

Introduction
Design Principles
Architecture
Concepts
 
What's New in JCE in the Java 2 Platform Standard Edition 5
 
Core Classes and Interfaces
The Provider Class
How Provider Implementations are Requested and Supplied
Installing Providers
The Security Class
The MessageDigest Class
The Signature Class
Algorithm Parameters Classes
How to Make Applications "Exempt" from Cryptographic Restrictions
Code Examples
Computing a MessageDigest Object
Generating a Pair of Keys
Generating and Verifying a Signature Using Generated Keys
Generating/Verifying Signatures Using Key Specifications and KeyFactory
Determining If Two Keys Are Equal
Reading Base64-Encoded Certificates
Parsing a Certificate Reply
Using Encryption
Using Password-Based Encryption
Using Key Agreement
Appendix A: Standard Names

Appendix B: Algorithms

Appendix C: SunJCE Keysize Restrictions

Appendix D: Jurisdiction Policy File Format

Appendix E: Maximum Key Sizes Allowed by "Strong" Jurisdiction Policy Files

Appendix F: Sample Programs
Diffie-Hellman Key Exchange between 2 Parties
Diffie-Hellman Key Exchange between 3 Parties
Blowfish Example
HMAC-MD5 Example

Introduction

The Security API is a core API of the Java programming language, built around the java.security package (and its subpackages). This API is designed to allow developers to incorporate both low-level and high-level security functionality into their programs.

The first release of Security API in JDK 1.1 introduced the "Java Cryptography Architecture" (JCA), a framework for accessing and developing cryptographic functionality for the Java platform. In JDK 1.1, the JCA included APIs for digital signatures and message digests.

In subsequent releases, the Java 2 SDK significantly extended the Java Cryptography Architecture, as described in this document. It also upgraded the certificate management infrastructure to support X.509 v3 certificates, and introduced a new Java Security Architecture for fine-grain, highly configurable, flexible, and extensible access control.

The Java Cryptography Architecture encompasses the parts of the Java 2 SDK Security API related to cryptography, as well as a set of conventions and specifications provided in this document. It includes a "provider" architecture that allows for multiple and interoperable cryptography implementations.

The JavaTM Cryptography Extension (JCE) provides a framework and implementations for encryption, key generation and key agreement, and Message Authentication Code (MAC) algorithms. Support for encryption includes symmetric, asymmetric, block, and stream ciphers. The software also supports secure streams and sealed objects.

JCE was previously an optional package (extension) to the JavaTM 2 SDK, Standard Edition (Java 2 SDK), versions 1.2.x and 1.3.x. JCE has been integrated into the Java 2 SDK since the 1.4 release.

The JCE API covers:

J2SE 5 comes standard with a JCE provider named "SunJCE", which comes pre-installed and registered and which supplies the following cryptographic services:

A Note on Terminology

The JCE within the JDK includes two software components:

Throughout this document, the term "JCE" by itself refers to the JCE framework in J2SE 5. Whenever the JCE provider supplied with J2SE 5 is mentioned, it will be referred to explicitly as the "SunJCE" provider.
Note: The most recent version of this JCA specification can be found online at: http://java.sun.com/j2se/1.5.0/docs/guide/security/CryptoSpec.html.

Design Principles

The Java Cryptography Architecture (JCA) was designed around these principles:

Implementation independence and algorithm independence are complementary; you can use cryptographic services, such as digital signatures and message digests, without worrying about the implementation details or even the algorithms that form the basis for these concepts. When complete algorithm-independence is not possible, the JCA provides standardized, algorithm-specific APIs. When implementation-independence is not desirable, the JCA lets developers indicate a specific implementation.

Algorithm independence is achieved by defining types of cryptographic "engines" (services), and defining classes that provide the functionality of these cryptographic engines. These classes are called engine classes, and examples are the MessageDigest, Signature, KeyFactory, and KeyPairGenerator classes.

Implementation independence is achieved using a "provider"-based architecture. The term Cryptographic Service Provider (used interchangeably with "provider" in this document) refers to a package or set of packages that implement one or more cryptographic services, such as digital signature algorithms, message digest algorithms, and key conversion services. A program may simply request a particular type of object (such as a Signature object) implementing a particular service (such as the DSA signature algorithm) and get an implementation from one of the installed providers. If desired, a program may instead request an implementation from a specific provider. Providers may be updated transparently to the application, for example when faster or more secure versions are available.

Implementation interoperability means that various implementations can work with each other, use each other's keys, or verify each other's signatures. This would mean, for example, that for the same algorithms, a key generated by one provider would be usable by another, and a signature generated by one provider would be verifiable by another.

Algorithm extensibility means that new algorithms that fit in one of the supported engine classes can be added easily.

Architecture

Cryptographic Service Providers

The Java Cryptography Architecture introduced the notion of a Cryptographic Service Provider (used interchangeably with "provider" in this document). This term refers to a package (or a set of packages) that supplies a concrete implementation of a subset of the cryptography aspects of the Security API.

For example, in JDK 1.1 a provider could contain an implementation of one or more digital signature algorithms, message digest algorithms, and key generation algorithms. Java 2 SDK adds five additional types of services: key factories, keystore creation and management, algorithm parameter management, algorithm parameter generation, and certificate factories. It also enables a provider to supply a random number generation (RNG) algorithm. Previously, RNGs were not provider-based; a particular algorithm was hard-coded in the JDK.

As previously noted, a program may simply request a particular type of object (such as a Signature object) for a particular service (such as the DSA signature algorithm) and get an implementation from one of the installed providers. Alternatively, the program can request the objects from a specific provider. (Each provider has a name used to refer to it.)

Sun's version of the Java runtime environment comes standard with a default provider, named SUN. Other Java runtime environments may not necessarily supply the SUN provider. The SUN provider package includes:

Each SDK installation has one or more provider packages installed. New providers may be added statically or dynamically (see the Provider and Security classes). The Java Cryptography Architecture offers a set of APIs that allow users to query which providers are installed and what services they support.

Clients may configure their runtime with different providers, and specify a preference order for each of them. The preference order is the order in which providers are searched for requested services when no specific provider is requested.

Key Management

A database called a "keystore" can be used to manage a repository of keys and certificates. A keystore is available to applications that need it for authentication or signing purposes.

Applications can access a keystore via an implementation of the KeyStore class, which is in the java.security package. A default KeyStore implementation is provided by Sun Microsystems. It implements the keystore as a file, using a proprietary keystore type (format) named "JKS".

Applications can choose different types of keystore implementations from different providers, using the getInstance factory method supplied in the KeyStore class.

See the Key Management section for more information.

Concepts

This section covers the major concepts introduced in the API.

Engine Classes and Algorithms

An engine class defines a cryptographic service in an abstract fashion (without a concrete implementation).

A cryptographic service is always associated with a particular algorithm or type, and it either provides cryptographic operations (like those for digital signatures or message digests), generates or supplies the cryptographic material (keys or parameters) required for cryptographic operations, or generates data objects (keystores or certificates) that encapsulate cryptographic keys (which can be used in a cryptographic operation) in a secure fashion. For example, two of the engine classes are the Signature and KeyFactory classes. The Signature class provides access to the functionality of a digital signature algorithm. A DSA KeyFactory supplies a DSA private or public key (from its encoding or transparent specification) in a format usable by the initSign or initVerify methods, respectively, of a DSA Signature object.

The Java Cryptography Architecture encompasses the classes of the Java 2 SDK Security package related to cryptography, including the engine classes. Users of the API request and use instances of the engine classes to carry out corresponding operations. The following engine classes are defined in Java 2 SDK:

In the 1.4 release of the Java 2 SDK, the following new engines were added:
Note: A generator creates objects with brand-new contents, whereas a factory creates objects from existing material (for example, an encoding).
An engine class provides the interface to the functionality of a specific type of cryptographic service (independent of a particular cryptographic algorithm). It defines Application Programming Interface (API) methods that allow applications to access the specific type of cryptographic service it provides. The actual implementations (from one or more providers) are those for specific algorithms. The Signature engine class, for example, provides access to the functionality of a digital signature algorithm. The actual implementation supplied in a SignatureSpi subclass would be that for a specific kind of signature algorithm, such as SHA-1 with DSA, SHA-1 with RSA, or MD5 with RSA.

