Security information

The following pages contain documentation, example code, and ancillary files relating to IBM's SDKs. The documentation covers IBM-specific features of IBM's offerings. A platform-specific Security User Guide is included in each download. For information about the SDK for z/OS product and security components specific to that platform, see this Web site.

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Copyright Information

Note: Before using this information and the product it supports, be sure to read the general information under Notices.

(c) Copyright Sun Microsystems, Inc. 1998, 2005, 901 San Antonio Rd., Palo Ato, CA 94303 USA. All rights reserved.

(c) Copyright International Business Machines Corporation, 1998, 2005. All rights reserved.

U.S. Government Users Restricted Rights - Use, duplication or disclosure restricted by GSA ADP Schedule Contract with IBM Corp.

Introduction

Features and Benefits

JSSE Standard API

IBMJSSE2 Provider

What's New

Known Differences Between the Original IBMJSSE and the IBMJSSE2 Provider

Known Differences Between the IBM JSSE and the Sun JSSE Provider

Related Documentation

Terms and Definitions

Secure Sockets Layer (SSL) Protocol Overview

Why Use SSL?

How SSL Works

Key Classes

Relationship Between Classes

Core Classes and Interfaces

SocketFactory and ServerSocketFactory Classes

SSLSocketFactory and SSLServerSocketFactory Classes

SSLSocket and SSLServerSocket Classes

Non-blocking I/O with SSLEngine

SSLSession Interface

HttpsURLConnection Class

Support Classes and Interfaces

SSLContext Class

TrustManager Interface

TrustManagerFactory Class

X509TrustManager Interface

KeyManager Interface

KeyManagerFactory Class

X509KeyManager Interface

Relationships between TrustManagers and KeyManagers

Secondary Support Classes and Interfaces

SSLSessionContext Interface

SSLSessionBindingListener Interface

SSLSessionBindingEvent Class

HandShakeCompletedListener Interface

HandShakeCompletedEvent Class

HostnameVerifier Interface

X509Certificate Class

Previous (JSSE 1.0.x) Implementation Classes and Interfaces

Customizing JSSE

The Installation Directory <java-home>

Customization

JCE and Hardware Acceleration/Smartcard Support

Use of JCE

Hardware Accelerators

Configure JSSE to use Smartcards as Keystore and Trust Stores

Multiple and Dynamic Keystores

Kerberos Cipher Suites

Kerberos Requirements

Peer Identity Information

Security Manager

Additional Keystore Formats (PKCS12)

Running the IBMJSSE2 in FIPS Mode

Enabling FIPS Mode

Troubleshooting

Configuration Problems

Debugging Utilities

Code Examples

SSL Server using Hardware Cryptography through a IBMPKCS11Impl provider

SSL Server using Hardware Accelerator through a IBMPKCS11Impl provider

Appendix A: Standard Names

Appendix B: Provider Pluggability

Introduction

Data that travels across a network can easily be accessed by someone who is not the intended recipient. When the data includes private information, such as passwords and credit card numbers, steps must be taken to make the data unintelligible to unauthorized parties. It is also important to ensure the data has not been modified, either intentionally or unintentionally, during transport. The Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols were designed to help protect the privacy and integrity of data while it is transferred across a network.

The Java Secure Socket Extension (JSSE) enables secure Internet communications. It provides a framework and an implementation for a Java version of the SSL and TLS protocols and includes functionality for data encryption, server authentication, message integrity, and optional client authentication. Using JSSE, developers can provide for the secure passage of data between a client and a server running any application protocol, such as Hypertext Transfer Protocol (HTTP), Telnet, or FTP, over TCP/IP. (For an introduction to SSL, see Secure Sockets Layer (SSL) Protocol Overview.)

By abstracting the complex underlying security algorithms and "handshaking" mechanisms, JSSE minimizes the risk of creating subtle, but dangerous security vulnerabilities. Furthermore, it simplifies application development by serving as a building block that developers can integrate directly into their applications.

