How to Implement a Provider for the JavaTM Cryptography Architecture


Last Modified: 10 June 1998

Introduction
Who Should Read This Document
Related Documentation


Engine Classes and Corresponding SPI Classes


Steps to Implement and Integrate a Provider
Step 1: Write your Service Implementation Code
Step 2: Give your Provider a Name
Step 3: Write your "Master Class," a subclass of Provider
Step 4: Compile your Code
Step 5: Prepare for Testing: Install the Provider
Step 6: Write and Compile Test Programs
Step 7: Run your Test Programs
Step 8: Document your Provider and its Supported Services
Step 9: Make your Class Files and Documentation Available to Clients


Further Implementation Details and Requirements
Alias Names
Service Interdependencies
Default Initializations
Default Key Pair Generator Parameter Requirements
Signature Formats
DSA Interfaces and their Required Implementations
RSA Interfaces and their Required Implementations
Interfaces for Other Algorithm Types
Algorithm Parameter Specification Interfaces and Classes
Key Specification Interfaces and Classes Required by Key Factories


Appendix A: The "SUN" Provider's Master Class

Appendix B: The java.security Master Properties File

Introduction

JDK 1.1 introduced the notion of a Cryptography Package Provider, or "provider" for short. This term refers to a package (or a set of packages) that supply a concrete implementation of a subset of the cryptography aspects of the Java Security API.

In JDK 1.1 a provider could, for example, contain an implementation of one or more digital signature algorithms, message digest algorithms, and key generation algorithms. JDK 1.2 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.

A program wishing to use cryptography functionality 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 an implementation from a particular provider is desired, the program can request that provider by name, along with the service desired.

Each JDK installation has one or more provider packages installed. Clients may configure their runtimes 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 algorithms when no particular provider is requested.

JDK 1.2 comes standard with a default provider, named "SUN". The "SUN" provider package includes:

New providers may be added statically or dynamically. Clients may also query which providers are currently installed.

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.

Who Should Read This Document

This document is intended for experienced programmers wishing to create their own provider packages supplying cryptographic service implementations. It documents what you need to do in order to integrate your provider into Java Security so that your algorithms and other services can be found when Java Security API clients request them. Programmers that only need to use the Java Security API to access existing cryptography algorithms and other services do not need to read this document.

Related Documentation

This document assumes you have already read the Java Cryptography Architecture API Specification and Reference.

It also discusses various classes and interfaces in the Java Security API. The complete reference documentation for the relevant Security API packages can be found in:

Engine Classes and Corresponding Service Provider Interface Classes

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 JDK1.2 Java Security package related to cryptography, including the engine classes. Users of the API request and utilize instances of the engine classes to carry out corresponding operations. The following engine classes are defined in JDK 1.2:

Note: A "generator" creates objects with brand-new contents, whereas a "factory" creates objects from existing material (e.g., 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 (see next paragraph) would be that for a specific kind of signature algorithm, such as SHA1 with DSA, SHA1 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 Service Provider Interface 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 Key Specification Interfaces and Classes Required by Key Factories.) The actual implementation supplied in a KeyFactorySpi subclass would be that for a specific type of keys, e.g., DSA public and private keys.

Steps to Implement and Integrate a Provider

The steps required in order to implement a provider and integrate it into Java Security are the following:

Step 1: Write your Service Implementation Code

The first thing you need to do is write the code supplying algorithm-specific implementations of the cryptographic services you want to support.

In JDK 1.2, you can supply signature, message digest, key pair generation, and (pseudo-)random number generation algorithms, as well as key and certificate factories and keystore creation and management, algorithm parameter management, and algorithm parameter generation services.

For each cryptographic service, you need to create a subclass of the appropriate SPI class: SignatureSpi, MessageDigestSpi, KeyPairGeneratorSpi, SecureRandomSpi, AlgorithmParameterGeneratorSpi, AlgorithmParametersSpi, KeyFactorySpi, CertificateFactorySpi, or KeyStoreSpi. (See "Engine Classes and Corresponding SPI Classes".)

In your subclass, you need to

  1. supply implementations for the abstract methods, whose names usually begin with "engine". See Further Implementation Details and Requirements for additional information.

  2. ensure there is a public constructor without any arguments. Here's why: When one of your services is requested, Java Security looks up the subclass implementing that service, as specified by a property in your "master class" (see Step 3). Java Security then creates the Class object associated with your subclass, and creates an instance of your subclass by calling the newInstance method on that Class object. newInstance requires your subclass to have a public constructor without any parameters.

    A default constructor without arguments will automatically be generated if your subclass doesn't have any constructors. But if your subclass defines any constructors, you must explicitly define a public constructor without arguments.

Step 2: Give your Provider a Name

Decide on a name for your provider. This is the name to be used by client applications to refer to your provider.

Step 3: Write your "Master Class", a subclass of Provider

The third step is to create a subclass of the Provider class.

Your subclass should be a final class, and its constructor should

For further master class property setting examples, see Appendix A to view the current JDK 1.2 Sun.java source file. This shows how the Sun class constructor sets all the properties for the "SUN" provider.

Note: The Provider subclass can get its information from wherever it wants. Thus, the information can be hard-wired in, or retrieved at runtime, e.g., from a file.

Step 4: Compile your Code

After you have created your implementation code (Step 1), given your provider a name (Step 2), and created the master class (Step 3), use the Java compiler to compile your files.