The application interfaces supplied by an engine class are implemented in terms of a Service Provider Interface (SPI). That is, for each engine class, there is a corresponding abstract SPI class, which defines the SPI methods that cryptographic service providers must implement.

An instance of an engine class, the API object, encapsulates (as a private field) an instance of the corresponding SPI class, the SPI object. All API methods of an API object are declared final and their implementations invoke the corresponding SPI methods of the encapsulated SPI object. An instance of an engine class (and of its corresponding SPI class) is created by a call to the getInstance factory method of the engine class.

The name of each SPI class is the same as that of the corresponding engine class, followed by Spi. For example, the SPI class corresponding to the Signature engine class is the SignatureSpi class.

Each SPI class is abstract. To supply the implementation of a particular type of service, for a specific algorithm, a provider must subclass the corresponding SPI class and provide implementations for all the abstract methods.

Another example of an engine class is the MessageDigest class, which provides access to a message digest algorithm. Its implementations, in MessageDigestSpi subclasses, may be those of various message digest algorithms such as SHA-1, MD5, or MD2.

As a final example, the KeyFactory engine class supports the conversion from opaque keys to transparent key specifications, and vice versa. (See the Key Specification Interfaces and Classes section.) The KeyFactorySpi subclass supplies an actual implementation for a specific type of keys, for example, DSA public and private keys.

Implementations and Providers

Implementations for various cryptographic services are provided by JCA Cryptographic Service Providers. Cryptographic service providers are essentially packages that supply one or more cryptographic service implementations. The Engine Classes and Algorithms section includes a list of implemenations supplied by SUN, the Java 2 SDK's default provider.

Other providers may define their own implementations of these services or of other services, such as one of the RSA-based signature algorithms or the MD2 message digest algorithm.

Factory Methods to Obtain Implementation Instances

For each engine class in the API, a particular implementation is requested and instantiated by calling a factory method on the engine class. A factory method is a static method that returns an instance of a class.

The basic mechanism for obtaining an appropriate Signature object, for example, is as follows: A user requests such an object by calling the getInstance method in the Signature class, specifying the name of a signature algorithm (such as "SHA1withDSA"), and, optionally, the name of the provider or the Provider class. The getInstance method finds an implementation that satisfies the supplied algorithm and provider parameters. If no provider is specified, getInstance searches the registered providers, in preference order, for one with an implementation of the specified algorithm. See The Provider Class for more information about registering providers.

Cryptographic Concepts

This section provides a high-level description of the concepts implemented by the API, and the exact meaning of the technical terms used in the API specification.

Encryption and Decryption

Encryption is the process of taking data (called cleartext) and a short string (a key), and producing data (ciphertext) meaningless to a third-party who does not know the key. Decryption is the inverse process: that of taking ciphertext and a short key string, and producing cleartext.

Password-Based Encryption

Password-Based Encryption (PBE) derives an encryption key from a password. In order to make the task of getting from password to key very time-consuming for an attacker, most PBE implementations will mix in a random number, known as a salt, to create the key.

Cipher

Encryption and decryption are done using a cipher. A cipher is an object capable of carrying out encryption and decryption according to an encryption scheme (algorithm).

Key Agreement

Key agreement is a protocol by which 2 or more parties can establish the same cryptographic keys, without having to exchange any secret information.

Message Authentication Code

A Message Authentication Code (MAC) provides a way to check the integrity of information transmitted over or stored in an unreliable medium, based on a secret key. Typically, message authentication codes are used between two parties that share a secret key in order to validate information transmitted between these parties.

A MAC mechanism that is based on cryptographic hash functions is referred to as HMAC. HMAC can be used with any cryptographic hash function, e.g., MD5 or SHA-1, in combination with a secret shared key. HMAC is specified in RFC 2104.

What's New in JCE in J2SE 5

Here are the differences in JCE between v1.4 and J2SE 5:

Support for PKCS #11 Based Crypto Provider

In J2SE 5, a JCA/JCE provider, SunPKCS11 that acts as a generic gateway to the native PKCS#11 API has been implemented. PKCS#11 is the de-facto standard for crypto accelerators and also widely used to access cryptographic smartcards. The administrator/user can configure this provider to talk any PKCS#11 v2.x compliant token.

Here's an example of the configuration file format.

Integration with Solaris Cryptographic Framework

On Solaris 10, the default Java security provider configuration has been changed in J2SE 5 to include an instance of the SunPKCS11 provider that uses the Solaris Cryptographic Framework. It is the provider with the highest precedence thereby allowing all existing applications to take advantage of the improved performance on Solaris 10. There is no change in behavior on Solaris 8 and Solaris 9 systems.

As a result of this change, many cryptographic operations will execute several times as fast as before on all Solaris 10 systems. On systems with cryptographic hardware acceleration, the performance improvements may be two orders of magnitude.

Support for ECC Algorithm

Prior to J2SE 5, the JCA/JCE framework did not include support classes for ECC-related crypto algorithms. Users who wanted to use ECC had to depend on a 3rd party library that implemented ECC. However, this did not integrate well with existing JCA/JCE framework.

Starting in J2SE 5, full support for ECC classes to facilitate providers that support ECC have been included.

The following interfaces have been added:

The following classes have been added:

Added ByteBuffer API Support

Methods that take ByteBuffer arguments have been added to the JCE API and SPI classes that are used to process bulk data. Providers can override the engine* methods if they can process ByteBuffers more efficiently than byte[].

The following JCE methods have been added to support ByteBuffers: 

    javax.crypto.Mac.update(ByteBuffer input)
    javax.crypto.MacSpi.engineUpdate(ByteBuffer input)
    javax.crypto.Cipher.update(ByteBuffer input, ByteBuffer output)
    javax.crypto.Cipher.doFinal(ByteBuffer input, ByteBuffer output)
    javax.crypto.CipherSpi.engineUpdate(ByteBuffer input, ByteBuffer output)
    javax.crypto.CipherSpi.engineDoFinal(ByteBuffer input, ByteBuffer output)
The following JCA methods have been added to support ByteBuffers: 
    java.security.MessageDigest.update(ByteBuffer input)
    java.security.Signature.update(ByteBuffer data)
    java.security.SignatureSpi.engineUpdate(ByteBuffer data)
    java.security.MessageDigestSpi.engineUpdate(ByteBuffer input)

Support for RC2ParameterSpec

The RC2 algorithm implementation has been enhanced in J2SE 5 to support effective key size that is distinct from the length of the input key.

Full support for XML Encryption RSA-OAEP Algorithm

Prior to J2SE 5, JCE did not define any parameter class for specifying the non-default values used in OAEP and PSS padding as defined in PKCS#1 v2.1 and the RSA-OAEP Key Transport algorithm in the W3C Recommendation for XML Encryption. Therefore, there was no generic way for applications to specify non-default values used in OAEP and PSS padding.

In J2SE 5, new parameter classes have been added to fully support OAEP padding and the existing PSS parameter class was enhanced with APIs to fully support RSA PSS signature implementations. Also, SunJCE provider has been enhanced to accept OAEPParameterSpec when OAEPPadding is used.

The following classes have been added:

The following methods and fields have been added to java.security.spec.PSSParameterSpec: 

    public static final PSSParameterSpec DEFAULT
    public PSSParameterSpec(String mdName, String mgfName,
                            AlgorithmParameterSpec mgfSpec,
                            int saltLen, int trailerField)
    public String getDigestAlgorithm()
    public String getMGFAlgorithm()
    public AlgorithmParameterSpec getMGFParameters()
    public int getTrailerField()

Simplified Retrieval of PKCS8EncodedKeySpec from javax.crypto.EncryptedPrivateKeyInfo

In J2SE 5, javax.crypto.EncryptedPrivateKeyInfo only has one method, getKeySpec(Cipher) for retrieving the PKCS8EncodedKeySpec from the encrypted data. This limitation requires users to specify a cipher which is initialized with the decryption key and parameters. When users only have the decryption key, they would have to first retrieve the parameters out of this EncryptedPrivateKeyInfo object, get hold of matching Cipher implementation, initialize it, and then call the getKeySpec(Cipher) method.