JSSE was previously an optional package (standard extension) to the Java 2 SDK, Standard Edition (SDK) versions 1.2 and 1.3. JSSE has now been integrated into the SDK, v 1.4.

JSSE provides both an application programming interface (API) framework and an implementation of that API. The JSSE API supplements the "core" network and cryptographic services defined in the Java 2 SDK, v1.4 and later java.security and java.net packages by providing extended networking socket classes, trust managers, key managers, SSLContexts, and a socket factory framework for encapsulating socket creation behavior. It also provides a limited public key certificate API that is compatible with Java Development Kit (JDK) 1.1-based platforms. However, please note that this limited javax.security.cert certificate API is provided only for backward compatibility with JSSE 1.0.x and should not be used. Instead, use the standard java.security.cert certificate API. Because the socket APIs were based on a blocking I/O model, in SDK 5, a non-blocking SSLEngineAPI was introduced to allow implementations to choose their own I/O methods.

The JSSE API is capable of supporting SSL versions 2.0 and 3.0 and Transport Layer Security (TLS) 1.0. These security protocols encapsulate a normal bidirectional stream socket and the JSSE API adds transparent support for authentication, encryption, and integrity protection. The IBMJSSE2 implementation in the SDK 1.4 and later implements SSL 3.0 and TLS 1.0. It does not implement SSL 2.0.

As mentioned above, JSSE is a security component of the Java 2 platform, and is based on the same design principles found elsewhere in the Java Cryptography Architecture (JCA) framework. This framework for cryptography-related security components allows them to have implementation independence and, whenever possible, algorithm independence. JSSE uses the same "provider" architecture defined in the JCA.

Other security components in the Java 2 platform include the Java Cryptography Extension (JCE), the Java Authentication and Authorization Service (JAAS), and the Java Security Tools. JSSE encompasses many of the same concepts and algorithms as those in JCE but automatically applies them underneath a simple stream socket API.

The JSSE APIs were designed to allow other SSL/TLS protocol and Public Key Infrastructure (PKI) implementations to be plugged in seamlessly. Developers can also provide alternate logic for determining if remote hosts should be trusted or what authentication key material should be sent to a remote host.

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Note: With the latest U.S. government export regulations, JSSE in SDK 5 allows any JSSE provider be used--as long as it supports the cipher suites shown in the Provider Pluggability list in the Appendix. The TrustManagerFactory and KeyManagerFactory are still fully pluggable.

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Features and Benefits

JSSE includes the following important features:

• Implemented in 100% Pure Java

• Can be exported to most countries

• Provides API support for SSL versions 2.0 and 3.0, and an implementation of SSL version 3.0
• Provides API support and an implementation for TLS version 1.0

• Includes classes that can be instantiated to create secure channels (SSLSocket, SSLServerSocket, and SSLEngine)

• Provides support for cipher suite negotiation, which is part of the SSL handshaking used to initiate or verify secure communications

• Provides support for client and server authentication, which is part of the normal SSL handshaking

• Provides support for Hypertext Transfer Protocol (HTTP) encapsulated in the SSL protocol (HTTPS), which allows access to data such as web pages using HTTPS

• Provides server session management APIs to manage memory-resident SSL sessions

Cryptographic Functionality Available With JSSE

Cryptographic Algorithm *	Cryptographic Process	Key Lengths (Bits)
RSA	Authentication and key exchange	Dependent upon JCE Provider (authentication) Dependent upon JCE Provider (key exchange) 512 (key exchange)
RC4	Bulk encryption	128 128 (40 effective)
RC2	Bulk encryption	128
DES	Bulk encryption	64 (56 effective) 64 (40 effective)
Triple DES	Bulk encryption	192 (112 effective)
AES	Bulk encryption	256 128
Diffie-Hellman	Key agreement	1024   512
DSA	Authentication	1024

* Note: The IBMJSSE2 implementation uses the Java^TM Cryptography Extension (JCE) for all of its cryptographic algorithms.

