# How to Implement a Provider for the JavaTM Cryptography Extension

## in the JavaTM 2 Platform Standard Edition Development Kit (JDK) 5.0

  Introduction
    Who Should Read This Document
    Related Documentation
    A Note on Terminology
  What's New
  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
    Step 6: Write and Compile Test Programs
    Step 7: Run your Test Programs
    Step 8: Apply for U.S. Government Export Approval If Required
    Step 9: Document your Provider and its Supported Services
    Step 10: Make Your Provider Software and Documentation Available to Clients
  How a Provider Can Do Self-Integrity Checking
  Further Implementation Details and Requirements
    Algorithm Aliases
    Service Interdependencies
    Default Initializations
    Diffie-Hellman Interfaces and their Required Implementations
    Algorithm Parameter Specification Classes
    Key Specification Classes Required by Key Factories
    Secret-Key Generation
    Ensuring Exportablity
  Appendix A: The "SunJCE" Provider's Master Class

# Introduction

> 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 now been integrated into the Java 2 SDK, v 1.4.

> JCE is based on the same design principles found elsewhere in the Java Cryptography Architecture framework utilized by all the cryptography-related security components of the Java 2 platform: implementation independence and, whenever possible, algorithm independence. It uses the same "provider" architecture, which uses the notion of a Cryptographic Service 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.

> JCE extends the list of cryptographic services of which a provider can supply implementations. A provider could, for example, contain an implementation of one or more digital signature algorithms and one or more cipher algorithms.

> A program wishing to use cryptography functionality may simply request a particular type of object (such as a Cipher object) implementing a particular algorithm (such as DES) 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 algorithm desired.

> Each Java 2 SDK installation has one or more provider packages installed. Each provider package supplies implementations of cryptographic services defined in one or more security components of the Java 2 SDK (including JCE).

> 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.

> The Java 2 SDK, v 1.4 release comes standard with a JCE provider named "SunJCE", which comes pre-installed and registered and which supplies the following cryptographic services:

> - An implementation of the DES (FIPS PUB 46-1), Triple DES, and Blowfish encryption algorithms in the Electronic Code Book (ECB), Cipher Block Chaining (CBC), Cipher Feedback (CFB), Output Feedback (OFB), and Propagating Cipher Block Chaining (PCBC) modes. (Note: Throughout this document, the terms "Triple DES" and "DES-EDE" will be used interchangeably.)

> - Key generators for generating keys suitable for the DES, Triple DES, Blowfish, HMAC-MD5, and HMAC-SHA1 algorithms.

> - An implementation of the MD5 with DES-CBC password-based encryption (PBE) algorithm defined in PKCS #5.

> - "Secret-key factories" providing bi-directional conversions between opaque DES, Triple DES and PBE key objects and transparent representations of their underlying key material.

> - An implementation of the Diffie-Hellman key agreement algorithm between two or more parties.

> - A Diffie-Hellman key pair generator for generating a pair of public and private values suitable for the Diffie-Hellman algorithm.

> - A Diffie-Hellman algorithm parameter generator.

> - A Diffie-Hellman "key factory" providing bi-directional conversions between opaque Diffie-Hellman key objects and transparent representations of their underlying key material.

> - Algorithm parameter managers for Diffie-Hellman, DES, Triple DES, Blowfish, and PBE parameters.

> - An implementation of the HMAC-MD5 and HMAC-SHA1 keyed-hashing algorithms defined in RFC 2104.

> - An implementation of the padding scheme described in PKCS#5.

> - A keystore implementation for the proprietary keystore type named "JCEKS".

> 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

> 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.

> This document is intended for developers of cryptographic service providers. 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.

> Only providers signed by a trusted entity can be plugged into the JCE framework.

> ## Related Documentation

> This document assumes you have already read the following documents:

> - Java Cryptography Architecture API Specification and Reference,
> - How to Implement a Provider for the Java Cryptography Architecture, and
> - JavaTM Cryptography Extension (JCE) Reference Guide for the JavaTM 2 SDK, Standard Edition, v 1.4.

> 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 these packages:

> - `java.security`
> - `java.security.spec`
> - `java.security.interfaces`
> - `javax.crypto`
> - `javax.crypto.spec`
> - `javax.crypto.interfaces`

> ## A Note on Terminology

> The JCE within the Java 2 SDK, v 1.4 includes two software components:

> - the framework that defines and supports cryptographic services that providers can supply implementations for. This framework includes everything in the `javax.crypto` package.

> - a provider named "SunJCE"
> Throughout this document, the term "JCE" by itself refers to the JCE framework in the Java 2 SDK, v 1.4. Whenever the JCE provider supplied with the Java 2 SDK, v 1.4 is mentioned, it will be referred to explicitly as the "SunJCE" provider.

# What's New in JCE

> Please refer to the What's New in JCE in the JDK 5.0 in the JCE Reference Guide for the difference between v1.4 and 5.0.

> These are the differences between JCE 1.2.1 and the JCE in the Java 2 SDK, v 1.4 that affect providers:

> - JCE Is Now in Java 2 SDK

> - Strong Cryptography Is the Default, Unlimited Is Available

> - Provider Authentication of JCE Framework No Longer Required

> ### JCE Is Now in Java 2 SDK

> > 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 now been integrated into the Java 2 SDK, v 1.4. The SunJCE provider is also included and is automatically registered in the `java.security` security properties file included with the Java 2 SDK, v 1.4.

> ### Strong Cryptography Is the Default, Unlimited Is Available

> > Due to import control restrictions, the jurisdiction policy files shipped with the Java 2 SDK, v 1.4 allow "strong" but limited cryptography to be used. An "unlimited" version of these files indicating no restrictions on cryptographic strengths is available for those living in eligible countries (which is most countries). You can download this version and replace the strong cryptography versions supplied with the Java 2 SDK, v 1.4 with the unlimited ones. See

> > > http://java.sun.com/products/jce/index-14.html

> > for information indicating where to go to download the unlimited version.

> > The jurisdiction policy files have been relocated to

> > >     <java-home>\lib\security         [Windows]
> > >     <java-home>/lib/security         [Solaris]

> > where `<java-home>` refers to the directory where the runtime software is installed, which is the top-level directory of the JavaTM 2 Runtime Environment (JRE) or the `jre` directory in the JavaTM 2 SDK (Java 2 SDK) software. They have been moved to this standard location so that it is easy to replace the strong cryptography versions that come with the Java 2 SDK, v 1.4 with the unlimited ones.

> ### Provider Authentication of JCE Framework No Longer Required

> > In JCE 1.2.1, providers needed to include code to authenticate the JCE framework to assure themselves of the integrity and authenticity of the JCE that they plugged into. Now that JCE is integrated into the Java 2 SDK, v 1.4, this is no longer necessary.

> > JCE 1.2.1 providers which follow the guidance in How to Implement a Provider for the Java Cryptography Extension 1.2.1 will continue to work with the JCE framework in the Java 2 SDK, v 1.4.

> > However, a provider whose framework authentication code locates the JCE framework via protection domain instead of following the recommendations in the aforementioned JCE 1.2.1 JCE provider document will not work in the Java 2 SDK, v 1.4. Now that JCE has been integrated into the Java 2 SDK, v 1.4, the JCE framework has a null code source just like any other class in the Java 2 SDK, v 1.4. You can either modify your provider to follow the recommended approach for authenticating the framework, or put in a conditional so that the framework authentication code is only executed when the provider is being run with JCE 1.2.1.

# Engine Classes and Corresponding SPI 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, and it either provides cryptographic operations (like those for ciphers or key agreement protocols), or generates or supplies the cryptographic material (keys or parameters) required for cryptographic operations. For example, two of the engine classes are the `Cipher` and `KeyAgreement` classes. The `Cipher` class provides access to the functionality of an encryption algorithm (such as DES), and the `KeyAgreement` class provides access to the functionality of a key agreement protocol (such as Diffie-Hellman).

> The Java Cryptography Architecture encompasses the classes of the J2SE 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.

> 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 now been integrated into the Java 2 SDK, v 1.4.

> JCE defines the following engine classes:

> - `Cipher`: used to encrypt or decrypt some specified data.

> - `KeyAgreement`: used to execute a key agreement (key exchange) protocol between 2 or more parties.

> - `KeyGenerator`: used to generate a secret (symmetric) key suitable for a specified algorithm.

> - `Mac`: used to compute the message authentication code of some specified data.