Step 5: Prepare for Testing: Install the Provider

In order to prepare for testing your provider, you must install it in the same manner as will be done by clients wishing to use it. The installation enables Java Security to find your algorithm implementations when clients request them.

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

Installing the Provider Classes

The first thing you must do is make your classes available so that they can be found when requested. You ship your provider classes as a JAR (Java ARchive) or ZIP file. There are a couple possible ways of installing the provider classes:

Configuring the Provider

The next step is to add the provider to your list of approved providers. This is done statically by editing the java.security file in the lib/security (lib\security on Windows) directory of the JDK. Thus, if the JDK is installed in a directory called jdk1.2, the file is

  • jdk1.2/lib/security/java.security (Solaris)

  • jdk1.2\lib\security\java.security (Windows)

For each provider, this file should have a statement of 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 fully qualified name of the provider's "master class", which you implemented in Step 3. This class is always a subclass of the Provider class.

Whenever the JDK is installed, it contains one built-in (default) provider, the provider referred to as "SUN". The java.security file has just the following provider specification: 

    security.provider.1=sun.security.provider.Sun
(Recall that the "SUN" provider's master class is the Sun class in the sun.security.provider package.)

Suppose that your master class is the Acme class in the COM.acme.provider package, and that you would like to make your provider the second preferred provider. To do so, add the following line to the java.security file below the line for the "SUN" provider: 

    security.provider.2=COM.acme.provider.Acme
Note: Providers may also be registered dynamically. To do so, a program (such as your test program, to be written in Step 7) can 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 the Security class section of the Java Cryptography Architecture API Specification and Reference.

Step 6: Write and Compile your Test Programs

Write and compile one or more test programs that test your provider's incorporation into the Security API as well as the correctness of its algorithm(s). Create any supporting files needed, such as those for test data to be hashed or signed.

The first tests your program should perform are ones to ensure that your provider is found, and that its name, version number, and additional information is as expected. To do so, you could write code like the following, substituting your provider name for "MyPro": 

    import java.security.*;

    Provider p = Security.getProvider("MyPro");
    
    System.out.println("MyPro provider name is " + p.getName());
    System.out.println("MyPro provider version # is " + p.getVersion());
    System.out.println("MyPro provider info is " + p.getInfo());

Next, you should ensure that your services are found. For instance, if you implemented a SHA-1 message digest algorithm, you could check to ensure it's found when requested by using the following code (again substituting your provider name for "MyPro"): 

    MessageDigest sha = MessageDigest.getInstance("SHA", "MyPro");

    System.out.println("My MessageDigest algorithm name is " + 
        sha.getAlgorithm());

If you don't specify a provider name in the call to getInstance, all registered providers will be searched, in preference order (see Configuring the Provider), until one implementing the algorithm is found.

Step 7: Run your Test Programs

Run your test program(s). Debug your code and continue testing as needed. If the Java Security API cannot seem to find one of your algorithms, review the steps above and ensure they are all completed.

Step 8: Document your Provider and its Supported Services

The next-to-last step is to write documentation for your clients. At the minimum, you need to specify In addition, your documentation should specify anything else of interest to clients, such as any default algorithm parameters.

Message Digests

For each message digest algorithm, tell whether or not your implementation is cloneable. This is not technically necessary, but it may save clients some time and coding by telling them whether or not intermediate hashes may be possible through cloning. Clients who do not know whether or not a message digest implementation is cloneable can find out by attempting to clone the MessageDigest object and catching the potential exception, as illustrated by the following example: 

try {
   // try and clone it
    /* compute the hash for i1 */
    sha.update(i1); 
    byte[] i1Hash = sha.clone().digest();

    /* compute the hash for i1 and i2 */
    sha.update(i2); 
    byte[] i12Hash = sha.clone().digest(); 

    /* compute the hash for i1, i2 and i3 */
    sha.update(i3); 
    byte[] i123Hash = sha.digest();
} catch (CloneNotSupportedException cnse) {
  // have to use an approach not involving cloning
}
where

Signature Algorithms

If you implement a signature algorithm, you should document the format in which the signature (generated by one of the sign methods) is encoded. For example, the SHA1withDSA signature algorithm supplied by the "SUN" provider encodes the signature as a standard ASN.1 SEQUENCE of two integers, r and s.

Random Number Generation (SecureRandom) Algorithms

For a random number generation algorithm, provide information regarding how "random" the numbers generated are, and the quality of the seed when the random number generator is self-seeding. Also note what happens when a SecureRandom object (and its encapsulated SecureRandomSpi implementation object) is deserialized: If subsequent calls to the nextBytes method (which invokes the engineNextBytes method of the encapsulated SecureRandomSpi object) of the restored object yield the exact same (random) bytes as the original object would, then let users know that if this behaviour is undesirable, they should seed the restored random object by calling its setSeed method.

Key Pair Generators

For a key pair generator algorithm, in case the client does not explicitly initialize the key pair generator (via a call to an initialize method), each provider must supply and document a default initialization. For example, the "SUN" provider uses a default modulus size (strength) of 1024 bits.

Key Factories

A provider should document all the key specifications supported by its key factory.

Certificate Factories

A provider should document what types of certificates (and their version numbers, if relevant), can be created by the factory.

Keystores

A provider should document any relevant information regarding the keystore implementation, such as its underlying data format.