JSSE Standard API

The JSSE standard API, available in the javax.net, javax.net.ssl and javax.security.cert packages, covers:

• Secure (SSL) sockets and server sockets.
• A non-blocking engine for producing and consuming streams of SSL/TLS data (SSLEngine).

• Factories for creating sockets, server sockets, SSL sockets, and SSL server sockets. Using socket factories you can encapsulate socket creation and configuration behavior.

• A class representing a secure socket context that acts as a factory for secure socket factories and engines.

• Key and trust manager interfaces (including X.509-specific key and trust managers), and factories that can be used for creating them.

• A class for secure HTTP URL connections (HTTPS).

• A public key certificate API compatible with JDK 1.1-based platforms.

IBMJSSE2 Provider

The JDK comes with a JSSE provider named "IBMJSSE2", which comes pre-installed and pre-registered with the JCA. This provider supplies the following cryptographic services:

• An implementation of the SSL 3.0 and TLS 1.0 security protocols.
• An implementation of the most common SSL and TLS cipher suites which encompass a combination of authentication, key agreement, encryption and integrity protection.
• An implementation of an X.509-based key manager which chooses appropriate authentication keys from a standard JCA KeyStore.
• An implementation of an X.509-based trust manager which implements rules for certificate chain path validation.
• Support for the PKCS12 and IBMPKCS11KS keystore type.

A table of the cipher suites that IBMJSSE2 supports and all of the reserved names can be found in Appendix A.

What's New

What's New in JSSE in SDK 5

The following change was introduced in the JSSE in version 1.5.0 SR5 of the Java 2 platform.

• When IBMJSSE2 is used as a server, if the SSLv3 protocol is to be used for the handshake, it will no longer agree to use any of the AES cipher suites. Previously, the selection of the cipher suite was independent of the protocol selected so one could do an old-style SSLv3 handshake but a more modern AES cipher suite. The TLS protocol is not affected by this change. This change was required in order to support Microsoft Vista clients.

The following enhancements were made in the JSSE in the Java 2 Platform Standard Edition 5:

• The IBMJSSE2 implementation uses the Java Cryptography Extension (JCE) for all its cryptographic algorithms. See Customizing the Encryption Algorithm Providers for more information.
• SSLEngine (Non-blocking I/O) allows SSL/TLS applications to choose their own I/O and compute models.
• Kerberos cipher suites are available if the underlying OS supports it.
• Enhanced JCE and hardware accelerator/Smartcard support for performance enhancements and securely storing private data.
• Enhanced TrustManager support
• Provider pluggability
• HTTP/HTTPS enhancements
• Original JSSE has been removed
• Default Protocol Change
• Anonymous Cipher Suites Not Enabled by Default

Original JSSE has been removed

In 1.4.2, there were two JSSE providers supplied. In 5.0, the original IBMJSSE provider has been removed and replaced solely with the IBMJSSE2 provider. The IBMJSSE2 provider is now the preregistered JSSE provider in the java.security security properties file that is included in the SDK, V5.0. The deprecated com.ibm.net.ssl classes have been removed along with the com.ibm.net.ssl.internal.www.protocol.handler and com.ibm.net.ssl.www.protocol.handler. See Known Differences between the IBM Original JSSE Provider and the IBMJSSE2 Provider for migration assistance.

Default Protocol Changed

If an internal default context is used, (e.g. a SSLContext is created by SSLSocketFactory.getDefault() or SSLServerSocketFactory.getDefault()), an SSLContext with protocol of "SSL_TLS" will be implemented. Previously, the default was "SSL".

Anonymous Cipher Suites Not Enabled by Default

In previous SDKs, anonymous and null cipher suites were enabled by default. As these cipher suites are not recommended to be used due the minimal security they provide, they are now not enabled by default. See Accepting Anonymous Cipher Suites for information about using anonymous cipher suites.