> - `SecretKeyFactory`: used to convert opaque cryptographic keys of type `SecretKey` into key specifications (transparent representations of the underlying key material), and vice versa.

> - `ExemptionMechanism`: used to provide the functionality of an exemption mechanism such as key recovery, key weakening, key escrow, or any other (custom) exemption mechanism. Applications or applets that use an exemption mechanism may be granted stronger encryption capabilities than those which don't. However, please note that cryptographic restrictions are no longer required for most countries, and thus exemption mechanisms may only be useful in those few countries whose governments mandate restrictions.

> 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 `Cipher` engine class, for example, provides access to the functionality of a cipher algorithm. The actual implementation supplied in a `CipherSpi` subclass (see next paragraph) would be that for a specific kind of encryption algorithm, such as DES or Triple DES.

> 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 `Cipher` engine class is the `CipherSpi` 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 `KeyAgreement` class, which provides access to a key agreement (key exchange) algorithm. Its implementations, in `KeyAgreementSpi` subclasses, may be those of various key agreement algorithms such as Diffie-Hellman.

> As a final example, the `SecretKeyFactory` engine class supports the conversion from opaque secret keys to transparent key specifications, and vice versa. (See Key Specification Classes Required by Key Factories.) The actual implementation supplied in a `SecretKeyFactorySpi` subclass would be that for a specific type of secret keys, e.g., DES keys.

# Steps to Implement and Integrate a Provider

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

>   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
>     Step 5a: Get a Code-Signing Certificate
>     Step 5b: Place Your Provider in a JAR File
>     Step 5c: Sign Your Provider
>     Step 5d: Install the Provider
>     Step 5e: Set Provider Permissions
>   Step 6: Write and Compile Test Programs
>   Step 7: Run your Test Programs
>   Step 8: Apply for U.S. Government Export Approval If Required
>   Step 9: Document your Provider and its Supported Services
>   Step 10: Make Your Provider Software and Documentation Available to Clients

> ## 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.

> > Note that your provider may supply implementations of cryptographic services defined in one or more of the security components of the Java 2 SDK v 1.4, including JCE.

> > In JCE in the Java 2 SDK, v 1.4 (as in the previous JCE 1.2.1 release), you can supply cipher, key agreement and MAC algorithms, as well as secret-key factories, secret-key generation services, and exemption mechanism implementations.

> > For cryptographic services not defined in JCE (e.g., signatures and message digests), please refer to Java Cryptography Architecture API Specification and Reference.

> > For each cryptographic service in the Java 2 SDK (including JCE ones), you need to create a subclass of the appropriate SPI class. JCE defines the following engine classes: `CipherSpi`, `KeyAgreementSpi`, `KeyGeneratorSpi`, `MacSpi`, `SecretKeyFactorySpi`, and `ExemptionMechanismSpi`. (See Engine Classes and Corresponding SPI Classes in this document for information on the JCE and other cryptographic classes in the Java 2 SDK, v 1.4.)

> > 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.

> > ### Additional JCE Provider Requirements and Recommendations

> > > When instantiating a provider's implementation (class) of a JCE service, the JCE framework will determine the provider's codebase (JAR file) and verify its signature. In this way, JCE authenticates the provider and ensures that only providers signed by a trusted entity can be plugged into JCE. Thus, one requirement for JCE providers is that they must be signed, as described in later steps.

> > > In addition, each provider should perform self-integrity checking to ensure that the JAR file containing its code has not been manipulated in an attempt to invoke provider methods directly rather than through JCE. For further information, see How a Provider Can Do Self-Integrity Checking.

> > > In order for provider classes to become unusable if instantiated by an application directly, bypassing JCE, providers should implement the following:

> > > - All SPI implementation classes in a provider package should be declared `final` (so that they cannot be subclassed), and their (SPI) implementation methods should be declared `protected`.

> > > - All crypto-related helper classes in a provider package should have package-private scope, so that they cannot be accessed from outside the provider package.

> > > For providers that may be exported outside the U.S., `CipherSpi` implementations must include an implementation of the `engineGetKeySize` method which, given a `Key`, returns the key size. If there are restrictions on available cryptographic strength specified in jurisdiction policy files, each `Cipher` initialization method calls `engineGetKeySize` and then compares the result with the maximum allowable key size for the particular location and circumstances of the applet or application being run. If the key size is too large, the initialization method throws an exception.

> > > Additional optional features that providers may implement are

> > > - the `engineWrap` and `engineUnwrap` methods of `CipherSpi`. Wrapping a key enables secure transfer of the key from one place to another. Information about wrapping and unwrapping keys is provided in the Wrapping and Unwrapping Keys section of the Java Cryptography Extension (JCE) Reference Guide.

> > > - one or more exemption mechanisms. An exemption mechanism is something such as key recovery, key escrow, or key weakening which, if implemented and enforced, may enable reduced cryptographic restrictions for an application (or applet) that uses it. For information on the requirements for apps that utilize exemption mechanisms, see How to Make Applications "Exempt" from Cryptographic Restrictions in the Java Cryptography Extension (JCE) Reference Guide.

> ## 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 `java.security.Provider` class.

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

> > - call `super`, specifying the provider name (see Step 2), version number, and a string of information about the provider and algorithms it supports. For example:

> >           super("CryptoX", 1.0, "CryptoX provider v1.0, implementing " +
> >               "RSA encryption and key pair generation, and DES encryption.");

> > - set the values of various properties that are required for the Java Security API to look up the cryptographic services implemented by the provider. For each service implemented by the provider, there must be a property whose name is the type of service (`Cipher`, `KeyAgreement`, `KeyGenerator`, `Mac`, `SecretKeyFactory`, or `ExemptionMechanism`), followed by a period and the name of the algorithm to which the service applies. The property value must specify the fully qualified name of the class implementing the service.

> >   The list below shows the various types of properties that must be defined for the various types of JCE services, where the actual algorithm name is substitued for algName:

> >   - `Cipher.`algName
> >   - `KeyAgreement.`algName
> >   - `KeyGenerator.`algName
> >   - `Mac.`algName
> >   - `SecretKeyFactory.`algName
> >   - `ExemptionMechanism.`algName

> >   In all of these except `ExemptionMechanism` and `Cipher`, algName is the standard name of the algorithm.

> >   In the case of `ExemptionMechanism`, algName refers to the name of the exemption mechanism, which can be one of the following: `KeyRecovery`, `KeyEscrow`, or `KeyWeakening`. Case does not matter.

> >   In the case of `Cipher`, algName may actually represent a transformation, and may be composed of an algorithm name, a particular mode, and a padding scheme. (See Appendix A of the Java Cryptography Extension (JCE) Reference Guide for the standard algorithm names that should be used.)

> >   The value of each property must be the fully qualified name of the class implementing the specified algorithm. That is, it must be the package name followed by the class name, where the two are separated by a period.

> >   As an example, the "SunJCE" provider implements the Diffie-Hellman key agreement algorithm in a class named `DHKeyAgreement` in the `com.sun.crypto.provider` package. Its subclass of `Provider` (which is the `SunJCE` class in the `com.sun.crypto.provider` package) sets the `KeyAgreement.DiffieHellman` property to have the value `com.sun.crypto.provider.DHKeyAgreement` via the following:

> >           put("KeyAgreement.DiffieHellman",
> >                 "com.sun.crypto.provider.DHKeyAgreement")

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

> > As mentioned above, in the case of a `Cipher` property, algName may actually represent a transformation. A transformation is a string that describes the operation (or set of operations) to be performed by a `Cipher` object on some given input. A transformation always includes the name of a cryptographic algorithm (e.g., DES), and may be followed by a mode and a padding scheme.

> > A transformation is of the form:

> > - algorithm/mode/padding, or

> > - algorithm

> > (In the latter case, provider-specific default values for the mode and padding scheme are used). For example, the following is a valid transformation:

> >         Cipher c = Cipher.getInstance("DES/CBC/PKCS5Padding");

> > When requesting a block cipher in stream cipher mode (e.g., `DES` in `CFB` or `OFB` mode), a client may optionally specify the number of bits to be processed at a time, by appending this number to the mode name as shown in the following sample transformations:

> >         Cipher c1 = Cipher.getInstance("DES/CFB8/NoPadding");
> >         Cipher c2 = Cipher.getInstance("DES/OFB32/PKCS5Padding");

> > If a number does not follow a stream cipher mode, a provider-specific default is used. (For example, the "SunJCE" provider uses a default of 64 bits.)