Algorithm Parameter Generators

In case the client does not explicitly initialize the algorithm parameter generator (via a call to an init method in the AlgorithmParameterGenerator engine class), each provider must supply and document a default initialization. For example, the "SUN" provider uses a default modulus prime size of 1024 bits for the generation of DSA parameters.

Step 9: Make your Class Files and Documentation Available to Clients

The final step is to make your class files and documentation available to clients in whatever form (.class files, zip files, JAR files, ...) and methods (web download, floppy, mail, ...) you feel are appropriate.

Further Implementation Details and Requirements

Alias Names

For many cryptographic algorithms and types, there is a single official "standard name" defined in Appendix A of the Java Cryptography Architecture API Specification & Reference.

For example, "MD5" is the standard name for the RSA-MD5 Message Digest algorithm defined by RSA DSI in RFC 1321.

In JDK 1.2, there is an aliasing scheme that enables clients to use aliases when referring to algorithms or types, rather than their standard names. For example, the "SUN" provider's master class (Sun.java) defines the alias "SHA1/DSA" for the algorithm whose standard name is "SHA1withDSA". Thus, the following statements are equivalent: 

    Signature sig = Signature.getInstance("SHA1withDSA", "SUN");

    Signature sig = Signature.getInstance("SHA1/DSA", "SUN");
Aliases can be defined in your "master class" (see Step 3). To define an alias, create a property named 
    Alg.Alias.engineClassName.aliasName

where engineClassName is the name of an engine class (e.g., Signature), and aliasName is your alias name. The value of the property must be the standard algorithm (or type) name for the algorithm (or type) being aliased.

As an example, the "SUN" provider defines the alias "SHA1/DSA" for the signature algorithm whose standard name is "SHA1withDSA" by setting a property named Alg.Alias.Signature.SHA1/DSA to have the value SHA1withDSA via the following: 

    put("Alg.Alias.Signature.SHA1/DSA", "SHA1withDSA");

Currently, aliases defined by the "SUN" provider are available to all clients, no matter which provider clients request. For example, if you create a provider named "MyPro" that implements the SHA1withDSA algorithm, then even if you don't define any aliases for it, the "SHA1/DSA" alias defined by "SUN" can be used to refer to your provider's SHA1withDSA implementation as follows: 

    Signature sig = Signature.getInstance("SHA1/DSA", "MyPro");
WARNING: The aliasing scheme may be changed or eliminated in future releases.

Service Interdependencies

Some algorithms require the use of other types of algorithms. For example, a signature algorithm usually needs to use a message digest algorithm in order to sign and verify data.

If you are implementing one type of algorithm that requires another, you can do one of the following:

  1. Provide your own implementations for both.

  2. Let your implementation of one algorithm use an instance of the other type of algorithm, as supplied by the default "SUN" provider that is included with every JDK installation. For example, if you are implementing a signature algorithm that requires a message digest algorithm, you can obtain an instance of a class implementing the MD5 message digest algorithm by calling 
        MessageDigest.getInstance("MD5", "SUN")

  3. Let your implementation of one algorithm use an instance of the other type of algorithm, as supplied by another specific provider. This is only appropriate if you are sure that all clients who will use your provider will also have the other provider installed.

  4. Let your implementation of one algorithm use an instance of the other type of algorithm, as supplied by another (unspecified) provider. That is, you can request an algorithm by name, but without specifying any particular provider, as in 
        MessageDigest.getInstance("MD5")
    This is only appropriate if you are sure that there will be at least one implementation of the requested algorithm (in this case, MD5) installed on each Java platform where your provider will be used.

Here are some common types of algorithm interdependencies:

Signature and Message Digest Algorithms

A signature algorithm often requires use of a message digest algorithm. For example, the SHA1withDSA signature algorithm requires the SHA-1 message digest algorithm.

Signature and (Pseudo-)Random Number Generation Algorithms

A signature algorithm often requires use of a (pseudo-)random number generation algorithm. For example, such an algorithm is required in order to generate a DSA signature.

Key Pair Generation and Message Digest Algorithms

A key pair generation algorithm often requires use of a message digest algorithm. For example, DSA keys are generated using the SHA-1 message digest algorithm.

Algorithm Parameter Generation and Message Digest Algorithms

An algorithm parameter generator often requires use of a message digest algorithm. For example, DSA parameters are generated using the SHA-1 message digest algorithm.

KeyStores and Message Digest Algorithms

A keystore implementation will often utilize a message digest algorithm to compute keyed hashes (where the "key" is a user-provided password) to check the integrity of a keystore and make sure that the keystore has not been tampered with.

Key Pair Generation Algorithms and Algorithm Parameter Generators

A key pair generation algorithm sometimes needs to generate a new set of algorithm parameters. It can either generate the parameters directly, or use an algorithm parameter generator.

Key Pair Generation, Algorithm Parameter Generation, and (Pseudo-)Random Number Generation Algorithms

A key pair generation algorithm may require a source of randomness in order to generate a new key pair and possibly a new set of parameters associated with the keys. That source of randomness is represented by a SecureRandom object. The implementation of the key pair generation algorithm may generate the key parameters itself, or may use an algorithm parameter generator to generate them, in which case it may or may not initialize the algorithm parameter generator with a source of randomness.