To make EncyptedPrivateKeyInfo easier to use and to make its API consistent with javax.crypto.SealedObject, the following methods have been added to javax.crypto.EncryptedPrivateKeyInfo: 

    getKeySpec(Key decryptKey)
    getKeySpec(Key decryptKey, String provider)

Ability to Dynamically Determine Maximum Allowable Key Length

In 1.4.2, the crypto jurisdiction policy files bundled in J2SE limits the maximum key length (and parameter value for some crypto algorithms) that can be used for encryption/decryption. Users who desire unlimited version of crypto jurisdiction files must download them separately.

Also, an exception is thrown when the Cipher instance is initialized with keys (or parameters for certain crypto algorithms) exceeds the maximum values allowed by the crypto jurisdiction files.

In J2SE 5, the Cipher class has been updated to provide the maximum values for key length and parameters configured in the jurisdiction policy files, so that applications can use a shorter key length when the default (limited strength) jurisdiction policy files are installed.

The following methods have been added to javax.crypto.Cipher: 

    public static final int getMaxAllowedKeyLength(String transformation)
             throws NoSuchAlgorithmException

    public static final AlgorithmParameterSpec
             getMaxAllowedParameterSpec(String transformation)
             throws NoSuchAlgorithmException;

Support for HmacSHA256, HmacSHA384, HmacSHA512

Support for HmacSHA-256, HmacSHA-384, and HmacSHA-512 algorithms have been added to J2SE 5.

Support for RSA Encryption to SunJCE Provider

A publicly accessible RSA encryption implementation has been added to the SunJCE provider.

Support for RC2 and ARCFOUR Ciphers to SunJCE Provider

The SunJCE provider now implements the RC2 (RFC 2268) and ARCFOUR (an RC4TM-compatible algorithm) ciphers.

Support for "PBEWithSHA1AndDESede" and "PBEWithSHA1AndRC2_40" Ciphers

Added support for PBEWithSHA1AndDESede and PBEWithSHA1AndRC2_40 ciphers in SunJCE provider.

Support for XML Encryption Padding Algorithm in JCE Block Encryption Ciphers

W3C XML Encryption defines a new padding algorithm, "ISO10126Padding," for block ciphers. See 5.2 Block Encryption Algorithms for more information.

To allow Sun's provider to be used by XML Encryption implementations and JSR 106 providers, we have added support for this padding in J2SE 5.

Core Classes and Interfaces

This section discusses the core classes and interfaces provided in the Java Cryptography Architecture:

engine classes

  • the Key interfaces and classes

  • the Algorithm Parameter Specification Interfaces and Classes and the Key Specification Interfaces and Classes

    This section shows the signatures of the main methods in each class and interface. Examples for some of these classes (MessageDigest, Signature, KeyPairGenerator, SecureRandom, KeyFactory, and key specification classes) are supplied in the corresponding Examples sections. The complete reference documentation for the relevant Security API packages can be found in:

    • The Provider Class

    The term "Cryptographic Service Provider" (used interchangeably with "provider" in this document) refers to a package or set of packages that supply a concrete implementation of a subset of the Java 2 SDK Security API cryptography features. The Provider class is the interface to such a package or set of packages. It has methods for accessing the provider name, version number, and other information. Please note that in addition to registering implementations of cryptographic services, the Provider class can also be used to register implementations of other security services that might get defined as part of the Java 2 SDK Security API or one of its extensions.

    To supply implementations of cryptographic services, an entity (e.g., a development group) writes the implementation code and creates a subclass of the Provider class. The constructor of the Provider subclass sets the values of various properties; the Java 2 SDK Security API uses these values to look up the services that the provider implements. In other words, the subclass specifies the names of the classes implementing the services.

    There are several types of services that can be implemented by provider packages; for more information, see Engine Classes and Algorithms.

    The different implementations may have different characteristics. Some may be software-based, while others may be hardware-based. Some may be platform-independent, while others may be platform-specific. Some provider source code may be available for review and evaluation, while some may not. The Java Cryptography Architecture (JCA) lets both end-users and developers decide what their needs are.

    In this section we explain how end-users install the cryptography implementations that fit their needs, and how developers request the implementations that fit theirs.

    Note: For information about implementing a provider, see the guide How To Implement a Provider for the Java Cryptography Architecture.

    How Provider Implementations Are Requested and Supplied

    For each engine class in the API, a particular implementation is requested and instantiated by calling a getInstance method on the engine class, specifying the name of the desired algorithm and, optionally, the name of the provider (or the Provider class) whose implementation is desired.

    If no provider is specified, getInstance searches the registered providers for an implementation of the requested cryptographic service associated with the named algorithm. In any given Java Virtual Machine (JVM), providers are installed in a given preference order, the order in which the provider list is searched if a specific provider is not requested. For example, suppose there are two providers installed in a JVM, PROVIDER_1 and PROVIDER_2. Assume that:

    Now let's look at three scenarios:
    1. If we are looking for an MD5 implementation. Both providers supply such an implementation. The PROVIDER_1 implementation is returned since PROVIDER_1 has the highest priority and is searched first.
    2. If we are looking for an MD5withRSA signature algorithm, PROVIDER_1 is first searched for it. No implementation is found, so PROVIDER_2 is searched. Since an implementation is found, it is returned.
    3. Suppose we are looking for a SHA1withRSA signature algorithm. Since no installed provider implements it, a NoSuchAlgorithmException is thrown.

    The getInstance methods that include a provider argument are for developers who want to specify which provider they want an algorithm from. A federal agency, for example, will want to use a provider implementation that has received federal certification. Let's assume that the SHA1withDSA implementation from PROVIDER_1 has not received such certification, while the DSA implementation of PROVIDER_2 has received it.

    A federal agency program would then have the following call, specifying PROVIDER_2 since it has the certified implementation: 

    Signature dsa = Signature.getInstance("SHA1withDSA", "PROVIDER_2");

    In this case, if PROVIDER_2 was not installed, a NoSuchProviderException would be thrown, even if another installed provider implements the algorithm requested.

    A program also has the option of getting a list of all the installed providers (using the getProviders method in the Security class) and choosing one from the list.

    Installing Providers

    There are two parts to installing a provider: installing the provider package classes, and configuring the provider.

    Installing the Provider Classes

    There are two possible ways to install the provider classes:

    1. Place a zip or JAR file containing the classes anywhere in your classpath.

    2. Supply your provider JAR file as an "installed" or "bundled" extension. For more information on how to deploy an extension, see How is an extension deployed?.

    Configuring the Provider

    The next step is to add the provider to your list of approved providers. This step can be done statically by editing the java.security file in the lib/security directory of the SDK; therefore, if the SDK is installed in a directory called j2sdk1.2, the file would be j2sdk1.2/lib/security/java.security. One of the types of properties you can set in java.security has the following form: 

    security.provider.n=masterClassName

    This declares a provider, and specifies its preference order n. The preference order is the order in which providers are searched for requested algorithms (when no specific provider is requested). The order is 1-based: 1 is the most preferred, followed by 2, and so on.

    masterClassName must specify the provider's master class. The provider's documentation will specify its master class. This class is always a subclass of the Provider class. The subclass constructor sets the values of various properties that are required for the Java Cryptography API to look up the algorithms or other facilities the provider implements.

    Suppose that the master class is COM.acme.provider.Acme, and that you would like to configure Acme as your third preferred provider. To do so, you would add the following line to the java.security file: 

    security.provider.3=COM.acme.provider.Acme
    Providers may also be registered dynamically. To do so, call either the addProvider or insertProviderAt method in the Security class. This type of registration is not persistent and can only be done by "trusted" programs. See Security.

    Provider Class Methods

    Each Providerclass instance has a (currently case-sensitive) name, a version number, and a string description of the provider and its services. You can query the Provider instance for this information by calling the following methods: 

    public String getName()
public double getVersion()
public String getInfo()

    The Security Class

    The Security class manages installed providers and security-wide properties. It only contains static methods and is never instantiated. The methods for adding or removing providers, and for setting Security properties, can only be executed by a trusted program. Currently, a "trusted program" is either

    The determination that code is considered trusted to perform an attempted action (such as adding a provider) requires that the applet is granted permission for that particular action.