> > A provider may supply a separate class for each combination of algorithm/mode/padding. Alternatively, a provider may decide to provide more generic classes representing sub-transformations corresponding to algorithm or algorithm/mode or algorithm//padding (note the double slashes); in this case the requested mode and/or padding are set automatically by the `getInstance` methods of `Cipher`, which invoke the `engineSetMode` and `engineSetPadding` methods of the provider's subclass of `CipherSpi`.

> > That is, a `Cipher` property in a provider master class may have one of the formats shown in the table below.

> > `Cipher` Property Format | Description
> > `Cipher.`algName | A provider's subclass of `CipherSpi` implements algName with pluggable mode and padding
> > `Cipher.`algName/mode | A provider's subclass of `CipherSpi` implements algName in the specified mode, with pluggable padding
> > `Cipher.`algName//padding | A provider's subclass of `CipherSpi` implements algName with the specified padding, with pluggable mode
> > `Cipher.`algName/mode/padding | A provider's subclass of `CipherSpi` implements algName with the specified mode and padding

> > (See Appendix A of the Java Cryptography Extension (JCE) Reference Guide for the standard algorithm names, modes, and padding schemes that should be used.)

> > For example, a provider may supply a subclass of `CipherSpi` that implements DES/ECB/PKCS5Padding, one that implements DES/CBC/PKCS5Padding, one that implements DES/CFB/PKCS5Padding, and yet another one that implements DES/OFB/PKCS5Padding. That provider would have the following `Cipher` properties in its master class:

> > -         Cipher.DES/ECB/PKCS5Padding

> > -         Cipher.DES/CBC/PKCS5Padding

> > -         Cipher.DES/CFB/PKCS5Padding

> > -         Cipher.DES/OFB/PKCS5Padding

> > Another provider may implement a class for each of the above modes (i.e., one class for ECB, one for CBC, one for CFB, and one for OFB), one class for PKCS5Padding, and a generic DES class that subclasses from `CipherSpi`. That provider would have the following `Cipher` properties in its master class:

> > -         Cipher.DES

> > The `getInstance` factory method of the `Cipher` engine class follows these rules in order to instantiate a provider's implementation of `CipherSpi` for a transformation of the form "algorithm":

> > 1. Check if the provider has registered a subclass of `CipherSpi` for the specified "algorithm".

> >    If the answer is YES, instantiate this class, for whose mode and padding scheme default values (as supplied by the provider) are used.

> >    If the answer is NO, throw a `NoSuchAlgorithmException` exception.

> > The `getInstance` factory method of the `Cipher` engine class follows these rules in order to instantiate a provider's implementation of `CipherSpi` for a transformation of the form "algorithm/mode/padding":

> > 1. Check if the provider has registered a subclass of `CipherSpi` for the specified "algorithm/mode/padding" transformation.

> >    If the answer is YES, instantiate it.

> >    If the answer is NO, go to the next step.

> > 2. Check if the provider has registered a subclass of `CipherSpi` for the sub-transformation "algorithm/mode".

> >    If the answer is YES, instantiate it, and call `engineSetPadding(padding)` on the new instance.

> >    If the answer is NO, go to the next step.

> > 3. Check if the provider has registered a subclass of `CipherSpi` for the sub-transformation "algorithm//padding" (note the double slashes).

> >    If the answer is YES, instantiate it, and call `engineSetMode(mode)` on the new instance.

> >    If the answer is NO, go to the next step.

> > 4. Check if the provider has registered a subclass of `CipherSpi` for the sub-transformation "algorithm".

> >    If the answer is YES, instantiate it, and call `engineSetMode(mode)` and `engineSetPadding(padding)` on the new instance.

> >    If the answer is NO, throw a `NoSuchAlgorithmException` exception.

> ## 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

> > ### Step 5a: Get a Code-Signing Certificate

> > > The next step is to request a code-signing certificate so that you can use it to sign your provider prior to testing. The certificate will be good for both testing and production. It will be valid for 5 years.

> > > Below are the steps you should use to get a code-signing certificate. For more information on the keytool tool, see keytool (for Solaris) (for Microsoft Windows).

> > > 1. Use keytool to generate a DSA keypair.

> > >          keytool -genkey -alias <alias> -keyalg DSA -keysize 1024
> > >            -dname "cn=<Company Name>,ou=Java Software Code Signing,
> > >            o=Sun Microsystems Inc"
> > >            -keystore <keystore file name>
> > >            -storepass <keystore password>

> > >    (Note: This must be typed as a single line. Multiple lines and indentation are used in the examples so that they are legible.)

> > >    This will generate a DSA keypair (a public key and an associated private key) and store it in an entry in the specified keystore. The public key is stored in a self-signed certificate. The keystore entry can subsequently be accessed using the specified alias.

> > >    The option values in angle brackets ("<" and ">") represent the actual values that must be supplied. For example, `<alias>` must be replaced with whatever alias name you wish to be used to refer to the newly-generated keystore entry in the future, and `<keystore file name>` must be replaced with the name of the keystore to be used. Note: Do not surround actual values with angle brackets. For example, if you want your alias to be `myTestAlias`, specify the `-alias` option as follows:

> > >            -alias myTestAlias

> > >    If you specify a keystore that doesn't yet exist, it will be created.

> > >    Note: If command lines you type are not allowed to be as long as the `keytool -genkey` command you want to execute (for example, if you are typing to a Microsoft Windows DOS prompt), you can create and execute a plain-text batch file containing the command. That is, create a new text file that contains nothing but the full `keytool -genkey` command. (Remember to type it all on one line.) Save the file with a .bat extension. Then in your DOS window, type the file name (with its path, if necessary). This will cause the command in the batch file to be executed.

> > > 2. Use keytool to generate a certificate signing request.

> > >    >     keytool -certreq -alias <alias> -sigalg DSA
> > >    >             -file <csr file name>
> > >    >             -keystore <keystore file name>
> > >    >             -storepass <keystore password>

> > >    Here, `<alias>` is the alias for the DSA keypair entry created in the previous step. This command generates a Certificate Signing Request (CSR), using the PKCS#10 format. It stores the CSR in the file whose name is specified in `<csr file name>`.

> > > 3. Send the CSR, contact information, and other required documentation to the JCE Code Signing Certification Authority.

> > >    Send, via email, the CSR and contact information (see below) to javasoft-cert-request@sun.com. Put the following in the Subject line of your email message:

> > >          Request a Certificate for Signing a JCE Provider

> > >    Put the contact information in the body of the message and send the CSR file as a plain text attachment to the message. If your mail tool has an option for specifying the encoding format to be used for attachments, select the "MIME" option. Note: The CSR file is just a plain text file, in Base 64 encoding. Only the first and last lines are human-readable.

> > >    Include the following contact information in the body of your message:

> > >    >     Company Name
> > >    >     Street Address (Not a post office box)
> > >    >     City
> > >    >     State/Province
> > >    >     Country
> > >    >     Company Telephone Number
> > >    >     Company Fax Number
> > >    >     Requester Name
> > >    >     Requester Telephone Number
> > >    >     Requester Email Address
> > >    >     Brief description of your company (size,
> > >    >         line of business, etc.)

> > >    All of the above information is required.

> > >    After the JCE Code Signing Certification Authority has received your email message, they will send you a request number via email. Once you receive this request number, you should print, fill out and mail the Certification Form for CSPs.

> > >    This form should be mailed to the address below. Be sure to include the request number on the form so that your hardcopy mailing can be matched to the email message containing your CSR and contact information.

> > >    > Sun Microsystems, Inc.
> > >    > International Trade Services/Export Compliance
> > >    > Attn: Encryption Export
> > >    > 4120 Network Circle MS: USCA12-204
> > >    > Santa Clara, CA 95054
> > >    > U.S.A.

> > >    After the JCE Code Signing Certification Authority has received both your email message and the required form, they will authenticate you, the requester. Then they will create and sign a code-signing certificate valid for 5 years. You will receive an email message containing two plain-text file attachments: one file containing this code-signing certificate and another file containing its own CA certificate, which authenticates its public key.

> > > 4. Use keytool to import the certificates received from the CA.

> > >    Once you have received the two certificates from the JCE Code Signing Certification Authority, you can use keytool to import them into your keystore.