Algorithm Parameter Generators and Algorithm Parameters

An algorithm parameter generator's engineGenerateParameters method must return an AlgorithmParameters instance.

Signature and Key Pair Generation Algorithms or Key Factories

If you are implementing a signature algorithm, your implementation's engineInitSign and engineInitVerify methods will require passed-in keys that are valid for the underlying algorithm (e.g., DSA keys for the DSS algorithm). You can do one of the following:

  1. Also create your own classes implementing appropriate interfaces (e.g. classes implementing the DSAPrivateKey and DSAPublicKey interfaces from the package java.security.interfaces), and create your own key pair generator and/or key factory returning keys of those types. Require the keys passed to engineInitSign and engineInitVerify to be the types of keys you have implemented, that is, keys generated from your key pair generator or key factory. Or you can

  2. Accept keys from other key pair generators or other key factories, as long as they are instances of appropriate interfaces that enable your signature implementation to obtain the information it needs (such as the private and public keys and the key parameters). For example, the engineInitSign method for a DSS Signature class could accept any private keys that are instances of java.security.interfaces.DSAPrivateKey.

KeyStores and Key and Certificate Factories

A keystore implementation will often utilize a key factory to parse the keys stored in the keystore, and a certificate factory to parse the certificates stored in the keystore.

Default Initializations

In case the client does not explicitly initialize a key pair generator or an algorithm parameter generator, each provider of such a service must supply (and document) a default initialization. For example, the "SUN" provider uses a default modulus size (strength) of 1024 bits for the generation of DSA parameters.

Default Key Pair Generator Parameter Requirements

If you implement a key pair generator, your implementation should supply default parameters that are used when clients don't specify parameters. The documentation you supply (Step 8) should state what the default parameters are.

For example, the DSA key pair generator in the "SUN" provider supplies a set of pre-computed p, q, and g default values for the generation of 512, 768, and 1024-bit key pairs. The following p, q, and g values are used as the default values for the generation of 1024-bit DSA key pairs: 

p = fd7f5381 1d751229 52df4a9c 2eece4e7 f611b752 3cef4400 c31e3f80
    b6512669 455d4022 51fb593d 8d58fabf c5f5ba30 f6cb9b55 6cd7813b
    801d346f f26660b7 6b9950a5 a49f9fe8 047b1022 c24fbba9 d7feb7c6
    1bf83b57 e7c6a8a6 150f04fb 83f6d3c5 1ec30235 54135a16 9132f675
    f3ae2b61 d72aeff2 2203199d d14801c7

q = 9760508f 15230bcc b292b982 a2eb840b f0581cf5
	 
g = f7e1a085 d69b3dde cbbcab5c 36b857b9 7994afbb fa3aea82 f9574c0b
    3d078267 5159578e bad4594f e6710710 8180b449 167123e8 4c281613
    b7cf0932 8cc8a6e1 3c167a8b 547c8d28 e0a3ae1e 2bb3a675 916ea37f
    0bfa2135 62f1fb62 7a01243b cca4f1be a8519089 a883dfe1 5ae59f06
    928b665e 807b5525 64014c3b fecf492a

(The p and q values given here were generated by the prime generation standard, using the 160-bit 

SEED:  8d515589 4229d5e6 89ee01e6 018a237e 2cae64cd
With this seed, the algorithm found p and q when the counter was at 92.)

Signature Formats

If you implement a signature algorithm, the documentation you supply (Step 8) should specify the format in which the signature (generated by one of the sign methods) is encoded.

For example, the SHA1withDSA signature algorithm supplied by the "SUN" provider encodes the signature as a standard ASN.1 sequence of two ASN.1 INTEGER values: r and s, in that order: 

	SEQUENCE ::= {
		r INTEGER,
		s INTEGER }

DSA Interfaces and their Required Implementations

The Java Security API contains the following interfaces (in the java.security.interfaces package) for the convenience of programmers implementing DSA services: The following sections discuss requirements for implementations of these interfaces.

DSAKeyPairGenerator Implementation

This interface is obsolete. It used to be needed to enable clients to provide DSA-specific parameters to be used rather than the default parameters your implementation supplies. However, in JDK 1.2 it is no longer necessary; a new KeyPairGenerator initialize method that takes an AlgorithmParameterSpec parameter enables clients to indicate algorithm-specific parameters.

DSAParams Implementation

If you are implementing a DSA key pair generator, you need a class implementing DSAParams for holding and returning the p, q, and g parameters.

A DSAParams implementation is also required if you implement the DSAPrivateKey and DSAPublicKey interfaces. DSAPublicKey and DSAPrivateKey both extend the DSAKey interface, which contains a getParams method that must return a DSAParams object. See DSAPrivateKey and DSAPublicKey Implementations for more information.

Note: there is a DSAParams implementation built into the JDK: the java.security.spec.DSAParameterSpec class.

DSAPrivateKey and DSAPublicKey Implementations

If you implement a DSA key pair generator or key factory, you need to create classes implementing the DSAPrivateKey and DSAPublicKey interfaces.

If you implement a DSA key pair generator, your generateKeyPair method (in your KeyPairGeneratorSpi subclass) will return instances of your implementations of those interfaces.

If you implement a DSA key factory, your engineGeneratePrivate method (in your KeyFactorySpi subclass) will return an instance of your DSAPrivateKey implementation, and your engineGeneratePublic method will return an instance of your DSAPublicKey implementation.