    For example, in the Policy reference implementation, the policy configuration file(s) for a SDK installation specify what permissions (which types of system resource accesses) are allowed by code from specified code sources. (See below and the "Default Policy Implementation and Policy File Syntax" and "Java Security Architecture Specification" files for more information.)

    Code being executed is always considered to come from a particular "code source". The code source includes not only the location (URL) where the applet originated from, but also a reference to the public key(s) corresponding to the private key(s) used to sign the code. Public keys in a code source are referenced by (symbolic) alias names from the user's keystore .

    In a policy configuration file, a code source is represented by two components: a code base (URL), and an alias name (preceded by signedBy), where the alias name identifies the keystore entry containing the public key that must be used to verify the code's signature.

    Each "grant" statement in such a file grants a specified code source a set of permissions, specifying which actions are allowed.

    Here is a sample policy configuration file: 

    grant codeBase "file:/home/sysadmin/", signedBy "sysadmin" {
    permission java.security.SecurityPermission "insertProvider.*";
    permission java.security.SecurityPermission "removeProvider.*";
    permission java.security.SecurityPermission "putProviderProperty.*";
};
    This configuration file specifies that only code loaded from a signed JAR file from beneath the /home/sysadmin/ directory on the local file system can add or remove providers or set provider properties. (Note that the signature of the JAR file can be verified using the public key referenced by the alias name sysadmin in the user's keystore.)

    Either component of the code source (or both) may be missing. Here's an example of a configuration file where codeBase is missing: 

    grant signedBy "sysadmin" {
    permission java.security.SecurityPermission "insertProvider.*";
    permission java.security.SecurityPermission "removeProvider.*";
};
    If this policy is in effect, code that comes in a JAR File signed by sysadmin can add/remove providers--regardless of where the JAR File originated.

    Here's an example without a signer: 

    grant codeBase "file:/home/sysadmin/" {
    permission java.security.SecurityPermission "insertProvider.*";
    permission java.security.SecurityPermission "removeProvider.*";
};
    In this case, code that comes from anywhere within the /home/sysadmin/ directory on the local filesystem can add/remove providers. The code does not need to be signed.

    An example where neither codeBase nor signedBy is included is: 

    grant {
    permission java.security.SecurityPermission "insertProvider.*";
    permission java.security.SecurityPermission "removeProvider.*";
};
    Here, with both code source components missing, any code (regardless of where it originates, or whether or not it is signed, or who signed it) can add/remove providers.

    Managing Providers

    The following tables summarize the methods in the Security class you can use to query which Providers are installed, as well as to install or remove providers at runtime.

    Quering Providers
    Method Description
    static Provider[] getProviders() Returns an array containing all the installed providers (technically, the Provider subclass for each package provider). The order of the Providers in the array is their preference order.
    static Provider getProvider
    (String providerName)    		 Returns the Provider named providerName. It returns null if the Provider is not found.

    Adding Providers
    Method Description 
    static int 
    addProvider(Provider provider)
    		 Adds a Provider to the end of the list of installed Providers. It returns the preference position in which the Provider was added, or -1 if the Provider was not added because it was already installed.
    static int insertProviderAt
    (Provider provider, int position)

    Adds a new Provider at a specified position. If the given provider is installed at the requested position, the provider formerly at that position and all providers with a position greater than position are shifted up one position (towards the end of the list). This method returns the preference position in which the Provider was added, or -1 if the Provider was not added because it was already installed.

    Removing Providers
     Method  Description
    static void removeProvider(String name) Removes the Provider with the specified name. It returns silently if the provider is not installed. When the specified provider is removed, all providers located at a position greater than where the specified provider was are shifted down one position (towards the head of the list of installed providers).

    Note: If you want to change the preference position of a provider, you must first remove it, and then insert it back in at the new preference position.

    Security Properties

    The Security class maintains a list of system-wide security properties. These properties are accessible and settable by a trusted program via the following methods: 

    static String getProperty(String key)
static void setProperty(String key, String datum)

    The MessageDigest Class

    The MessageDigest class is an engine class designed to provide the functionality of cryptographically secure message digests such as SHA-1 or MD5. A cryptographically secure message digest takes arbitrary-sized input (a byte array), and generates a fixed-size output, called a digest or hash. A digest has two properties:

    Message digests are used to produce unique and reliable identifiers of data. They are sometimes called the "digital fingerprints" of data.

    Creating a MessageDigest Object

    The first step for computing a digest is to create a message digest instance. As with all engine classes, the way to get a MessageDigest object for a particular type of message digest algorithm is to call the getInstance static factory method on the MessageDigest class: 

    static MessageDigest getInstance(String algorithm)
    Note: The algorithm name is not case-sensitive. For example, all the following calls are equivalent: 
    MessageDigest.getInstance("SHA-1")
MessageDigest.getInstance("sha-1")
MessageDigest.getInstance("sHa-1")

    A caller may optionally specify the name of a provider or a Provider instance, which guarantees that the implementation of the algorithm requested is from the specified provider: 

    static MessageDigest getInstance(String algorithm, String provider)
static MessageDigest getInstance(String algorithm, Provider provider)

    A call to getInstance returns an initialized message digest object. It thus does not need further initialization.

    Updating a Message Digest Object

    The next step for calculating the digest of some data is to supply the data to the initialized message digest object. This is done by calling one of the update methods: 

    void update(byte input)
void update(byte[] input)
void update(byte[] input, int offset, int len)

    Computing the Digest

    After the data has been supplied by calls to update methods, the digest is computed using a call to one of the digest methods: 

    byte[] digest()
byte[] digest(byte[] input)
int digest(byte[] buf, int offset, int len)

    The first two methods return the computed digest. The latter method stores the computed digest in the provided buffer buf, starting at offset. len is the number of bytes in buf allotted for the digest. The method returns the number of bytes actually stored in buf.

    A call to the digest method that takes an input byte array argument is equivalent to making a call to 

    void update(byte[] input)
    with the specified input, followed by a call to the digest method without any arguments.

    Please see the Examples section for more details.

    The Signature Class

    The Signature class is an engine class designed to provide the functionality of a cryptographic digital signature algorithm such as DSA or RSA with MD5. A cryptographically secure signature algorithm takes arbitrary-sized input and a private key and generates a relatively short (often fixed-size) string of bytes, called the signature, with the following properties:

    A Signature object can be used to sign data. It can also be used to verify whether or not an alleged signature is in fact the authentic signature of the data associated with it. Please see the Examples section for an example of signing and verifying data.

    Signature Object States

    Signature objects are modal objects. This means that a Signature object is always in a given state, where it may only do one type of operation. States are represented as final integer constants defined in their respective classes.

    The three states a Signature object may have are:

    When it is first created, a Signature object is in the UNINITIALIZED state. The Signature class defines two initialization methods, initSign and initVerify, which change the state to SIGN and VERIFY, respectively.

    Creating a Signature Object

    The first step for signing or verifying a signature is to create a Signature instance. As with all engine classes, the way to get a Signature object for a particular type of signature algorithm is to call the getInstance static factory method on the Signature class: 
    static Signature getInstance(String algorithm)
    Note: The algorithm name is not case-sensitive.
    A caller may optionally specify the name of a provider or the Provider class, which will guarantee that the implementation of the algorithm requested is from the named provider: 

    static Signature getInstance(String algorithm, String provider)
static Signature getInstance(String algorithm, Provider provider)

    Initializing a Signature Object

    A Signature object must be initialized before it is used. The initialization method depends on whether the object is going to be used for signing or for verification.

    If it is going to be used for signing, the object must first be initialized with the private key of the entity whose signature is going to be generated. This initialization is done by calling the method: 

    final void initSign(PrivateKey privateKey)
    This method puts the Signature object in the SIGN state.

    If instead the Signature object is going to be used for verification, it must first be initialized with the public key of the entity whose signature is going to be verified. This initialization is done by calling either of these methods: 

        final void initVerify(PublicKey publicKey)

    final void initVerify(Certificate certificate)

    This method puts the Signature object in the VERIFY state.