> > >    First import the CA's certificate as a "trusted certificate":

> > >    >     keytool -import -alias <alias for the CA cert>
> > >    >             -file <CA cert file name>
> > >    >             -keystore <keystore file name>
> > >    >             -storepass <keystore password>

> > >    Then import the code-signing certificate:

> > >    >     keytool -import -alias <alias>
> > >    >             -file <code-signing cert file name>
> > >    >             -keystore <keystore file name>
> > >    >             -storepass <keystore password>

> > >    Here, `<alias>` is the same alias as that which you created in step 1 where you generated a DSA keypair. This command replaces the self-signed certificate in the keystore entry specified by `<alias>` with the one signed by the JCE Code Signing Certification Authority.

> > > Now that you have in your keystore a certificate from an entity trusted by JCE (the JCE Code Signing Certification Authority), you can place your provider code in a JAR file (Step 5b) and then use that certificate to sign the JAR file (Step 5c).

> > ### Step 5b: Place Your Provider in a JAR File

> > > Place your provider code in a JAR file, in preparation for signing it in the next step. For more information on the jar tool, see jar (for Solaris) (for Microsoft Windows).

> > >     jar cvf <JAR file name> <list of classes, separated by spaces>

> > > This command creates a JAR file with the specified name containing the specified classes.

> > ### Step 5c: Sign Your Provider

> > > Sign the JAR file created in the previous step with the code-signing certificate obtained in Step 5a. For more information on the jarsigner tool, see jarsigner (for Solaris) (for Microsoft Windows).

> > > >     jarsigner -keystore <keystore file name>
> > > >               -storepass <keystore password>
> > > >               <JAR file name> <alias>

> > > Here, `<alias>` is the alias into the keystore for the entry containing the code-signing certificate received from the JCE Code Signing Certification Authority (the same alias as that specified in the commands in Step 5a).

> > > You can test verification of the signature via the following:

> > > >     jarsigner -verify <JAR file name>

> > > The text "jar verified" will be displayed if the verification was successful.

> > ### Step 5d: 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.

> > > Installing a provider is done in two steps: 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) file. There are a two possible ways to install provider classes:
> > > > - Install the JAR file containing the provider classes as an "installed" or "bundled" extension.
> > > > - Place the JAR file containing the provider classes in your CLASSPATH.

> > > > The provider JAR file will be considered an installed extension if it is placed in the standard place for the JAR files of an installed extension:

> > > > >     <java-home>/lib/ext         [Solaris]
> > > > >     <java-home>\lib\ext         [Windows]

> > > > Here `<java-home>` refers to the directory where the runtime software is installed, which is the top-level directory of the JavaTM 2 Runtime Environment (JRE) or the `jre` directory in the JavaTM 2 SDK (Java 2 SDK) software. For example, if you have the Java 2 SDK, v 1.4 installed on Solaris in a directory named `/home/user1/J2SDK1.4.0`, or on Microsoft Windows in a directory named `C:\J2SDK1.4.0`, then you need to install the JAR file in the following directory:

> > > > >     /home/user1/J2SDK1.4.0/jre/lib/ext    [Solaris]
> > > > >     C:\J2SDK1.4.0\jre\lib\ext             [Windows]

> > > > Similarly, if you have the JRE, v 1.4 installed on Solaris in a directory named `/home/user1/j2re1.4.0`, or on Microsoft Windows in a directory named `C:\j2re1.4.0`, you need to install the JAR file in the following directory:

> > > > >     /home/user1/j2re1.4.0/lib/ext         [Solaris]
> > > > >     C:\j2re1.4.0\lib\ext                  [Windows]

> > > > For more information on "installed" extensions, see Installed Extensions.

> > > > For more information on "bundled" extensions, see Bundled Extensions.

> > > #### Configuring the Provider

> > > > The next step is to add the provider to your list of approved providers. This is done statically by editing the security properties file

> > > > >     <java-home>/lib/security/java.security     [Solaris]
> > > > >     <java-home>\lib\security\java.security     [Windows]

> > > > Here `<java-home>` refers to the directory where the JRE was installed. For example, if you have the Java 2 SDK v 1.4 installed on Solaris in a directory named `/home/user1/J2SDK1.4.0`, or on Microsoft indows in a directory named `C:\J2SDK1.4.0`, then you need to edit the following file:

> > > > >     /home/user1/J2SDK1.4.0/jre/lib/security/java.security  [Solaris]
> > > > >     C:\J2SDK1.4.0\jre\lib\security\java.security           [Windows]

> > > > Similarly, if you have the Java 2 Runtime Environment, v 1.4 installed on Solaris in a directory named `/home/user1/j2re1.4.0`, or on Windows in a directory named `C:\j2re1.4.0`, then you need to edit this file:

> > > > >     /home/user1/j2re1.4.0/lib/security/java.security       [Solaris]
> > > > >     C:\j2re1.4.0\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.

> > > > The Java 2 SDK, v 1.4 comes standard with a provider named "SUN", which is automatically configured as a static provider in the `java.security` properties file, as follows:

> > > > >     security.provider.1=sun.security.provider.Sun

> > > > (The "SUN" provider's master class is the `Sun` class in the `sun.security.provider` package.)

> > > > The JCE provider "SunJCE" and other security-related providers shipped with the Java 2 platform are also automatically configured as static providers.

> > > > To utilize another JCE provider, add a line registering the alternate provider, giving it whatever preference order you prefer (and making corresponding adjustments to the other providers' orders, if needed).

> > > > Suppose that your master class is the `CryptoX` class in the `com.cryptox.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, and increment the preference order numbers for all other providers whose numbers were greater than or equal to 2 before your addition:

> > > >         security.provider.2=com.cryptox.provider.CryptoX

> > > > Note: Providers may also be registered dynamically. To do so, a program (such as your test program, to be written in Step 6) 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 code which is granted the following permission:

> > > > >     java.security.SecurityPermission "insertProvider.{name}"

> > > > where `{name}` is replaced by the actual provider name. For example, if the provider name is "MyJCE" and if the provider's code is in the `myjce_provider.jar` file in the `/localWork` directory, then here is a sample policy file `grant` statement granting that permission:

> > > > >     grant codeBase "file:/localWork/myjce_provider.jar" {
> > > > >       permission java.security.SecurityPermission
> > > > >           "insertProvider.MyJCE";
> > > > >     };

> > ### Step 5e: Set Provider Permissions

> > > Whenever JCE providers are not installed extensions, permissions must be granted for when applets or applications using JCE are run while a security manager is installed. There is typically a security manager installed whenever an applet is running, and a security manager may be installed for an application either via code in the application itself or via a command-line argument. Permissions do not need to be granted to installed extensions, since the default system policy file grants all permissions to installed extensions.

> > > Whenever a client does not install your provider as an installed extension, your provider may need the following permissions granted to it in the client environment:

> > > - `java.lang.RuntimePermission` to get class protection domains. The provider may need to get its own protection domain in the process of doing self-integrity checking.
> > > - `java.security.SecurityPermission` to set provider properties.

> > > To ensure your provider works when a security manager is installed and the provider is not an installed extension, you need to test such an installation and execution environment. In addition, prior to testing you need to grant appropriate permissions to your provider and to any other providers it uses. For example, a sample statement granting permissions to a provider whose name is "MyJCE" and whose code is in `myjce_provider.jar` appears below. Such a statement could appear in a policy file. In this example, the `myjce_provider.jar` file is assumed to be in the `/localWork` directory.

> > > >     grant codeBase "file:/localWork/myjce_provider.jar" {
> > > >       permission java.lang.RuntimePermission "getProtectionDomain";
> > > >       permission java.security.SecurityPermission
> > > >           "putProviderProperty.MyJCE";
> > > >     };

> ## 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 encrypted.

> > 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 the DES encryption algorithm, you could check to ensure it's found when requested by using the following code (again substituting your provider name for "MyPro"):

> >         Cipher c = Cipher.getInstance("DES", "MyPro");

> >         System.out.println("My Cipher algorithm name is " + c.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.

> > If your provider implements an exemption mechanism, you should write a test applet or application that uses the exemption mechanism. Such an applet/application also needs to be signed, and needs to have a "permission policy file" bundled with it. See How to Make Applications "Exempt" from Cryptographic Restrictions in the Java Cryptography Extension (JCE) Reference Guide for complete information on creating and testing such an application.

> ## 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.

> > Be sure to include testing of your programs using different installation options (e.g. making the provider an installed extension or placing it on the class path) and execution environments (with or without a security manager running). Installation options are discussed in Step 5d. In particular, you need to ensure your provider works when a security manager is installed and the provider is not an installed extension -- and thus the provider must have permissions granted to it; therefore, you need to test such an installation and execution environment, after granting required permissions to your provider and to any other providers it uses, as described in Step 5e.