Also, your engineGetKeySpec and engineTranslateKey methods will expect the passed-in key to be an instance of a DSAPrivateKey or DSAPublicKey implementation. The getParams method provided by the interface implementations is useful for obtaining and extracting the parameters from the keys and then using the parameters, for example as parameters to the DSAParameterSpec constructor called to create a parameter specification from parameter values that could be used to initialize a KeyPairGenerator object for DSA.

If you implement a DSA signature algorithm, your engineInitSign method (in your SignatureSpi subclass) will expect to be passed a DSAPrivateKey and your engineInitVerify method will expect to be passed a DSAPublicKey.

Please note: The DSAPublicKey and DSAPrivateKey interfaces define a very generic, provider-independent interface to DSA public and private keys, respectively. The engineGetKeySpec and engineTranslateKey methods (in your KeyFactorySpi subclass) could additionally check if the passed-in key is actually an instance of their provider's own implementation of DSAPrivateKey or DSAPublicKey, e.g., to take advantage of provider-specific implementation details. The same is true for the DSA signature algorithm engineInitSign and engineInitVerify methods (in your SignatureSpi subclass).

To see what methods need to be implemented by classes that implement the DSAPublicKey and DSAPrivateKey interfaces, first note the following interface signatures: 

  In the java.security.interfaces package:

    public interface DSAPrivateKey extends DSAKey, 
                                     java.security.PrivateKey

    public interface DSAPublicKey extends DSAKey, 
                                    java.security.PublicKey

    public interface DSAKey

  In the java.security package:

    public interface PrivateKey extends Key

    public interface PublicKey extends Key

    public interface Key extends java.io.Serializable

In order to implement the DSAPrivateKey and DSAPublicKey interfaces, you must implement the methods they define as well as those defined by interfaces they extend, directly or indirectly.

Thus, for private keys, you need to supply a class that implements

  • the getX method from the DSAPrivateKey interface.

  • the getParams method from the java.security.interfaces.DSAKey interface, since DSAPrivateKey extends DSAKey. Note: The getParams method returns a DSAParams object, so you must also have a DSAParams implementation.

  • the getAlgorithm, getEncoded, and getFormat methods from the java.security.Key interface, since DSAPrivateKey extends java.security.PrivateKey, and PrivateKey extends Key. Similarly, for public DSA keys, you need to supply a class that implements

RSA Interfaces and their Required Implementations

The Java Security API contains the following interfaces (in the java.security.interfaces package) for the convenience of programmers implementing RSA services: The following sections discuss requirements for implementations of these interfaces.

RSAPrivateKey, RSAPrivateCrtKey, and RSAPublicKey Implementations

If you implement an RSA key pair generator or key factory, you need to create classes implementing the RSAPrivateKey (and/or RSAPrivateCrtKey) and RSAPublicKey interfaces. (RSAPrivateCrtKey is the interface to an RSA private key, using the Chinese Remainder Theorem (CRT) representation.)

If you implement an RSA key pair generator, your generateKeyPair method (in your KeyPairGeneratorSpi subclass) will return instances of your implementations of those interfaces.

If you implement an RSA key factory, your engineGeneratePrivate method (in your KeyFactorySpi subclass) will return an instance of your RSAPrivateKey (or RSAPrivateCrtKey) implementation, and your engineGeneratePublic method will return an instance of your RSAPublicKey implementation.

Also, your engineGetKeySpec and engineTranslateKey methods will expect the passed-in key to be an instance of an RSAPrivateKey, RSAPrivateCrtKey, or RSAPublicKey implementation.

If you implement an RSA signature algorithm, your engineInitSign method (in your SignatureSpi subclass) will expect to be passed either an RSAPrivateKey or an RSAPrivateCrtKey, and your engineInitVerify method will expect to be passed an RSAPublicKey.

Please note: The RSAPublicKey, RSAPrivateCrtKey, and RSAPrivateKey interfaces define a very generic, provider-independent interface to RSA public and private keys. The engineGetKeySpec and engineTranslateKey methods (in your KeyFactorySpi subclass) could additionally check if the passed-in key is actually an instance of their provider's own implementation of RSAPrivateKey, RSAPrivateCrtKey, or RSAPublicKey, e.g., to take advantage of provider-specific implementation details. The same is true for the RSA signature algorithm engineInitSign and engineInitVerify methods (in your SignatureSpi subclass).

To see what methods need to be implemented by classes that implement the RSAPublicKey, RSAPrivateCrtKey, and RSAPrivateKey interfaces, first note the following interface signatures: 

  In the java.security.interfaces package:

    public interface RSAPrivateKey extends java.security.PrivateKey

    public interface RSAPrivateCrtKey extends RSAPrivateKey

    public interface RSAPublicKey extends java.security.PublicKey


  In the java.security package:

    public interface PrivateKey extends Key

    public interface PublicKey extends Key

    public interface Key extends java.io.Serializable

In order to implement the RSAPrivateKey, RSAPrivateCrtKey, and RSAPublicKey interfaces, you must implement the methods they define as well as those defined by interfaces they extend, directly or indirectly.

Thus, for RSA private keys, you need to supply a class that implements

  • the getModulus and getPrivateExponent methods from the RSAPrivateKey interface.

  • the getAlgorithm, getEncoded, and getFormat methods from the java.security.Key interface, since RSAPrivateKey extends java.security.PrivateKey, and PrivateKey extends Key.