Enhanced JCE and hardware accelerator/Smartcard support

The IBMJSSE2 Provider supported hardware cryptography in SDK 1.4.2. In order to be compatible with Sun's PKCS#11 support, a configuration file will now be required, even for code which ran successfully on SDK 1.4.2. This configuration file is specific to each hardware device and JSSE. See Enhanced JCE and hardware accelerator/Smartcard support for information about using hardware cryptography in SDK 5.0.

HTTP/HTTPS Enhancements

In SDK 5, a number of networking enhancements were made that affected HTTPS. Here is a summary of them.

• Connect and read timeouts. In SDK 1.4.x, the connect and read timeouts for protocol handlers could be set only by using some implementation-specific properties. In SDK 5, methods were added to URLConnection to allow timeouts to be set.
• Dynamic proxy server configuration and selection. Prior to SDK 5, proxy server configuration was static, global and configured via system properties. SDK 5 introduced new classes to allow proxies to be configured dynamically and on a per-URI basis.
• Pluggable cookie support. Prior to SDK 5, applications managed cookies by reading and setting HTTP headers. 1.5.0 introduced a new class to enable applications to install their own cookie handler that can retrieve cookies from a cookie cache for an HTTP request, and can save cookies from an HTTP response into a cookie cache.
• Pluggable caching support. Some classes were introduced in SDK 5 to allow applications to install a handler that can cache URL responses.

For details about these enhancements, see the SDK 5 Release Notes.

New/Updated Methods and Classes in SDK 5

SSLEngine and SSLEngineResult were added to support non-blocking I/O. SSLContext and SSLContextSpi were updated to generate SSLEngines.

A set of new methods were introduced to HandshakeCompletedEvent, HttpsURLConnection, and SSLSession which allow retrieval of Principals used by a session. (For example: X500Principal for X509 based ciphersuites, KerberosPrincipal for Kerberos suites, etc.) If an attempt is made to obtain the certificate chain for a session which does use certificates (Kerberos cipher suites), a SSLPeerUnverifiedException will occur.

New constructors were added to SSLException to support exception chaining.

A new method was added to SSLSession to determine whether a session is valid and available for resuming/joining. Another method was added to determine the port infomation of the session, if available. Lastly, two methods were added to determine the largest buffer sizes necessary when using SSLEngine.

A new abstract class X509ExtendedKeyManager was added to provide for SSLEngine extensions of the X509KeyManager interface. SSLContexts require initialization with an X509ExtendedKeyManager before using SSLEngines.

Two ManagerFactoryParameters factory classes were added. CertPathTrustManagerParameters allows passing of validation settings to CertPath-based TrustManagers. KeyStoreBuilderParameters was added to support dynamic key stores. (See the KeyStore.Builder class or the Multiple and Dynamic Keystores section for more information on dynamic KeyStores.)

The rest of this section highlights the differences between the JSSE in releases 1.4.2 and 1.4 of the Java 2 Platform and earlier releases.

What's New in JSSE in the SDK 1.4.2

New IBMJSSE2 Provider

The IBMJSSE2 provider is a new provider included in the SDK, v1.4.2. It is not preregistered in the java.security security properties file that is included with the SDK, v1.4.2. This section describes the enhancements that have been added to the new IBMJSSE2 Provider.

Note: The IBMJSSE2 provider in SDK 5, is now the preregistered JSSE provider.

• Includes improved serviceability
• Uses IBM cryptographic providers
• No longer needs to be FIPS certified
• Supports using JSSE with hardware cryptographic accelerators and hardware keys
• Supports a second, PKIK-compliant TrustManager

Serviceability

The tracing and debugging information supplied has been improved in order to assist with problem determination. The IBM debug JAR file is no longer required when tracing is required. The tracing is now configurable; see Debugging Utilities for more information.