    Signing

    If the Signature object has been initialized for signing (if it is in the SIGN state), the data to be signed can then be supplied to the object. This is done by making one or more calls to one of the update methods: 

    final void update(byte b)
final void update(byte[] data)
final void update(byte[] data, int off, int len)

    Calls to the update method(s) should be made until all the data to be signed has been supplied to the Signature object.

    To generate the signature, simply call one of the sign methods: 

    final byte[] sign()
final int sign(byte[] outbuf, int offset, int len)

    The first method returns the signature result in a byte array. The second stores the signature result in the provided buffer outbuf, starting at offset. len is the number of bytes in outbuf allotted for the signature. The method returns the number of bytes actually stored.

    Signature encoding is algorithm specific. See Appendix B for more information about the use of ASN.1 encoding in the Java Cryptography Architecture.

    A call to a sign method resets the signature object to the state it was in when previously initialized for signing via a call to initSign. That is, the object is reset and available to generate another signature with the same private key, if desired, via new calls to update and sign.

    Alternatively, a new call can be made to initSign specifying a different private key, or to initVerify (to initialize the Signature object to verify a signature).

    Verifying

    If the Signature object has been initialized for verification (if it is in the VERIFY state), it can then verify if an alleged signature is in fact the authentic signature of the data associated with it. To start the process, the data to be verified (as opposed to the signature itself) is supplied to the object. The data is passed to the object by calling one of the update methods: 

    final void update(byte b)
final void update(byte[] data)
final void update(byte[] data, int off, int len)

    Calls to the update method(s) should be made until all the data to be verified has been supplied to the Signature object. The signature can now be verified by calling one of the verify methods: 

    final boolean verify(byte[] signature)

final boolean verify(byte[] signature, int offset, int length)

    The argument must be a byte array containing the signature. The argument must be a byte array containing the signature. This byte array would hold the signature bytes which were returned by a previous call to one of the sign methods.

    The verify method returns a boolean indicating whether or not the encoded signature is the authentic signature of the data supplied to the update method(s).

    A call to the verify method resets the signature object to its state when it was initialized for verification via a call to initVerify. 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.

    Alternatively, a new call can be made to initVerify specifying a different public key (to initialize the Signature object for verifying a signature from a different entity), or to initSign (to initialize the Signature object for generating a signature).

    Algorithm Parameters Classes

    Algorithm Parameter Specification Interfaces and Classes

    An algorithm parameter specification is a transparent representation of the sets of parameters used with an algorithm.

    A transparent representation of a set of parameters means that you can access each parameter value in the set individually. You can access these values through one of the get methods defined in the corresponding specification class (e.g., DSAParameterSpec defines getP, getQ, and getG methods, to access p, q, and g, respectively).

    In contrast, the AlgorithmParameters class supplies an opaque representation, in which you have no direct access to the parameter fields. You can only get the name of the algorithm associated with the parameter set (via getAlgorithm) and some kind of encoding for the parameter set (via getEncoded).

    The algorithm parameter specification interfaces and classes in the java.security.spec package are described in the following sections.

    The AlgorithmParameterSpec Interface

    AlgorithmParameterSpec is an interface to a transparent specification of cryptographic parameters.

    This interface contains no methods or constants. Its only purpose is to group (and provide type safety for) all parameter specifications. All parameter specifications must implement this interface.

    The DSAParameterSpec Class

    This class (which implements the AlgorithmParameterSpec interface) specifies the set of parameters used with the DSA algorithm. It has the following methods: 
    BigInteger getP()
BigInteger getQ()
BigInteger getG()
    These methods return the DSA algorithm parameters: the prime p, the sub-prime q, and the base g.

    The AlgorithmParameters Class

    The AlgorithmParameters class is an engine class that provides an opaque representation of cryptographic parameters.

    An opaque representation is one in which you have no direct access to the parameter fields; you can only get the name of the algorithm associated with the parameter set and some kind of encoding for the parameter set. This is in contrast to a transparent representation of parameters, in which you can access each value individually, through one of the get methods defined in the corresponding specification class. Note that you can call the AlgorithmParameters getParameterSpec method to convert an AlgorithmParameters object to a transparent specification (see the following section).

    Creating an AlgorithmParameters Object

    As with all engine classes, the way to get an AlgorithmParameters object for a particular type of algorithm is to call the getInstance static factory method on the AlgorithmParameters class: 

    static AlgorithmParameters getInstance(String algorithm)
    Note: The algorithm name is not case-sensitive.
    A caller may optionally specify the name of a provider or the Provider class, which will guarantee that the algorithm parameter implementation requested is from the named provider: 
    static AlgorithmParameters getInstance(String algorithm, String provider)
static AlgorithmParameters getInstance(String algorithm, Provider provider)

    Initializing an AlgorithmParameters Object

    Once an AlgorithmParameters object is instantiated, it must be initialized via a call to init, using an appropriate parameter specification or parameter encoding: 

    void init(AlgorithmParameterSpec paramSpec) 
void init(byte[] params)
void init(byte[] params, String format)
    In these init methods, params is an array containing the encoded parameters, and format is the name of the decoding format. In the init method with a params argument but no format argument, the primary decoding format for parameters is used. The primary decoding format is ASN.1, if an ASN.1 specification for the parameters exists.
    Note: AlgorithmParameters objects can be initialized only once. They are not reusable.

    Obtaining the Encoded Parameters

    A byte encoding of the parameters represented in an AlgorithmParameters object may be obtained via a call to getEncoded: 

    byte[] getEncoded()
    This method returns the parameters in their primary encoding format. The primary encoding format for parameters is ASN.1, if an ASN.1 specification for this type of parameters exists.

    If you want the parameters returned in a specified encoding format, use 

    byte[] getEncoded(String format)
    If format is null, the primary encoding format for parameters is used, as in the other getEncoded method.
    Note: In the default AlgorithmParameters implementation, supplied by the "SUN" provider, the format argument is currently ignored.

    Converting an AlgorithmParameters Object to a Transparent Specification

    A transparent parameter specification for the algorithm parameters may be obtained from an AlgorithmParameters object via a call to getParameterSpec: 

    AlgorithmParameterSpec getParameterSpec(Class paramSpec)
    paramSpec identifies the specification class in which the parameters should be returned. The specification class could be, for example, DSAParameterSpec.class to indicate that the parameters should be returned in an instance of the DSAParameterSpec class. (This class is in the java.security.spec package.)

    The AlgorithmParameterGenerator Class

    The AlgorithmParameterGenerator class is an engine class used to generate a set of parameters suitable for a certain algorithm (the algorithm specified when an AlgorithmParameterGenerator instance is created).

    Creating an AlgorithmParameterGenerator Object

    As with all engine classes, the way to get an AlgorithmParameterGenerator object for a particular type of algorithm is to call the getInstance static factory method on the AlgorithmParameterGenerator class: 

    static AlgorithmParameterGenerator getInstance(
                                   String algorithm)
    Note: The algorithm name is not case-sensitive.

    A caller may optionally specify the name of a provider or the Provider class, which will guarantee that the algorithm parameter generator implementation is from the named provider: 

    static AlgorithmParameterGenerator getInstance(
                                   String algorithm, 
                                   String provider)

static AlgorithmParameterGenerator getInstance(
                                   String algorithm, 
                                   Provider provider)

    Initializing an AlgorithmParameterGenerator Object

    The AlgorithmParameterGenerator object can be initialized in two different ways: an algorithm-independent manner or an algorithm-specific manner.