    Similarly, for RSA private keys using the Chinese Remainder Theorem (CRT) representation, you need to supply a class that implements

    • all the methods listed above for RSA private keys, since RSAPrivateCrtKey extends java.security.interfaces.RSAPrivateKey.

    • the getPublicExponent, getPrimeP, getPrimeQ, getPrimeExponentP, getPrimeExponentQ, and getCrtCoefficient methods from the RSAPrivateCrtKey interface.

      For public RSA keys, you need to supply a class that implements

      • the getModulus and getPublicExponent methods from the RSAPublicKey interface.

      • the getAlgorithm, getEncoded, and getFormat methods from the java.security.Key interface, since RSAPublicKey extends java.security.PublicKey, and PublicKey extends Key.

Interfaces for Other Algorithm Types

As noted above, the Java Security API contains interfaces for the convenience of programmers implementing DSA and RSA services. The API does not at this time contain similar interfaces for any other type of algorithm. Thus, you need to define your own.

If you are implementing a key pair generator for a different algorithm, you should create an interface with one or more initialize methods that clients can call when they want to provide algorithm-specific parameters to be used rather than the default parameters your implementation supplies. Your subclass of KeyPairGeneratorSpi should implement this interface.

For private and public keys for non-DSA and non-RSA algorithms, there are currently no java.security.interfaces interfaces corresponding to the DSAPrivateKey and DSAPublicKey ones for DSA and the RSAPrivateKey, RSAPrivateCrtKey, and RSAPublicKey ones for RSA. It is recommended that you create similar interfaces and provide implementation classes. Your public key interface should extend the PublicKey interface. Similarly, your private key interface should extend the PrivateKey interface.

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 parameters means that you can access each value individually, through one of the "get" methods defined in the corresponding specification class (e.g., DSAParameterSpec defines getP, getQ, and getG methods, to access the p, q, and g parameters, respectively).

This is contrasted with an opaque representation, as supplied by the AlgorithmParameters engine class, in which you have no direct access to the key material values; 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).

If you supply an AlgorithmParametersSpi, AlgorithmParameterGeneratorSpi, or KeyPairGeneratorSpi implementation, you must utilize the AlgorithmParameterSpec interface, since each of those classes contain methods that take an AlgorithmParameterSpec parameter. Such methods need to determine which actual implementation of that interface has been passed in, and act accordingly.

JDK 1.2 contains one AlgorithmParameterSpec implementation, the DSAParameterSpec class. If you are working with DSA algorithm parameters, you can utilize this class. If you are operating on algorithm parameters that should be for a different type of algorithm, you will need to supply your own AlgorithmParameterSpec implementation appropriate for that type of algorithm.

JDK 1.2 defines the following algorithm parameter specification interfaces and classes in the java.security.spec package:

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 and DSAParams interfaces) specifies the set of parameters used with the DSA algorithm. It has the following methods: 
    public BigInteger getP()

    public BigInteger getQ()

    public BigInteger getG()
These methods return the DSA algorithm parameters: the prime p, the sub-prime q, and the base g.

Many types of DSA services will find this class useful - for example, it is utilized by the DSA signature, key pair generator, algorithm parameter generator, and algorithm parameters classes implemented by the "SUN" provider. As a specific example, an algorithm parameters implementation must include an implementation for the getParameterSpec method, which returns an AlgorithmParameterSpec. The DSA algorithm parameters implementation supplied by "SUN" returns an instance of the DSAParameterSpec class.

Key Specification Interfaces and Classes Required by Key Factories

A key factory provides bi-directional conversions between opaque keys (of type Key) and key specifications. If you implement a key factory, you thus need to understand and utilize key specifications. In some cases, you also need to implement your own key specifications. Further information about key specifications, the interfaces and classes supplied in JDK 1.2, and key factory requirements with respect to specifications, is provided below.

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, java.security.spec.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 is contrasted with an opaque representation, as defined by the Key interface, in which you have no direct access to the parameter 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).

JDK 1.2 defines the following 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.

JDK 1.2 supplies several classes implementing the KeySpec interface: DSAPrivateKeySpec, DSAPublicKeySpec, RSAPrivateKeySpec, RSAPublicKeySpec, EncodedKeySpec, PKCS8EncodedKeySpec, and X509EncodedKeySpec.

If your provider uses key types (e.g., Your_PublicKey_type and Your_PrivateKey_type) for which the JDK does not already provide corresponding KeySpec classes, there are two possible scenarios, one of which requires that you implement your own key specifications:

  1. If your users will never have to access specific key material values of your key type, you will not have to provide any KeySpec classes for your key type.

    In this scenario, your users will always create Your_PublicKey_type and Your_PrivateKey_type keys through the appropriate KeyPairGenerator supplied by your provider for that key type. If they want to store the generated keys for later usage, they retrieve the keys' encodings (using the getEncoded method of the Key interface). When they want to create an Your_PublicKey_type or Your_PrivateKey_type key from the encoding (e.g., in order to initialize a Signature object for signing or verification), they create an instance of X509EncodedKeySpec or PKCS8EncodedKeySpec from the encoding, and feed it to the appropriate KeyFactory supplied by your provider for that algorithm, whose generatePublic and generatePrivate methods will return the requested PublicKey (an instance of Your_PublicKey_type) or PrivateKey (an instance of Your_PrivateKey_type) object, respectively.