Cryptographic providers

The Java Cryptography Extension (JCE) is a set of packages that provides a framework and implementations for encryption, key generation and key agreement, and message authentication code (MAC) algorithms. The original IBMJSSE Provider used it own internal cryptographic code. The IBMJSSE2 Provider uses the IBM JCE providers, IBMJCE, IBMJCE4758 and IBMPKCS11Impl, exclusively. The IBMJSSE2 provider cannot be configured to use another JCE provider due to U.S. government export regulations.

Note: Due to provider pluggability, IBMJSSE2 in SDK 5, will now use any JCE provider.

FIPS certification

Because the IBMJSSE2 provider no longer contains cryptographic code, it is not required to be FIPS certified. It leverages its cryptographic support from the IBMJCEFIPS provider. Support and updates can be applied to JSSE without requiring FIPS recertification, as long as the IBMJCEFIPS is certified. IBM JVM build 1.4.2sr1a or later is required. See "Running IBMJSSE2 in FIPS mode" for more information on setting up JSSE2 to run in FIPS mode.

Use of JSSE with hardware cryptographic accelerators and hardware keys

The IBMJSSE2 provider can be configured to use hardware cryptographic accelerators for potential performance improvements and to use hardware cryptographic cards as keystores for greater flexibility in key and trust management. The IBMJSSE2 provider uses the IBMJCE4758 provider on z/OS to provide hardware cryptographic support and IBMPKCS11Impl on all other platforms. See the IBM Java PKCS11 Implementation Provider for further information on setting up the IBMPKCS11Impl provider and hardware cryptographic cards that it supports.

Support in the IBM JCE hardware cryptographic providers also enable access to hardware keystores. To use a hardware keystore or truststore, set the keystore provider to PKCS11IMPLKS, for a PKCS#11 type keystore. Configure the hardware JCE provider and add the hardware JCE provider to the provider list. The hardware JCE provider will now be used for all JSSE cryptographic functions including the handling of the cryptographic hardware keys in the keystore.

Note 1: Due to provider pluggability in SDK 5, IBMJSSE2 will now use any JCE provider including JCE hardware providers. IBMJSSE2 is now dependent upon the hardware configuration file which is specific for each hardware cryptographic card. IBMJSSE2 will not be able to support hardware properly without the proper configuration file. Applications which ran in SDK 1.4.2, will need to be modified in include the proper configuration file for SDK 5.0.

Note 2: In order to use hardware crypto, the hardware JCE provider must be before the software JCE provider.

See the IBM Java PKCS11 Implementation Provider and the sample configuration files for further information.

Use of a second PKIX Compliant TrustManager

In addition to the simple X.509-based trustmanager previously available in the IBMJSSE provider, the IBMJSSE2 provider now supports a second, PKIX-compliant trust manager. It is implemented using the default CertPath PKIX implementation. For more information, see TrustManagerFactory Class.

Known Differences between the Original IBMJSSE Provider and the New IBMJSSE2 Provider

The known differences between the original JSSE provider and the new IBMJSSE2 provider are as follows. Code written to the original IBM JSSE provider might not compile or execute exactly as it did before.