    The algorithm-independent approach uses the fact that all parameter generators share the concept of a "size" and a source of randomness. The measure of size is universally shared by all algorithm parameters, though it is interpreted differently for different algorithms. For example, in the case of parameters for the DSA algorithm, "size" corresponds to the size of the prime modulus, in bits. (See Appendix B: Algorithms for information about the sizes for specific algorithms.) When using this approach, algorithm-specific parameter generation values--if any--default to some standard values. One init method that takes these two universally shared types of arguments: 

    void init(int size, SecureRandom random);
    Another init method takes only a size argument and uses a system-provided source of randomness: 
    void init(int size)

    A third approach initializes a parameter generator object using algorithm-specific semantics, which are represented by a set of algorithm-specific parameter generation values supplied in an AlgorithmParameterSpec object: 

    void init(AlgorithmParameterSpec genParamSpec,
                          SecureRandom random)

void init(AlgorithmParameterSpec genParamSpec)
    To generate Diffie-Hellman system parameters, for example, the parameter generation values usually consist of the size of the prime modulus and the size of the random exponent, both specified in number of bits. (The Diffie-Hellman algorithm has been part of the JCE since JCE 1.2.)

    Generating Algorithm Parameters

    Once you have created and initialized an AlgorithmParameterGenerator object, you can use the generateParameters method to generate the algorithm parameters: 
    AlgorithmParameters generateParameters()

    Key Interfaces

    The Key interface is the top-level interface for all opaque keys. It defines the functionality shared by all opaque key objects.

    An opaque key representation is one in which you have no direct access to the key material that constitutes a key. In other words: "opaque" gives you limited access to the key--just the three methods defined by the Key interface (see below): getAlgorithm, getFormat, and getEncoded. This is in contrast to a transparent representation, in which you can access each key material value individually, through one of the get methods defined in the corresponding specification class.

    All opaque keys have three characteristics:

    An Algorithm
    The key algorithm for that key. The key algorithm is usually an encryption or asymmetric operation algorithm (such as DSA or RSA), which will work with those algorithms and with related algorithms (such as MD5 with RSA, SHA-1 with RSA, etc.) The name of the algorithm of a key is obtained using this method: 
    String getAlgorithm()
    An Encoded Form
    The external encoded form for the key used when a standard representation of the key is needed outside the Java Virtual Machine, as when transmitting the key to some other party. The key is encoded according to a standard format (such as X.509 or PKCS #8), and is returned using the method: 

    byte[] getEncoded()
    A Format
    The name of the format of the encoded key. It is returned by the method: 
    String getFormat()
    Keys are generally obtained through key generators, certificates, key specifications (using a KeyFactory), or a KeyStore implementation accessing a keystore database used to manage keys.

    It is possible to parse encoded keys, in an algorithm-dependent manner, using a KeyFactory.

    It is also possible to parse certificates, using a CertificateFactory.

    Here is a list of interfaces which extend the Key interface in the java.security.interfaces package:

    The PublicKey and PrivateKey Interfaces

    The PublicKey and PrivateKey interfaces (which both extend the Key interface) are methodless interfaces, used for type-safety and type-identification.

    Key Specification Interfaces and Classes

    Key specifications are transparent representations of the key material that constitutes a key. If the key is stored on a hardware device, its specification may contain information that helps identify the key on the device.

    A transparent representation of keys means that you can access each key material value individually, through one of the get methods defined in the corresponding specification class. For example, DSAPrivateKeySpec defines getX, getP, getQ, and getG methods, to access the private key x, and the DSA algorithm parameters used to calculate the key: the prime p, the sub-prime q, and the base g.

    This representation is contrasted with an opaque representation, as defined by the Key interface, in which you have no direct access to the key material fields. In other words, an "opaque" representation gives you limited access to the key--just the three methods defined by the Key interface: getAlgorithm, getFormat, and getEncoded.

    A key may be specified in an algorithm-specific way, or in an algorithm-independent encoding format (such as ASN.1). For example, a DSA private key may be specified by its components x, p, q, and g (see DSAPrivateKeySpec), or it may be specified using its DER encoding (see PKCS8EncodedKeySpec).

    In the following sections, we discuss the key specification interfaces and classes in the java.security.spec package.

    The KeySpec Interface

    This interface contains no methods or constants. Its only purpose is to group and provide type safety for all key specifications. All key specifications must implement this interface.

    The DSAPrivateKeySpec Class

    This class (which implements the KeySpec interface) specifies a DSA private key with its associated parameters. DSAPrivateKeySpec has the following methods: 
    BigInteger getX()
BigInteger getP()
BigInteger getQ()
BigInteger getG()
    These methods return the private key x, and the DSA algorithm parameters used to calculate the key: the prime p, the sub-prime q, and the base g.

    The DSAPublicKeySpec Class

    This class (which implements the KeySpec interface) specifies a DSA public key with its associated parameters. DSAPublicKeySpec has the following methods: 
    BigInteger getY()
BigInteger getP()
BigInteger getQ()
BigInteger getG()
    These methods return the public key y, and the DSA algorithm parameters used to calculate the key: the prime p, the sub-prime q, and the base g.

    The RSAPrivateKeySpec Class

    This class (which implements the KeySpec interface) specifies an RSA private key. RSAPrivateKeySpec has the following methods: 
    BigInteger getModulus()
BigInteger getPrivateExponent()
    These methods return the RSA modulus n and private exponent d values that constitute the RSA private key.

    The RSAPrivateCrtKeySpec Class

    This class (which extends the RSAPrivateKeySpec class) specifies an RSA private key, as defined in the PKCS #1 standard, using the Chinese Remainder Theorem (CRT) information values. RSAPrivateCrtKeySpec has the following methods (in addition to the methods inherited from its superclass RSAPrivateKeySpec): 
    BigInteger getPublicExponent()
BigInteger getPrimeP()
BigInteger getPrimeQ()
BigInteger getPrimeExponentP()
BigInteger getPrimeExponentQ()
BigInteger getCrtCoefficient()
    These methods return the public exponent e and the CRT information integers: the prime factor p of the modulus n, the prime factor q of n, the exponent d mod (p-1), the exponent d mod (q-1), and the Chinese Remainder Theorem coefficient (inverse of q) mod p.

    An RSA private key logically consists of only the modulus and the private exponent. The presence of the CRT values is intended for efficiency.

    The RSAMultiPrimePrivateCrtKeySpec Class

    This class (which extends the RSAPrivateKeySpec class) specifies an RSA multi-prime private key, as defined in the PKCS#1 v2.1, using the Chinese Remainder Theorem (CRT) information values. RSAMultiPrimePrivateCrtKeySpec has the following methods (in addition to the methods inherited from its superclass RSAPrivateKeySpec): 
    BigInteger getPublicExponent()
BigInteger getPrimeP()
BigInteger getPrimeQ()
BigInteger getPrimeExponentP()
BigInteger getPrimeExponentQ()
BigInteger getCrtCoefficient()
RSAOtherPrimeInfo[] getOtherPrimeInfo()
    These methods return the public exponent e and the CRT information integers: the prime factor p of the modulus n, the prime factor q of n, the exponent d mod (p-1), the exponent d mod (q-1), and the Chinese Remainder Theorem coefficient (inverse of q) mod p.

    Method getOtherPrimeInfo returns a copy of the otherPrimeInfo (defined in PKCS#1 v 2.1) or null if there are only two prime factors (p and q).

    An RSA private key logically consists of only the modulus and the private exponent. The presence of the CRT values is intended for efficiency.

    The RSAPublicKeySpec Class

    This class (which implements the KeySpec interface) specifies an RSA public key. RSAPublicKeySpec has the following methods: 
    BigInteger getModulus()
BigInteger getPublicExponent()
    These methods return the RSA modulus n and public exponent e values that constitute the RSA public key.

    The EncodedKeySpec Class

    This abstract class (which implements the KeySpec interface) represents a public or private key in encoded format. Its getEncoded method returns the encoded key: 
    abstract byte[] getEncoded();
    and its getFormat method returns the name of the encoding format: 
    abstract String getFormat();

    See the next sections for the concrete implementations PKCS8EncodedKeySpec and X509EncodedKeySpec.

    The PKCS8EncodedKeySpec Class

    This class, which is a subclass of EncodedKeySpec, represents the DER encoding of a private key, according to the format specified in the PKCS #8 standard. Its getEncoded method returns the key bytes, encoded according to the PKCS #8 standard. Its getFormat method returns the string "PKCS#8".

    The X509EncodedKeySpec Class

    This class, which is a subclass of EncodedKeySpec, represents the DER encoding of a public key, according to the format specified in the X.509 standard. Its getEncoded method returns the key bytes, encoded according to the X.509 standard. Its getFormat method returns the string "X.509".