  2. If you anticipate a need for users to access specific key material values of your key type, or to construct a key of your key type from key material and associated parameter values, rather than from its encoding (as in the above case), you have to specify new KeySpec classes (classes that implement the KeySpec interface) with the appropriate constructor methods and "get" methods for returning key material fields and associated parameter values for your key type. You will specify those classes in a similar manner as is done by the DSAPrivateKeySpec and DSAPublicKeySpec classes provided in the JDK. You need to ship those classes along with your provider classes, for example, as part of your provider JAR file.

The DSAPrivateKeySpec Class

This class (which implements the KeySpec Interface) specifies a DSA private key with its associated parameters. It has the following methods: 
    public BigInteger getX()

    public BigInteger getP()

    public BigInteger getQ()

    public 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. It has the following methods: 
    public BigInteger getY()

    public BigInteger getP()

    public BigInteger getQ()

    public 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. It has the following methods: 
    public BigInteger getModulus()

    public 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. It has the following methods (in addition to the methods inherited from its superclass RSAPrivateKeySpec): 
    public BigInteger getPublicExponent()

    public BigInteger getPrimeP()

    public BigInteger getPrimeQ()

    public BigInteger getPrimeExponentP()

    public BigInteger getPrimeExponentQ()

    public 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 RSAPublicKeySpec Class

This class (which implements the KeySpec Interface) specifies an RSA public key. It has the following methods: 
    public BigInteger getModulus()

    public 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: 
    public abstract byte[] getEncoded();
and its getFormat method returns the name of the encoding format: 
    public abstract String getFormat();

JDK 1.2 supplies two classes implementing the EncodedKeySpec interface: PKCS8EncodedKeySpec and X509EncodedKeySpec. If desired, you can supply your own EncodedKeySpec implementations for those or other types of key encodings.

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 or private 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".

Appendix A: The "SUN" Provider's Master Class

Below is a copy of the Sun.java file, which contains a class named Sun that is the master class for the provider named "SUN". (This provider is supplied with every JDK installation.)

As with all master classes, this class is a subclass of Provider. It specifies the class names and package locations of all the cryptographic service implementations supplied by the "SUN" provider. Java Security uses this information to look up the various algorithms and other services when they are requested.

This code is supplied as an example of a master class. 

/*
* Copyright 1996-1998 by Sun Microsystems, Inc.,
* 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
* All rights reserved.
*
* This software is the confidential and proprietary information
* of Sun Microsystems, Inc. ("Confidential Information").  You
* shall not disclose such Confidential Information and shall use
* it only in accordance with the terms of the license agreement
* you entered into with Sun.
*/

package sun.security.provider;

import java.io.*;
import java.util.*;
import java.security.*;

/**
* The SUN Security Provider.
*/

/**
* Defines the SUN provider.
*
* Algorithms supported, and their names:
*
* - SHA is the message digest scheme described in FIPS 180-1. 
*   Aliases for SHA are SHA-1 and SHA1.
*
* - SHA1withDSA is the signature scheme described in FIPS 186.
*   (SHA used in DSA is SHA-1: FIPS 186 with Change No 1.)
*   Aliases for SHA1withDSA are DSA, DSS, SHA/DSA, SHA-1/DSA, SHA1/DSA,
*   SHAwithDSA, DSAWithSHA1, and the object
*   identifier strings "OID.1.3.14.3.2.13", "OID.1.3.14.3.2.27" and
*   "OID.1.2.840.10040.4.3".
*
* - DSA is the key generation scheme as described in FIPS 186.
*   Aliases for DSA include the OID strings "OID.1.3.14.3.2.12"
*   and "OID.1.2.840.10040.4.1".
*
* - MD5 is the message digest scheme described in RFC 1321.
*   There are no aliases for MD5.
*/

public final class Sun extends Provider {

    private static final String INFO = "SUN " + 
    "(DSA key/parameter generation; DSA signing; " +
    "SHA-1, MD5 digests; SecureRandom; X.509 certificates; JKS keystore)";

    public Sun() {
	/* We are the SUN provider */
	super("SUN", 1.2, INFO);

	AccessController.doPrivileged(new java.security.PrivilegedAction() {
	    public Object run() {

		/*
		* Signature engines 
		*/
		put("Signature.SHA1withDSA", "sun.security.provider.DSA");
	    
		put("Alg.Alias.Signature.DSA", "SHA1withDSA");
		put("Alg.Alias.Signature.DSS", "SHA1withDSA");
		put("Alg.Alias.Signature.SHA/DSA", "SHA1withDSA");
		put("Alg.Alias.Signature.SHA-1/DSA", "SHA1withDSA");
		put("Alg.Alias.Signature.SHA1/DSA", "SHA1withDSA");
		put("Alg.Alias.Signature.SHAwithDSA", "SHA1withDSA");
		put("Alg.Alias.Signature.DSAWithSHA1", "SHA1withDSA");
		put("Alg.Alias.Signature.OID.1.3.14.3.2.13", "SHA1withDSA");
		put("Alg.Alias.Signature.OID.1.3.14.3.2.27", "SHA1withDSA");
		put("Alg.Alias.Signature.OID.1.2.840.10040.4.3",
		    "SHA1withDSA");
		put("Alg.Alias.Signature.1.3.14.3.2.13", "SHA1withDSA");
		put("Alg.Alias.Signature.1.3.14.3.2.27", "SHA1withDSA");
		put("Alg.Alias.Signature.1.2.840.10040.4.3", "SHA1withDSA");
	    
