Security in Java 2 SDK 1.2 - Java Tutorial 5.0 英文版

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Trail: Security in Java 2 SDK 1.2

by Mary Dageforde

In this trail you'll learn how the built-in Java^TM security features protect you from malevolent programs. You'll see how to use tools to control access to resources, to generate and to check digital signatures, and to create and to manage keys needed for signature generation and checking. You'll also see how to incorporate cryptography services, such as digital signature generation and checking, into your programs.

The security features provided by the Java Development Kit (JDK^TM) 1.2 are intended for a variety of audiences:

Users running programs:

Built-in security functionality protects you from malevolent programs (including viruses), maintains the privacy of your files and information about you, and authenticates the identity of each code provider. For the first time, you can subject applications to security controls (just as is done for applets), when desired.
Developers:

You can use API methods to incorporate security functionality into your programs, including cryptography services and security checks. The API framework enables you to define and integrate your own permissions (controlling access to specific resources), cryptography service implementations, security manager implementations, and policy implementations. In addition, classes are provided for management of your public/private key pairs and public key certificates from people you trust.
Systems administrators, developers, and users:
JDK 1.2 tools manage your keystore (database of keys and certificates); generate digital signatures for JAR files, and verify the authenticity of such signatures and the integrity of the signed contents; and create and modify the policy files that define your installation's security policy.

Note: Nearly all of the security features documented in this trail were added to the JDK for its 1.2 release. Thus, the code examples in the following lessons will work only on Java platforms that are compatible with JDK 1.2. Individual browsers may have some different behavior, unless you use the Java Plug-in to download the latest Java Runtime Environment (JRE^TM) compatible with JDK 1.2.

Trail Lessons

Security Features Overview briefly describes the security features available in JDK 1.2.
Quick Tour of Controlling Applets provides an overview of some of the new features. This lesson shows how resource accesses, such as reading or writing a file, are not permitted for applets unless explicitly allowed by a permission in a policy file.
Quick Tour of Controlling Applications builds on the previous lesson, showing that when applications are run under a security manager, resource accesses may be controlled in exactly the same way as for applets.
API and Tools Use for Secure Code and File Exchanges describes digital signatures, certificates, and keystores and discusses why they are needed. It also provides overview information applicable to the next three lessons regarding the steps commonly needed for using the tools or the API to generate signatures, export/import certificates, and so on.
Signing Code and Granting It Permissions illustrates the use of all the security-related tools. It shows the steps that a developer would take to sign and to distribute code for others to run. The lesson also shows how someone who will run the code (or a system administrator) could add an entry in a policy file to grant the code permission for the resource accesses it needs.
Exchanging Files shows use of the tools by one person to sign an important document, such as a contract, and to export the public key certificate for the public key corresponding to the private key used to sign the contract. Then the lesson shows how another person, who receives the contract, the signature, and the public key certificate, can import the certificate and verify the signature.
Generating and Verifying Signatures walks you step by step through an example of writing a Java program using the JDK Security API to generate keys, to generate a digital signature for data using the private key, and to export the public key and the signature to files. Then the example shows writing a second program, which may be expected to run on a different person's computer, that imports the public key and verifies the authenticity of the signature. Finally, the example discusses potential weaknesses of the approach used by the basic programs and demonstrates possible alternative approaches and methods of supplying and importing keys, including in certificates.
Implementing Your Own Permission demonstrates how to write a class that defines its own special permission.
Summaries provides summaries of

general security and JDK security-specific terminology and concepts
the JDK Security API
the security-related tools
the security-related files

For More Information

JDK 1.2 security release documentation can be found at http://java.sun.com/products/jdk/1.2/docs/guide/security/index.html .Here you'll find more detailed information about the security features, including architecture specifications, usage guides, API documentation, and tool documentation.
This trail does not cover encryption and decryption. These are supplied as part of the Java Cryptography Extension (JCE). For more information, see the documentation for that release at http://java.sun.com/products/jce/index.html .
Information on use of the Java Plug-in to download the latest Java Runtime Environment compatible with JDK 1.2 can be found here: http://java.sun.com/products/plugin/index.html .

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