• IBMJSSE2 Provider is called com.ibm.jsse2.IBMJSSEProvider2. In 5.0, it is pre-registered in the provider list.
• IBMJSSE2 provider HTTPS protocol handler is called com.ibm.net.ssl.www2.protocol.Handler.
• IBMJSSE2 provider does not support the com.ibm.net.ssl framework. Use the javax.net.ssl framework instead.
• IBMJSSE2 provider does not support the SSL version 2 protocol. The server side of a JSSE2 connection does accept SSLv2Hello.
• The AES_256 ciphers require the installation of the JCE Unlimited Strength Jurisdiction Policy. The original JSSE did not use JCE for its cryptographic support and therefore did not require these files.
• IBMJSSE2 provider requires a JCE provider.
• IBMJSSE2 does not build the server's private key certificate chain from the trusted keystore. The trusted certificates must be added to the server's private key to complete the chain. This is an incompatible change.
• IBMJSSE2 provider considers a certificate trusted if you have the private key.
• The IBMJSSE2 HTTPS performs hostname verification and rejects requests where a mismatch occurs between the host that you will connect to and the server name from the certificate. A HostnameVerification implementation called com.ibm.jsse2.HostnameVerifierIgnore is provided to always accept the connection even when a mismatch occurs.
• Tracing no longer requires the debug version of the IBMJSSE2 provider.
• The IBMJSSE2 implementation supports the new TrustManager which implements rules for the certificate chain path validation that Sun added to 1.4.2.
• The class com.ibm.jsse.KeyManagerFactoryParametersSpec(KeyStore ks, char[] password, String jceprovider) which was implemented for the IBMJCE4758 keystore has been removed. Convert code to use the IBMJCE4758KS directly through the keystore API and the IBMJCE4758 provider. (Applies to z/OS only.)
• The class com.ibm.jsse.SSLContext that is used to access secure token has been removed. Convert code that accesses token types of PKCS#12 to use the keystore API directory with a PKCS12 keystore type. Convert code that accesses token types of PKCS#11 to use the IBMPKCS11Impl JCE provider and IBMPKCS11ImplKS directly through the keystore API. Code that must use the PKCS#7 and MSCAPI token cannot use the new JSSE provider.
• IBMJSSE2 running in FIPS mode does not require a separate jar.
• IBMJSSE2 performs asynchronous key renegotiation. IBMJSSE performed synchronous key renegotation.

Known Differences between the IBMJSSE2 Provider and the Sun JSSE Provider

The known differences between the IBM JSSE and the Sun JSSE implementation are as follows. They do not affect API specifications or JSSE architecture. See the appropriate sections of the document for details.

• IBM JSSE provider is called com.ibm.jsse2.IBMJSSEProvider2.
• IBM KeyManagerFactory is called IbmX509.
• IBM TrustManagerFactory is called IbmX509 or IbmPKIX.
• IBM HTTPS protocol handler is called com.ibm.net.ssl.www2.protocol.Handler.
• The IBMJSSE2 provider does not support the com.sun.net.ssl framework. Use the javax.net.ssl framework instead.
• PKIK revocation checking can be used by setting the system property com.ibm.jsse2.checkRevocation to true.
• IBM implementation supports the following protocols: SSL, SSLv3, TLS, TLSv1, and SSL_TLS for engine class SSLContext or the API setEnabledProtocols in the SSLSocket or SSLServerSocket classes. It does not support specifying SSLv2Hello. A server side connection always accepts an SSLv2Hello. The IBM SSLContext getInstance factory method can be used to control which protocols actually get enabled for an SSL connection. Using the SSLContext getInstance or the setEnabledProtocols method give the same result. The Sun JSSE controls which protocols are actually enabled for an SSL connection through setEnabledProtocols.
• IBM and Sun support different ciphers. See Supported Cipher Suites for list of ciphers the IBM JSSE supports.
• The IBM JSSE TrustManager does not allow anonymous ciphers. In order to handshake on an anonymous cipher, a custom TrustManager that allows anonymous ciphers must be provided. See Accepting Anonymous Cipher Suites for information about creating your own X509TrustManager.
• When a null KeyManager is passed to SSLContext, the IBM JSSE KeyManagerFactory implemention will check system properties, then jssecacerts, if it exists, and finally use cacerts file to find the key material. The Sun JSSE will create an empty KeyManager. See KeyManager Class for further information.
• The IBM JSSE X509TrustManager and X509KeyManager will throw an exception if the TrustStore or KeyStore that is specified by system properties does not exist, of if the password is incorrect or the keystore type is inappropriate for the actual keystore. The Sun X509TrustManager will create a default TrustManager or KeyManager with an empty keystore.
• The IBM JSSE implementation will verify the entire server or client certificate chain, including trusted certificates. For example, if a trusted certificate has expired, the handshake will fail, even though the expired certificate is trusted. The Sun JSSE will verify the certificate chain up to the trusted certificate. Verification will stop when it reaches a trusted certificate and the trusted certificate and beyond will not be verified.
• For the Sun implementation: DSA server certificates can use only *_DH*_* cipher suites. For the IBM implementation, if the Server has a DSA certificate only and only RSA* ciphers are enabled, the connection succeeds with an RSA cipher. DSA will be used for authentication and ephemeral RSA will be used for the key exchange.
• Sun does not provide a JSSE that supports FIPS.