		/*
		*  Key Pair Generator engines 
		*/
		put("KeyPairGenerator.DSA", 
		    "sun.security.provider.DSAKeyPairGenerator");

		put("Alg.Alias.KeyPairGenerator.OID.1.3.14.3.2.12", "DSA");
		put("Alg.Alias.KeyPairGenerator.OID.1.2.840.10040.4.1", "DSA");
		// the following are not according to our formal spec but
		// are still supported
		put("Alg.Alias.KeyPairGenerator.1.3.14.3.2.12", "DSA");
		put("Alg.Alias.KeyPairGenerator.1.2.840.10040.4.1", "DSA");
		
		/* 
		* Digest engines 
		*/
		put("MessageDigest.MD5", "sun.security.provider.MD5");
		put("MessageDigest.SHA", "sun.security.provider.SHA");
		
		put("Alg.Alias.MessageDigest.SHA-1", "SHA");
		put("Alg.Alias.MessageDigest.SHA1", "SHA");

		/*
		* Algorithm Parameter Generator engines
		*/
		put("AlgorithmParameterGenerator.DSA",
		    "sun.security.provider.DSAParameterGenerator");
		
		/*
		* Algorithm Parameter engines
		*/
		put("AlgorithmParameters.DSA",
		    "sun.security.provider.DSAParameters");
		put("Alg.Alias.AlgorithmParameters.1.3.14.3.2.12", "DSA");
		put("Alg.Alias.AlgorithmParameters.1.2.840.10040.4.1", "DSA");

		/*
		* Key factories
		*/
		put("KeyFactory.DSA", "sun.security.provider.DSAKeyFactory");
		put("Alg.Alias.KeyFactory.1.3.14.3.2.12", "DSA");
		put("Alg.Alias.KeyFactory.1.2.840.10040.4.1", "DSA");
		
		/*
		* SecureRandom
		*/
		put("SecureRandom.SHA1PRNG",
		    "sun.security.provider.SecureRandom");
		
		/*
		* Certificates
		*/
		put("CertificateFactory.X509",
		    "sun.security.provider.X509Factory");
		put("Alg.Alias.CertificateFactory.X.509", "X509");
		
		/*
		* KeyStore
		*/
		put("KeyStore.JKS", "sun.security.provider.JavaKeyStore");
		
		return null;
	    }
	});
    }
}

Appendix B: The java.security Properties File

Below is a copy of the java.security file that appears in every JDK installation. This file appears in the lib/security (lib\security on Windows) directory of the JDK. Thus, if the JDK is installed in a directory called jdk1.2, the file would be

See Step 5 for an example of adding information about your provider to this file. 
#
# This is the "master security properties file".
#
# In this file, various security properties are set for use by
# java.security classes. This is where users can statically register 
# Cryptography Package Providers ("providers" for short). The term 
# "provider" refers to a package or set of packages that supply a 
# concrete implementation of a subset of the cryptography aspects of 
# the Java Security API. A provider may, for example, implement one or 
# more digital signature algorithms or message digest algorithms.
#
# Each provider must implement a subclass of the Provider class.
# To register a provider in this master security properties file, 
# specify the Provider subclass name and priority in the format
#
#    security.provider.n=className 
#
# 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.
#
# className must specify the subclass of the Provider class whose 
# constructor sets the values of various properties that are required
# for the Java Security API to look up the algorithms or other 
# facilities implemented by the provider.
# 
# There must be at least one provider specification in java.security. 
# There is a default provider that comes standard with the JDK. It
# is called the "SUN" provider, and its Provider subclass
# named Sun appears in the sun.security.provider package. Thus, the
# "SUN" provider is registered via the following:
#
#    security.provider.1=sun.security.provider.Sun 
#
# (The number 1 is used for the default provider.) 
#
# Note: Statically registered Provider subclasses are instantiated 
# when the system is initialized. Providers can be dynamically 
# registered instead by calls to either the addProvider or 
# insertProviderAt method in the Security class.

#
# List of providers and their preference orders (see above):
#
security.provider.1=sun.security.provider.Sun

#
# Class to instantiate as the system Policy. This is the name of the class
# that will be used as the Policy object.
#
policy.provider=sun.security.provider.PolicyFile

# The default is to have a single system-wide policy file, 
# and a policy file in the user's home directory.
policy.url.1=file:${java.home}/lib/security/java.policy
policy.url.2=file:${user.home}/.java.policy

# whether or not we expand properties in the policy file
# if this is set to false, properties (${...}) will not be expanded in policy
# files.
policy.expandProperties=true

# whether or not we allow an extra policy to be passed on the command line
# with -Djava.security.policy=somefile. Comment out this line to disable
# this feature.
policy.allowSystemProperty=true

# whether or not we look into the IdentityScope for trusted Identities
# when encountering a 1.1 signed JAR file. If the identity is found
# and is trusted, we grant it AllPermission.
policy.ignoreIdentityScope=false

#
# Default keystore type.
#
keystore.type=jks

#
# Class to instantiate as the system scope:
#
system.scope=sun.security.provider.IdentityDatabase

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