> > If you find during testing that your code needs modification, make the changes, recompile (Step 4), place the updated provider code in a JAR file (Step 5b), sign the JAR file (Step 5c), re-install the provider (Step 5d), if needed fix or add to the permissions (Step 5e), and then re-test your programs. Repeat these steps as needed.

> ## Step 8: Apply for U.S. Government Export Approval If Required

> > All U.S. vendors whose providers may be exported outside the U.S. should apply to the Bureau of Export Administration in the U.S. Department of Commerce for export approval. Please consult your export counsel for more information.

> > Note: If your provider calls `Cipher.getInstance()` and the returned `Cipher` object needs to perform strong cryptography regardless of what cryptographic strength is allowed by the user's downloaded jurisdiction policy files, you should include a copy of the `cryptoPerms` permission policy file which you intend to bundle in the JAR file for your provider and which specifies an appropriate permission for the required cryptographic strength. The necessity for this file is just like the requirement that applets and applications "exempt" from cryptographic restrictions must include a `cryptoPerms` permission policy file in their JAR file. For more information on the creation and inclusion of such a file, see How to Make Applications "Exempt" from Cryptographic Restrictions in the Java Cryptography Extension (JCE) Reference Guide.

> > Here are two URLs that may be useful:

> > - U.S. Department of Commerce: http://www.doc.gov

> > - Bureau of Export Administration: http://www.bxa.doc.gov

> ## Step 9: Document your Provider and its Supported Services

> > The next step is to write documentation for your clients. At the minimum, you need to specify:
> > - the name programs should use to refer to your provider. Note: As of this writing, provider name searches are case-sensitive. That is, if your master class specifies your provider name as "CryptoX" but a user requests "CRYPTOx", your provider will not be found. This behavior may change in the future, but for now be sure to warn your clients to use the exact case you specify.

> > - the types of algorithms and other services implemented by your provider.

> > - instructions for installing the provider, similar to those provided in Step 5d, except that the information and examples should be specific to your provider.

> > - the permissions your provider will require if it is not installed as an installed extension and if a security manager is run, as described in Step 5e.
> > In addition, your documentation should specify anything else of interest to clients, such as any default algorithm parameters.

> > #### MACs

> > For each MAC 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 "message authentication codes" (MACs) may be possible through cloning. Clients who do not know whether or not a MAC implementation is cloneable can find out by attempting to clone the `Mac` object and catching the potential exception, as illustrated by the following example:

> >     try {
> >         // try and clone it
> >         /* compute the MAC for i1 */
> >         mac.update(i1);
> >         byte[] i1Mac = mac.clone().doFinal();

> >         /* compute the MAC for i1 and i2 */
> >         mac.update(i2);
> >         byte[] i12Mac = mac.clone().doFinal();

> >         /* compute the MAC for i1, i2 and i3 */
> >         mac.update(i3);
> >         byte[] i123Mac = mac.doFinal();
> >     } catch (CloneNotSupportedException cnse) {
> >       // have to use an approach not involving cloning
> >     }

> > where
> > - `mac` is the MAC object they received when they requested one via a call to `Mac.getInstance`,

> > - `i1`, `i2` and `i3` are input byte arrays, and

> > - they want to calculate separate hashes for:
> >   - `i1`
> >   - `i1 and i2`
> >   - `i1, i2, and i3`

> > #### 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 Diffie-Hellman key pair generator supplied by the "SunJCE" provider uses a default prime modulus size (`keysize`) of 1024 bits.

> > #### Key Factories

> > A provider should document all the key specifications supported by its (secret-)key factory.

> > #### 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 "SunJCE" provider uses a default prime modulus size (`keysize`) of 1024 bits for the generation of Diffie-Hellman parameters.

> ## Step 10: Make your Provider Software and Documentation Available to Clients

> > The final step is to make your provider software and documentation available to your customers.

# How a Provider Can Do Self-Integrity Checking

> Each provider should do self-integrity checking to ensure that the JAR file containing its code has not been tampered with, for example in an attempt to invoke provider methods directly rather than through JCE. Providers that provide implementations for JCE services must be digitally signed and should be signed with a certificate issued by "trusted" Certification Authorities. Currently, the following two Certification Authorities are considered "trusted":
> - Sun Microsystems' JCE Code Signing CA, and
> - IBM JCE Code Signing CA.
> Please refer to Step 5b for detailed information on how to get a code-signing certificate from Sun Microsystems' JCE Code Signing CA and the certificate of that CA.

> After getting the signing certificate from above Certification Authority, provider packages should embed within themselves the bytes for its own signing certificate, for example in an array like the `bytesOfProviderCert` array referred to in the Identifying Each of the Signers and Determining If One is Trusted section below. At runtime, the embedded certificate will be used in determining whether or not the provider code is authentic.

> The basic approach a provider can use to check its own integrity is:

> 1. Determine the URL of the JAR file containing the provider code, and

> 2. Verify the JAR file's digital signatures to ensure that at least one signer of each entry of the JAR file is trusted.

> Each of these steps is described in the following sections:

> Finding the Provider JAR File: Basics
>   Determining the Provider's JAR File URL
>   Creating a JarFile Referring to the JAR File
> Verifying the Provider JAR File: Basics
>   Verification Setup
>   JAR File Signature Check
>   Verifying Signatures
>   Ensuring Signers Are Trusted
>     Getting the List of Certificates
>     Identifying Each of the Signers and Determining If One is Trusted
> Notes on the Sample Code

> > Note: The sample code `MyJCE.java` is a complete code example that implements these steps. You can download this code for your reference. The Notes on the Sample Code section traces how these concepts are implemented in the sample code.

> > IMPORTANT NOTE:

> > In JCE 1.2.1, providers needed to include code to authenticate the JCE framework to assure themselves of the integrity and authenticity of the JCE that they plugged into. Now that JCE is integrated into the Java 2 SDK, v 1.4, this is no longer necessary.

> > One implication is that a provider written just for JCE 1.2.1 will not work in the Java 2 SDK, v 1.4 because the provider's JCE framework authentication check will not work; the JCE framework code is no longer where the provider expects it to be. If you want your provider to work only with the Java 2 SDK, v 1.4, it should not have code to authenticate the JCE framework. On the other hand, if you want your provider to work both with JCE 1.2.1 and with the JCE in the Java 2 SDK, v 1.4, then add a conditional statement. This way the provider code to authenticate the JCE framework is executed only when the provider is run with JCE 1.2.1. The following is sample code:

> > >     Class cipherCls = Class.forName("javax.crypto.Cipher");
> > >     CodeSource cs =
> > >         cipherCls.getProtectionDomain().getCodeSource();
> > >     if (cs != null) {
> > >         // Authenticate JCE framework
> > >         . . .
> > >     }

> ## Finding the Provider JAR File: Basics

> > ### Determining the Provider's JAR File URL

> > > The URL for the provider's JAR file can be obtained by determining the provider's `CodeSource` and then calling the `getLocation` method on the `CodeSource`.

> > > >     URL providerURL = (URL) AccessController.doPrivileged(
> > > >                                 new PrivilegedAction) {
> > > >         public Object run() {
> > > >             CodeSource cs = MyJCE.class.getProtectionDomain().
> > > >                                         getCodeSource();
> > > >             return cs.getLocation();
> > > >         }
> > > >     });

> > ### Creating a JarFile Referring to the JAR File

> > > Once you have the URL for the provider's JAR file, you can create a `java.util.jar.JarFile` referring to the JAR file. This instance is needed in the step for verifying the Provider JAR file.

> > > To create the JAR file, first open a connection to the specified URL by calling its `openConnection` method. Since the URL is a JAR URL, the type is `java.net.JarURLConnection`. Here's the basic code:

> > > >     // Prep the url with the appropriate protocol.
> > > >     jarURL =
> > > >         url.getProtocol().equalsIgnoreCase("jar") ?
> > > >         url :
> > > >         new URL("jar:" + url.toString() + "!/");
> > > >     // Retrieve the jar file using JarURLConnection
> > > >     JarFile jf = (JarFile) AccessController.doPrivileged(
> > > >     	                 new PrivilegedExceptionAction() {
> > > >         public Object run() throws Exception {
> > > >             JarURLConnection conn =
> > > >                   (JarURLConnection) jarURL.openConnection();
> > > >             ...