    The KeyFactory Class

    The KeyFactory class is an engine class designed to provide conversions between opaque cryptographic keys (of type Key) and key specifications (transparent representations of the underlying key material).

    Key factories are bi-directional. They allow you to build an opaque key object from a given key specification (key material), or to retrieve the underlying key material of a key object in a suitable format.

    Multiple compatible key specifications can exist for the same key. For example, a DSA public key may be specified by its components y, p, q, and g (see DSAPublicKeySpec), or it may be specified using its DER encoding according to the X.509 standard (see X509EncodedKeySpec).

    A key factory can be used to translate between compatible key specifications. Key parsing can be achieved through translation between compatible key specifications, e.g., when you translate from X509EncodedKeySpec to DSAPublicKeySpec, you basically parse the encoded key into its components. For an example, see the end of the Generating/Verifying Signatures Using Key Specifications and KeyFactory section.

    Creating a KeyFactory Object

    As with all engine classes, the way to get a KeyFactory object for a particular type of key algorithm is to call the getInstance static factory method on the KeyFactory class: 

    static KeyFactory getInstance(String algorithm)
    Note: The algorithm name is not case-sensitive.
    A caller may optionally specify the name of a provider or the Provider class, which will guarantee that the implementation of the key factory requested is from the named provider. 
    static KeyFactory getInstance(String algorithm, String provider)
static KeyFactory getInstance(String algorithm, Provider provider)

    Converting Between a Key Specification and a Key Object

    If you have a key specification for a public key, you can obtain an opaque PublicKey object from the specification by using the generatePublic method: 

    PublicKey generatePublic(KeySpec keySpec)

    Similarly, if you have a key specification for a private key, you can obtain an opaque PrivateKey object from the specification by using the generatePrivate method: 

    PrivateKey generatePrivate(KeySpec keySpec)

    Converting Between a Key Object and a Key Specification

    If you have a Key object, you can get a corresponding key specification object by calling the getKeySpec method: 

    KeySpec getKeySpec(Key key, Class keySpec)
    keySpec identifies the specification class in which the key material should be returned. It could, for example, be DSAPublicKeySpec.class, to indicate that the key material should be returned in an instance of the DSAPublicKeySpec class.

    Please see the Examples section for more details.

    The CertificateFactory Class

    The CertificateFactory class is an engine class that defines the functionality of a certificate factory, which is used to generate certificate and certificate revocation list (CRL) objects from their encodings.

    A certificate factory for X.509 must return certificates that are an instance of java.security.cert.X509Certificate, and CRLs that are an instance of java.security.cert.X509CRL.

    Creating a CertificateFactory Object

    As with all engine classes, the way to get a CertificateFactory object for a particular certificate or CRL type is to call the getInstance static factory method on the CertificateFactory class: 

    static CertificateFactory getInstance(String type)
    Note: The type name is not case-sensitive.
    A caller may optionally specify the name of a provider or the Provider class, which will guarantee that the implementation of the certificate factory requested is from the named provider. 
    static CertificateFactory getInstance(String type, String provider)

static CertificateFactory getInstance(String type, Provider provider)

    Generating Certificate Objects

    To generate a certificate object and initialize it with the data read from an input stream, use the generateCertificate method: 
    final Certificate generateCertificate(InputStream inStream)
    To return a (possibly empty) collection view of the certificates read from a given input stream, use the generateCertificates method: 
    final Collection generateCertificates(InputStream inStream)

    Generating CRL Objects

    To generate a certificate revocation list (CRL) object and initialize it with the data read from an input stream, use the generateCRL method: 
    final CRL generateCRL(InputStream inStream)
    To return a (possibly empty) collection view of the CRLs read from a given input stream, use the generateCRLs method: 
    final Collection generateCRLs(InputStream inStream)

    Generating CertPath Objects

    To generate a CertPath object and initialize it with data read from an input stream, use one of the following generateCertPath methods (with or without specifying the encoding to be used for the data): 
    final CertPath generateCertPath(InputStream inStream)

final CertPath generateCertPath(InputStream inStream, 
                                String encoding)
    To generate a CertPath object and initialize it with a list of certificates, use the following method: 
    final CertPath generateCertPath(List certificates)
    To retrieve a list of the CertPath encodings supported by this certificate factory, you can call the getCertPathEncodings method: 
    final Iterator getCertPathEncodings()
    The default encoding will be listed first.

    The KeyPair Class

    The KeyPair class is a simple holder for a key pair (a public key and a private key). It has two public methods, one for returning the private key, and the other for returning the public key: 

    PrivateKey getPrivate()
PublicKey getPublic()

    The KeyPairGenerator Class

    The KeyPairGenerator class is an engine class used to generate pairs of public and private keys.

    There are two ways to generate a key pair: in an algorithm-independent manner, and in an algorithm-specific manner. The only difference between the two is the initialization of the object.

    Please see the Examples section for examples of calls to the methods documented below.

    Creating a KeyPairGenerator

    All key pair generation starts with a KeyPairGenerator. This generation is done using one of the factory methods on KeyPairGenerator: 

    static KeyPairGenerator getInstance(String algorithm)
static KeyPairGenerator getInstance(String algorithm, 
                                    String provider)
static KeyPairGenerator getInstance(String algorithm, 
                                    Provider provider)
    Note: The algorithm name is not case-sensitive.

    Initializing a KeyPairGenerator

    A key pair generator for a particular algorithm creates a public/private key pair that can be used with this algorithm. It also associates algorithm-specific parameters with each of the generated keys.

    A key pair generator needs to be initialized before it can generate keys. In most cases, algorithm-independent initialization is sufficient. But in other cases, algorithm-specific initialization is used.

    Algorithm-Independent Initialization

    All key pair generators share the concepts of a keysize and a source of randomness. The keysize is interpreted differently for different algorithms. For example, in the case of the DSA algorithm, the keysize corresponds to the length of the modulus. (See Appendix B: Algorithms for information about the keysizes for specific algorithms.)

    An initialize method takes two universally shared types of arguments: 

    void initialize(int keysize, SecureRandom random)
    Another initialize method takes only a keysize argument; it uses a system-provided source of randomness: 
    void initialize(int keysize)

    Since no other parameters are specified when you call the above algorithm-independent initialize methods, it is up to the provider what to do about the algorithm-specific parameters (if any) to be associated with each of the keys.

    If the algorithm is a "DSA" algorithm, and the modulus size (keysize) is 512, 768, or 1024, then the "SUN" provider uses a set of precomputed values for the p, q, and g parameters. If the modulus size is not one of the above values, the "SUN" provider creates a new set of parameters. Other providers might have precomputed parameter sets for more than just the three modulus sizes mentioned above. Still others might not have a list of precomputed parameters at all and instead always create new parameter sets.

    Algorithm-Specific Initialization

    For situations where a set of algorithm-specific parameters already exists (such as "community parameters" in DSA), there are two initialize methods that have an AlgorithmParameterSpec argument. One also has a SecureRandom argument, while the source of randomness is system-provided for the other: 

    void initialize(AlgorithmParameterSpec params,
                SecureRandom random)

void initialize(AlgorithmParameterSpec params)
    See the Examples section for more details.

    Generating a Key Pair

    The procedure for generating a key pair is always the same, regardless of initialization (and of the algorithm). You always call the following method from KeyPairGenerator: 

    KeyPair generateKeyPair()
    Multiple calls to generateKeyPair will yield different key pairs.

    Key Management

    A database called a "keystore" can be used to manage a repository of keys and certificates. (A certificate is a digitally signed statement from one entity, saying that the public key of some other entity has a particular value.)

    Keystore Location

    The keystore is by default stored in a file named .keystore in the user's home directory, as determined by the "user.home" system property. On Solaris systems "user.home" defaults to the user's home directory. On Win32 systems, given user name uName, "user.home" defaults to:

    • C:\Winnt\Profiles\uName on multi-user Windows NT systems
    • C:\Windows\Profiles\uName on multi-user Windows 95/98/2000 systems
    • C:\Windows on single-user Windows 95/98/2000 systems

    Keystore Implementation

    The KeyStore class supplies well-defined interfaces to access and modify the information in a keystore. It is possible for there to be multiple different concrete implementations, where each implementation is that for a particular type of keystore.