> > > Now that you have a `JarURLConnection`, you can call its `getJarFile` method to get the JAR file:

> > > >     // Always get a fresh copy, so we don't have to
> > > >     // worry about the stale file handle when the
> > > >     // cached jar is closed by some other application.
> > > >     conn.setUseCaches(false);
> > > >     jf = conn.getJarFile();

> ## Verifying the Provider JAR File: Basics

> > Once you have determined the URL for your provider JAR file and you have created a `JarFile` referring to the JAR file, as shown in the steps above, you can then verify the file.

> > The basic approach is:

> > 1. Ensure that at least one of each entry's signer's certificates is equal to the provider's own code signing certificate.

> > 2. Go through all the entries in the JAR file and ensure the signature on each one verifies correctly.

> > 3. Ensure that at least one of each entry's signer's certificates can be traced back to a trusted Certification Authority.

> > Sample code for each of these steps is presented and described in the following sections:

> > Verification Setup
> > JAR File Signature Check
> > Verifying Signatures
> > Ensuring Signers Are Trusted
> >   Getting the List of Certificates
> >   Identifying Each of the Signers and Determining If One is Trusted

> > ### Verification Setup

> > Our approach is to define a class `JarVerifier` to handle the retrieval of a JAR file from a given URL and verify whether the JAR file is signed with the specified certificate.

> > The constructor of `JarVerifier` takes the provider URL as a parameter which will be used to retrieve the JAR file later.

> > The actual jar verification is implemented in the `verify` method which takes the provider code signing certificate as a parameter.

> > >     public void verify(X509Certificate targetCert)
> > >     	 throws IOException {
> > >         // variable 'jarFile' is a JarFile object created
> > >         // from the provider's Jar URL.
> > >         ...
> > >         Vector entriesVec = new Vector();

> > Basically the `verify` method will go through the JAR file entries twice: the first time checking the signature on each entry and the second time verifying the signer is trusted.

> > Note: In our code snippets the `jarFile` variable is the `JarFile` object of the provider's jar file.

> > ### JAR File Signature Check

> > An authentic provider JAR file is signed. So the JAR file has been tampered with if it isn't signed:

> > >     // Ensure the jar file is signed.
> > >     Manifest man = jarFile.getManifest();
> > >     if (man == null) {
> > >         throw new SecurityException("The provider is not signed");
> > >     }

> > ### Verifying Signatures

> > The next step is to go through all the entries in the JAR file and ensure the signature on each one verifies correctly. One possible way to verify the signature on a JAR file entry is to simply read the file. If a JAR file is signed, the `read` method itself automatically performs the signature verification. Here is sample code:

> > >     // Ensure all the entries' signatures verify correctly
> > >     byte[] buffer = new byte[8192];
> > >     Enumeration entries = jarFile.entries();

> > >     while (entries.hasMoreElements()) {
> > >         JarEntry je = (JarEntry) entries.nextElement();

> > >         // Skip directories.
> > >         if (je.isDirectory()) continue;
> > >         entriesVec.addElement(je);
> > >         InputStream is = jarFile.getInputStream(je);

> > >         // Read in each jar entry. A security exception will
> > >         // be thrown if a signature/digest check fails.
> > >         int n;
> > >         while ((n = is.read(buffer, 0, buffer.length)) != -1) {
> > >             // Don't care
> > >         }
> > >         is.close();
> > >     }

> > ### Ensuring Signers Are Trusted

> > The code in the previous section verified the signatures of all the provider JAR file entries. The fact that they all verify correctly is a requirement, but it is not sufficient to verify the authenticity of the JAR file. A final requirement is that the signatures were generated by the same entity as the one that developed this provider. To test that the signatures are trusted, we can again go through each entry in the JAR file (this time using the `entriesVec` built in the previous step), and for each entry that must be signed (that is, each entry that is not a directory and that is not in the META-INF directory):

> > 1. Get the list of signer certificates for the entry.
> > 2. Identify each of the certificate chains and determine whether any of the certificate chains are trusted. At least one of the certificate chains must be trusted.
> > The loop setup is the following:

> > >     Enumeration e = entriesVec.elements();
> > >     while (e.hasMoreElements()) {
> > >         JarEntry je = (JarEntry) e.nextElement();
> > >         ...
> > >     }

> > > #### Getting the List of Certificates

> > > The certificates for the signers of a JAR file entry `JarEntry` can be obtained simply by calling the `JarEntry` `getCertificates` method:

> > > >     Certificate[] certs = je.getCertificates();

> > > Adding this line of code to the previous loop setup code, and adding code to ignore directories and files in the META-INF directory gives us:

> > > >     while (e.hasMoreElements()) {
> > > >         JarEntry je = (JarEntry) e.nextElement();

> > > >         // Every file must be signed except files in META-INF.
> > > >         Certificate[] certs = je.getCertificates();
> > > >         if ((certs == null) || (certs.length == 0)) {
> > > >             if (!je.getName().startsWith("META-INF"))
> > > >                 throw new SecurityException("The provider " +
> > > >                                             "has unsigned " +
> > > >                                             "class files.");
> > > >             } else {
> > > >                 // Check whether the file is signed by the expected
> > > >                 // signer. The jar may be signed by multiple signers.
> > > >                 // See if one of the signers is 'targetCert'.
> > > >                 ...
> > > >             }
> > > >        ...

> > > #### Identifying Each of the Signers and Determining If One is Trusted

> > > The certificate array returned by the `JarEntry` `getCertificates` method contains one or more certificate chains. There is one chain per signer of the entry. Each chain contains one or more certificates. Each certificate in a chain authenticates the public key in the previous certificate.

> > > The first certificate in a chain is the signer's certificate which contains the public key corresponding to the private key actually used to sign the entry. Each subsequent certificate is a certificate for the issuer of the previous certificate. Since the self-integrity check is based on whether the JAR file is signed with the provider's signing cert, the trust decision will be made upon only the first certificate, the signer's certificate.

> > > We need to go through the array of certificate chains and check each chain and the associated signers until we find a trusted entity. For each JAR file entry, at least one of the signers must be trusted. A signer is considered "trusted" if and only if its certificate is equals to the embedded provider signing certificate.

> > > The following sample code loops through all the certificate chains, compares the first certificate in a chain to the embedded provider signing certificate, and only returns `true` if a match is found.

> > > >     int startIndex = 0;
> > > >     X509Certificate[] certChain;
> > > >     boolean signedAsExpected = false;

> > > >     while ((certChain = getAChain(certs, startIndex)) != null) {
> > > >         if (certChain[0].equals(targetCert)) {
> > > >             // Stop since one trusted signer is found.
> > > >             signedAsExpected = true;
> > > >             break;
> > > >         }
> > > >         // Proceed to the next chain.
> > > >         startIndex += certChain.length;
> > > >     }

> > > >     if (!signedAsExpected) {
> > > >         throw new SecurityException("The provider " +
> > > >                                     "is not signed by a " +
> > > >                                     "trusted signer");
> > > >     }

> > > The `getAChain` method is defined as follows:

> > > >     /**
> > > >      * Extracts ONE certificate chain from the specified certificate array
> > > >      * which may contain multiple certificate chains, starting from index
> > > >      * 'startIndex'.
> > > >     */
> > > >     private static X509Certificate[] getAChain(Certificate[] certs,
> > > >     					   int startIndex) {
> > > >         if (startIndex > certs.length - 1)
> > > >             return null;

> > > >         int i;
> > > >         // Keep going until the next certificate is not the
> > > >         // issuer of this certificate.
> > > >         for (i = startIndex; i < certs.length - 1; i++) {
> > > >             if (!((X509Certificate)certs[i + 1]).getSubjectDN().
> > > >                    equals(((X509Certificate)certs[i]).getIssuerDN())) {
> > > >                 break;
> > > >             }
> > > >         }

> > > >         // Construct and return the found certificate chain.
> > > >         int certChainSize = (i-startIndex) + 1;
> > > >         X509Certificate[] ret = new X509Certificate[certChainSize];
> > > >         for (int j = 0; j < certChainSize; j++ ) {
> > > >             ret[j] = (X509Certificate) certs[startIndex + j];
> > > >         }
> > > >         return ret;
> > > >     }

> ## Notes on the Sample Code

> > The sample code, `MyJCE.java`, is a sample provider which has a method `selfIntegrityChecking` which performs self-integrity checking. It first determines the URL of its own provider JAR file and then verifies that the provider JAR file is signed with the embedded code-signing certificate.

> > Note: The method `selfIntegrityChecking` should be called by all the constructors of its cryptographic engine classes to ensure that its integrity is not compromised.

> > Provider `MyJCE` performs self-integrity checking in the following steps:

> > 1. Determine the URL to access the provider JAR file using its own class, `MyJCE.class`.

> > 2. Instantiate a `JarVerifier` object with the provider URL in Step 1.

> > 3. Create a `X509Certificate` object from the embedded byte array `bytesOfProviderCert`.

> > 4. Call the `JarVerifier.verify` method to verify all entries in the provider JAR file are signed and are signed with the same certificate instantiated in Step 3.
> > Note: The class `JarVerifier` will retrieve the JAR file from the given URL, make sure the JAR file is signed, all entries have valid signatures, and that entries are signed with the specified `X509Certificate`.

> > A security exception is thrown by `JarVerifier.verify` in several cases:

> > - The certificate passed to `verify` is null (invalid).
> > - When unable to retrieve JAR file from the given URL.
> > - The provider is not signed. (The jar has no manifest.)
> > - The provider has unsigned class files.
> > - The provider is not signed with the specified certificate.

> > The `MyJCE.java` sample code is comprised of the code snippets shown above. In addition, it includes error handling, sample code signing certificate bytes, and code for instantiating a `X509Certificate` object from the embedded sample code signing certificate bytes.

> > Regarding the use of `AccessController.doPrivileged`, please see API For Privileged Blocks for information on the use of `doPrivileged`.

# Further Implementation Details and Requirements

> ## Algorithm Aliases

> > For many cryptographic algorithms, there is a single official "standard name." The standard names defined by JCE in the Java 2 SDK, v 1.4 are listed in Appendix A of the Java Cryptography Extension (JCE) Reference Guide.

> > For example, `DiffieHellman` is the standard name for the Diffie-Hellman key agreement algorithm defined in PKCS #3.

> > JCE uses the same aliasing scheme for algorithm names as the rest of the security products in the Java 2 SDK, v 1.4. That scheme enables clients to use aliases when referring to algorithms, rather than their standard names. For example, the "SunJCE" provider's master class (`SunJCE.java`) defines the alias "DH" for the key agreement whose standard name is `DiffieHellman`. Thus, the following statements are equivalent:

> >         KeyAgreement ka = KeyAgreement.getInstance("DiffieHellman", "SunJCE");

> >         KeyAgreement ka = KeyAgreement.getInstance("DH", "SunJCE");

> > 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 either `Cipher`, `KeyAgreement`, `KeyGenerator`, `Mac`, `SecretKeyFactory`, or `ExemptionMechanism`, and `aliasName` is your alias name. For all but `ExemptionMechanism`, the value of the property must be the standard algorithm name for the algorithm being aliased. For `ExemptionMechanism`, the value is the exemption mechanism name (`KeyRecovery`, `KeyEscrow`, or `KeyWeakening`).

> > As an example, the "SunJCE" provider defines the alias "DH" for the key agreement algorithm whose standard name is "DiffieHellman" by setting a property named `Alg.Alias.KeyAgreement.DH` to have the value `DiffieHellman` via the following:

> >         put("Alg.Alias.KeyAgreement.DH", "DiffieHellman");

> > Note that aliases defined by one provider are available only to that provider and not to any other providers. Thus, aliases defined by the "SunJCE" provider are available only to the "SunJCE" provider.

> ## Service Interdependencies

> > Some algorithms require the use of other types of algorithms. For example, a PBE algorithm usually needs to use a message digest algorithm in order to transform a password into a key.

> > 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 Java 2 Platform installation. For example, if you are implementing a PBE 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.

> ## 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 "SunJCE" provider uses a default modulus size (keysize) of 1024 bits for the generation of Diffie-Hellman parameters.

> ## Diffie-Hellman Interfaces and their Required Implementations

> > JCE contains the following interfaces (in the `javax.crypto.interfaces` package) for the convenience of programmers implementing Diffie-Hellman services:
> > - `DHKey`
> > - `DHPrivateKey`
> > - `DHPublicKey`
> > The following sections discuss requirements for implementations of these interfaces.

> > #### `DHPrivateKey` and `DHPublicKey` Implementations

> > > If you implement a Diffie-Hellman key pair generator or key factory, you need to create classes implementing the `DHPrivateKey` and `DHPublicKey` interfaces.

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

> > > If you implement a Diffie-Hellman key factory, your `engineGeneratePrivate` method (in your `KeyFactorySpi` subclass) will return an instance of your `DHPrivateKey` implementation, and your `engineGeneratePublic` method will return an instance of your `DHPublicKey` implementation.

> > > Also, your `engineGetKeySpec` and `engineTranslateKey` methods will expect the passed-in key to be an instance of a `DHPrivateKey` or `DHPublicKey` implementation. The `getParams` method provided by the interface implementations is useful for obtaining and extracting the parameters from the keys. You can then use the parameters, for example, as parameters to the `DHParameterSpec` constructor called to create a parameter specification from parameter values used to initialize a `KeyPairGenerator` object for Diffie-Hellman.

> > > If you implement the Diffie-Hellman key agreement algorithm, your `engineInit` method (in your `KeyAgreementSpi` subclass) will expect to be passed a `DHPrivateKey` and your `engineDoPhase` method will expect to be passed a `DHPublicKey`.

> > > Note: The `DHPublicKey` and `DHPrivateKey` interfaces define a very generic, provider-independent interface to Diffie-Hellman 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 `DHPrivateKey` or `DHPublicKey`, e.g., to take advantage of provider-specific implementation details. The same is true for the Diffie-Hellman algorithm `engineInit` and `engineDoPhase` methods (in your `KeyAgreementSpi` subclass).

> > > To see what methods need to be implemented by classes that implement the `DHPublicKey` and `DHPrivateKey` interfaces, first note the following interface signatures:

> > > In the `javax.crypto.interfaces` package:

> > > >     public interface DHPrivateKey extends DHKey,
> > > >                                      java.security.PrivateKey

> > > >     public interface DHPublicKey extends DHKey,
> > > >                                      java.security.PublicKey

> > > >     public interface DHKey

> > > In the `java.security` package:

> > > >     public interface PrivateKey extends Key

> > > >     public interface PublicKey extends Key

> > > >     public interface Key extends java.io.Serializable

> > > To implement the `DHPrivateKey` and `DHPublicKey` 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 `DHPrivateKey` interface.
> > > - the `getParams` method from the javax.crypto.interfaces.DHKey interface, since `DHPrivateKey` extends `DHKey`.
> > > - the `getAlgorithm`, `getEncoded`, and `getFormat` methods from the java.security.Key interface, since `DHPrivateKey` extends `java.security.PrivateKey`, and `PrivateKey` extends `Key`.
> > > Similarly, for public Diffie-Hellman keys, you need to supply a class that implements:
> > > - the `getY` method from the `DHPublicKey` interface.
> > > - the `getParams` method from the `javax.crypto.interfaces.DHKey` interface, since `DHPublicKey` extends `DHKey`.
> > > - the `getAlgorithm`, `getEncoded`, and `getFormat` methods from the java.security.Key interface, since `DHPublicKey` extends `java.security.PublicKey`, and `PublicKey` extends `Key`.

> ## Algorithm Parameter Specification 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., `DHParameterSpec` defines `getP`, `getG`, and `getL` methods, to access the p, g, and l 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.

> > JCE contains a number of `AlgorithmParameterSpec` implementations for the most frequently used cipher and key agreement algorithm parameters. If you are operating on algorithm parameters that should be for a different type of algorithm not provided by JCE, you will need to supply your own `AlgorithmParameterSpec` implementation appropriate for that type of algorithm.

> > JCE defines the following algorithm parameter specification classes in the `javax.crypto.spec` package:

> > ### The `IvParameterSpec` Class

> > > This class (which implements the `AlgorithmParameterSpec` interface) specifies the initialization vector (IV) used with a cipher in feedback mode.

> > > Method in `IvParameterSpec`
> > > | Method | Description
> > > `byte[] getIV()` | Returns the initialization vector (IV).

> > ### The `PBEParameterSpec` Class

> > > This class (which implements the `AlgorithmParameterSpec` interface) specifies the set of parameters used with a password-based encryption (PBE) algorithm.

> > > Methods in `PBEParameterSpec`
> > > | Method | Description
> > > `int getIterationCount()` | Returns the iteration count.
> > > `byte[] getSalt()` | Returns the salt.