    Currently, there are two command-line tools that make use of KeyStore: keytool and jarsigner, and also a GUI-based tool named policytool. It is also used by the Policy reference implementation when it processes policy files specifying the permissions (allowed accesses to system resources) to be granted to code from various sources. Since KeyStore is publicly available, SDK users can write additional security applications that use it.

    There is a built-in default implementation, provided by Sun Microsystems. It implements the keystore as a file, utilizing a proprietary keystore type (format) named "JKS". It protects each private key with its individual password, and also protects the integrity of the entire keystore with a (possibly different) password.

    Keystore implementations are provider-based. More specifically, the application interfaces supplied by KeyStore are implemented in terms of a "Service Provider Interface" (SPI). That is, there is a corresponding abstract KeystoreSpi class, also in the java.security package, which defines the SPI methods that "providers" must implement. (The term "provider" refers to a package or a set of packages that supply a concrete implementation of a subset of services that can be accessed by the Java 2 SDK Security API.) Therefore, to provide a keystore implementation clients must implement a "provider" and supply a KeystoreSpi subclass implementation, as described in How to Implement a Provider for the Java Cryptography Architecture.

    Applications can choose different types of keystore implementations from different providers, using the getInstance factory method in the KeyStore class. A keystore type defines the storage and data format of the keystore information, and the algorithms used to protect private keys in the keystore and the integrity of the keystore itself. Keystore implementations of different types are not compatible.

    The default keystore type is "jks" (the proprietary type of the keystore implementation provided by the "SUN" provider). This is specified by the following line in the security properties file: 

    keystore.type=jks
    To have tools and other applications use a keystore implementation other than the default keystore, you can change that line to specify a different keystore type. Another solution would be to let users of your tools and applications specify a keystore type, and pass that value to the getInstance method of KeyStore.

    An example of the former approach is the following: If you have a provider package that supplies a keystore implementation for a keystore type called pkcs12, change the line to 

    keystore.type=pkcs12
    Note: Keystore type designations are not case-sensitive. For example, "JKS" would be considered the same as "jks".

    The KeyStore Class

    The KeyStore class is an engine class that supplies well-defined interfaces to access and modify the information in a keystore.

    This class represents an in-memory collection of keys and certificates. KeyStore manages two types of entries:

    Key Entry

    This type of keystore entry holds very sensitive cryptographic key information, which is stored in a protected format to prevent unauthorized access. Typically, a key stored in this type of entry is a secret key, or a private key accompanied by the certificate chain authenticating the corresponding public key.

    Private keys and certificate chains are used by a given entity for self-authentication using digital signatures. For example, software distribution organizations digitally sign JAR files as part of releasing and/or licensing software.

    Trusted Certificate Entry

    This type of entry contains a single public key certificate belonging to another party. It is called a trusted certificate because the keystore owner trusts that the public key in the certificate indeed belongs to the identity identified by the subject (owner) of the certificate.

    This type of entry can be used to authenticate other parties.

    Each entry in a keystore is identified by an "alias" string. In the case of private keys and their associated certificate chains, these strings distinguish among the different ways in which the entity may authenticate itself. For example, the entity may authenticate itself using different certificate authorities, or using different public key algorithms.

    Whether keystores are persistent, and the mechanisms used by the keystore if it is persistent, are not specified here. This convention allows use of a variety of techniques for protecting sensitive (e.g., private or secret) keys. Smart cards or other integrated cryptographic engines (SafeKeyper) are one option, and simpler mechanisms such as files may also be used (in a variety of formats).

    The main KeyStore methods are described below.

    Creating a KeyStore Object

    As with all engine classes, the way to get a KeyStore object is to call the getInstance static factory method on the KeyStore class: 

    static KeyStore getInstance(String type)

    A caller may optionally specify the name of a provider or the Provider class, which will guarantee that the implementation of the type requested is from the named provider: 

    static KeyStore getInstance(String type, String provider)
static KeyStore getInstance(String type, Provider provider)

    Loading a Particular Keystore into Memory

    Before a KeyStore object can be used, the actual keystore data must be loaded into memory via the load method: 
    final void load(InputStream stream, char[] password)
    The optional password is used to check the integrity of the keystore data. If no password is supplied, no integrity check is performed.

    To create an empty keystore, you pass null as the InputStream argument to the load method.

    Getting a List of the Keystore Aliases

    All keystore entries are accessed via unique aliases. The aliases method returns an enumeration of the alias names in the keystore: 

    final Enumeration aliases()

    Determining Keystore Entry Types

    As stated in The KeyStore Class, there are two different types of entries in a keystore.

    The following methods determine whether the entry specified by the given alias is a key/certificate or a trusted certificate entry, respectively: 

    final boolean isKeyEntry(String alias)
final boolean isCertificateEntry(String alias)

    Adding/Setting/Deleting Keystore Entries

    The setCertificateEntry method assigns a certificate to a specified alias: 
    final void setCertificateEntry(String alias, Certificate cert)
    If alias doesn't exist, a trusted certificate entry with that alias is created. If alias exists and identifies a trusted certificate entry, the certificate associated with it is replaced by cert.

    The setKeyEntry methods add (if alias doesn't yet exist) or set key entries: 

    final void setKeyEntry(String alias,
                       Key key, 
                       char[] password,
                       Certificate[] chain)

final void setKeyEntry(String alias,
                       byte[] key,
                       Certificate[] chain)
    In the method with key as a byte array, it is the bytes for a key in protected format. For example, in the keystore implementation supplied by the "SUN" provider, the key byte array is expected to contain a protected private key, encoded as an EncryptedPrivateKeyInfo as defined in the PKCS #8 standard. In the other method, the password is the password used to protect the key.

    The deleteEntry method deletes an entry: 

    final void deleteEntry(String alias)

    Getting Information from the Keystore

    The getKey method returns the key associated with the given alias. The key is recovered using the given password: 
    final Key getKey(String alias, char[] password)
    The following methods return the certificate, or certificate chain, respectively, associated with the given alias: 
    final Certificate getCertificate(String alias)
final Certificate[] getCertificateChain(String alias)
    You can determine the name (alias) of the first entry whose certificate matches a given certificate via the following: 
    final String getCertificateAlias(Certificate cert)

    Saving the KeyStore

    The in-memory keystore can be saved via the store method: 
    final void store(OutputStream stream, char[] password)
    The password is used to calculate an integrity checksum of the keystore data, which is appended to the keystore data.

    The SecureRandom Class

    The SecureRandom class is an engine class that provides the functionality of a random number generator.

    Creating a SecureRandom Object

    As with all engine classes, the way to get a SecureRandom object is to call the getInstance static factory method on the SecureRandom class: 

    static SecureRandom getInstance(String algorithm)

    A caller may optionally specify the name of a provider or the Provider class, which will guarantee that the implementation of the random number generation (RNG) algorithm requested is from the named provider: 

    static final SecureRandom getInstance(String algorithm,
                                      String provider)
static final SecureRandom getInstance(String algorithm,
                                      Provider provider)

    Seeding or Re-Seeding the SecureRandom Object

    The SecureRandom implementation attempts to completely randomize the internal state of the generator itself unless the caller follows the call to a getInstance method with a call to one of the setSeed methods: 

    synchronized public void setSeed(byte[] seed)
public void setSeed(long seed)
    Once the SecureRandom object has been seeded, it will produce bits as random as the original seeds.

    At any time a SecureRandom object may be re-seeded using one of the setSeed methods. The given seed supplements, rather than replaces, the existing seed; therefore, repeated calls are guaranteed never to reduce randomness.

    Using a SecureRandom Object

    To get random bytes, a caller simply passes an array of any length, which is then filled with random bytes: 

    synchronized public void nextBytes(byte[] bytes)

    Generating Seed Bytes

    If desired, it is possible to invoke the generateSeed method to generate a given number of seed bytes (to seed other random number generators, for example): 
    byte[] generateSeed(int numBytes)