> > ### The `RC2ParameterSpec` Class

> > > This class (which implements the `AlgorithmParameterSpec` interface) specifies the set of parameters used with the RC2 algorithm.

> > > Methods in `RC2ParameterSpec`
> > > | Method | Description
> > > `boolean equals(Object obj)` | Tests for equality between the specified object and this object.
> > > `int getEffectiveKeyBits()` | Returns the effective key size in bits.
> > > `byte[] getIV()` | Returns the IV or null if this parameter set does not contain an IV.
> > > `int hashCode()` | Calculates a hash code value for the object.

> > ### The `RC5ParameterSpec` Class

> > > This class (which implements the `AlgorithmParameterSpec` interface) specifies the set of parameters used with the RC5 algorithm.

> > > Methods in `RC5ParameterSpec`
> > > | Method | Description
> > > `boolean equals(Object obj)` | Tests for equality between the specified object and this object.
> > > `byte[] getIV()` | Returns the IV or null if this parameter set does not contain an IV.
> > > `int getRounds()` | Returns the number of rounds.
> > > `int getVersion()` | Returns the version.
> > > `int getWordSize()` | Returns the word size in bits.
> > > `int hashCode()` | Calculates a hash code value for the object.

> > ### The `DHParameterSpec` Class

> > > This class (which implements the `AlgorithmParameterSpec` interface) specifies the set of parameters used with the Diffie-Hellman algorithm.

> > > Methods in `DHParameterSpec`
> > > | Method | Description
> > > `BigInteger getG()` | Returns the base generator `g`.
> > > `int getL()` | Returns the size in bits, `l`, of the random exponent (private value).
> > > `BigInteger getP()` | Returns the prime modulus `p`.

> > > Many types of Diffie-Hellman services will find this class useful; for example, it is used by the Diffie-Hellman key agreement, key pair generator, algorithm parameter generator, and algorithm parameters classes implemented by the "SunJCE" provider. As a specific example, an algorithm parameters implementation must include an implementation for the `getParameterSpec` method, which returns an `AlgorithmParameterSpec`. The Diffie-Hellman algorithm parameters implementation supplied by "SunJCE" returns an instance of the `DHParameterSpec` class.

> ## Key Specification Classes Required by Key Factories

> > Key specifications are transparent representations of the key material that constitutes a key. JCE defines the following key specification classes in the `javax.crypto.spec` package: `DHPrivateKeySpec`, `DHPublicKeySpec`, `DESKeySpec`, `DESedeKeySpec`, `PBEKeySpec`, and `SecretKeySpec`.

> > ### The `DHPrivateKeySpec` Class

> > > This class (which implements the `KeySpec` interface) specifies a Diffie-Hellman private key with its associated parameters.

> > > Methods in `DHPrivateKeySpec`
> > > | Method | Description
> > > `BigInteger getG()` | Returns the base generator `g`.
> > > `BigInteger getP()` | Returns the prime modulus `p`.
> > > `BigInteger getX()` | Returns the private value `x`.

> > ### The `DHPublicKeySpec` Class

> > > This class (which implements the `KeySpec` interface) specifies a Diffie-Hellman public key with its associated parameters.

> > > Methods in `DHPublicKeySpec`
> > > | Method | Description
> > > `BigInteger getG()` | Returns the base generator `g`.
> > > `BigInteger getP()` | Returns the prime modulus `p`.
> > > `BigInteger getY()` | Returns the public value `y`.

> > ### The `DESKeySpec` Class

> > > This class (which implements the `KeySpec` interface) specifies a DES key.

> > > Methods in `DESKeySpec`
> > > | Method | Description
> > > `byte[] getKey()` | Returns the DES key bytes.
> > > `static boolean isParityAdjusted(byte[] key, int offset)` | Checks if the given DES key material is parity-adjusted.
> > > `static boolean isWeak(byte[] key, int offset)` | Checks if the given DES key material is weak or semi-weak.

> > ### The `DESedeKeySpec` Class

> > > This class (which implements the `KeySpec` interface) specifies a DES-EDE (Triple DES) key.

> > > Methods in `DESedeKeySpec`
> > > | Method | Description
> > > `byte[] getKey()` | Returns the DES-EDE key.
> > > `static boolean isParityAdjusted(byte[] key, int offset)` | Checks if the given DES-EDE key is parity-adjusted.

> > ### The `PBEKeySpec` Class

> > > This class implements the `KeySpec` interface. A user-chosen password can be used with password-based encryption (PBE); the password can be viewed as a type of raw key material. An encryption mechanism that uses this class can derive a cryptographic key from the raw key material.

> > > Methods in `PBEKeySpec`
> > > | Method | Description
> > > `void clearPassword` | Clears the internal copy of the password.
> > > `int getIterationCount` | Returns the iteration count or 0 if not specified.
> > > `int getKeyLength` | Returns the to-be-derived key length or 0 if not specified.
> > > `char[] getPassword` | Returns a copy of the password.
> > > `byte[] getSalt` | Returns a copy of the salt or null if not specified.

> > ### The `SecretKeySpec` Class

> > > This class implements the `KeySpec` interface. Since it also implements the `SecretKey` interface, it can be used to construct a `SecretKey` object in a provider-independent fashion, i.e., without having to go through a provider-based `SecretKeyFactory`.

> > > Methods in `SecretKeySpec`
> > > | Method | Description
> > > `boolean equals (Object obj)` | Indicates whether some other object is "equal to" this one.
> > > `String getAlgorithm()` | Returns the name of the algorithm associated with this secret key.
> > > `byte[] getEncoded()` | Returns the key material of this secret key.
> > > `String getFormat()` | Returns the name of the encoding format for this secret key.
> > > `int hashCode()` | Calculates a hash code value for the object.

> ## Secret-Key Generation

> > If you provide a secret-key generator (subclass of `javax.crypto.KeyGeneratorSpi`) for a particular secret-key algorithm, you may return the generated secret-key object (which must be an instance of `javax.crypto.SecretKey`, see `engineGenerateKey`) in one of the following ways:
> > - You implement a class whose instances represent secret-keys of the algorithm associated with your key generator. Your key generator implementation returns instances of that class. This approach is useful if the keys generated by your key generator have provider-specific properties.

> > - Your key generator returns an instance of `SecretKeySpec`, which already implements the `javax.crypto.SecretKey` interface. You pass the (raw) key bytes and the name of the secret-key algorithm associated with your key generator to the `SecretKeySpec` constructor. This approach is useful if the underlying (raw) key bytes can be represented as a byte array and have no key-parameters associated with them.

> ## Ensuring Exportability

> > A key feature of JCE is the exportability of the JCE framework and of the provider cryptography implementations if certain conditions are met.

> > Due to import control restrictions by the governments of a few countries, the jurisdiction policy files shipped with the Java 2 SDK, v 1.4 from Sun Microsystems specify that "strong" but limited cryptography may be used. An "unlimited" version of these files indicating no restrictions on cryptographic strengths is available for those living in eligible countries (which is most countries). But only the "strong" version can be imported into those countries whose governments mandate restrictions. The JCE framework will enforce the restrictions specified in the installed jurisdiction policy files.

> > As noted elsewhere, you can write just one version of your provider software, implementing cryptography of maximum strength. It is up to JCE, not your provider, to enforce any jurisdiction policy file-mandated restrictions regarding the cryptographic algorithms and maximum cryptographic strengths available to applets/applications in different locations.

> > The conditions that must be met by your provider in order to enable it to be plugged into JCE in the Java 2 SDK, v 1.4 are the following:

> > - The constructor of each SPI implementation class should do self-integrity checking, as described in How a Provider Can Do Self-Integrity Checking.

> > - The provider code should be written in such a way that provider classes become unusable if instantiated by an application directly, bypassing JCE. See Step 1: Write Your Service Implementation Code in the Steps to Implement and Integrate a Provider section.

> > - The provider package must be signed by an entity trusted by the JCE framework. (See Step 5a through Step 5c.) U.S. vendors whose providers may be exported outside the U.S. first need to apply for U.S. government export approval. (See Step 8.)

# Appendix A: The "SunJCE" Provider's Master Class

> Below is an edited version of the `SunJCE.java` file, which contains a class named `SunJCE` that is the master class for the provider named "SunJCE".

> 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 "SunJCE" provider. This information is used by the `getInstance` methods of the engine classes to look up the various algorithms and other services when they are requested.

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