Related Documentation

Java Secure Socket Extension Documentation

• JSSE API documentation:
  
  • javax.net package
  • javax.net.ssl package
  • javax.security.cert package

Java 2 Platform Security Documentation

• Java 2 security homepage:
  http://java.sun.com/security/
• The Java^TM Certification Path API Programmer's Guide:
  API_users_guide.html
• Tutorial for Java 2 platform security:
  http://java.sun.com/docs/books/tutorial/security1.2/
• Book on Java 2 platform security:
  Inside Java 2 Platform Security: Architecture, API Design, and Implementation by Li Gong. Addison Wesley Longman, Inc., 1999. ISBN: 0201310007. http://java.sun.com/docs/books/security/index.html

Export Issues Related to Cryptography

For information on U.S. encryption policies, refer to these Web sites:

• U.S. Department of Commerce:
  http://www.commerce.gov
• Computer Systems Public Policy:
  http://www.techceocouncil.org/
• Federal Information Processing Standards Publications (FIPS PUBS) homepage, which has links to the Data Encryption Standard (DES):
  http://www.itl.nist.gov/fipspubs/
• Revised U.S. Encryption Export Control Regulations:
  http://www.epic.org/crypto/export_controls/regs_1_00.html

Cryptography Documentation

Online resources:

• Dr. Rivest's Cryptography and Security page:
  http://theory.lcs.mit.edu/~rivest/crypto-security.html

Books:

• Applied Cryptography, Second Edition by Bruce Schneier. John Wiley and Sons, Inc., 1996.
• Cryptography Theory and Practice by Doug Stinson. CRC Press, Inc., 1995.
• Cryptography & Network Security: Principles & Practice by William Stallings. Prentice Hall, 1998.

Secure Sockets Layer Documentation

Online resources:

• The SSL Protocol version 3.0 Internet Draft:
  http://wp.netscape.com/eng/ssl3/ssl-toc.html
• The TLS Protocol version 1.0 RFC:
  http://www.ietf.org/rfc/rfc2246.txt
• "HTTP Over TLS" Information RFC:
  http://www.ietf.org/rfc/rfc2818.txt

Books:

• SSL and TLS: Designing and Building Secure Systems by Eric Rescorla. Addison Wesley Professional, 2000.
• SSL and TLS Essentials: Securing the Web by Stephen Thomas. John Wiley and Sons, Inc., 2000.
• Java 2 Network Security, Second Edition, by Marco Pistoia, Duane F Reller, Deepak Gupta, Milind Nagnur, and Ashok K Ramani. Prentice Hall, 1999. Copyright 1999 International Business Machines.
• Enterprise Java Security: Building Secure J2EE Applications, by Marco Pistoia, Nataraj Nagaratnam, Larry Koved, and Anthony Nadalin. Addison Wesley, 2004.

Terms and Definitions

There are several terms relating to cryptography that are used within this document. This section defines some of these terms.

Authentication

Authentication is the process of confirming the identity of a party with whom one is communicating.

Cipher Suite

A cipher suite is a combination of cryptographic parameters that define the security algorithms and key sizes used for authentication, key agreement, encryption, and integrity protection.

Certificate

A certificate is a digitally signed statement vouching for the identity and public key of an entity (person, company, and so on). Certificates can either be self-signed or issued by a Certification Authority (CA). Certification Authorities are entities that are trusted to issue valid certificates for other entities. Well-known CAs include VeriSign, Entrust, and GTE CyberTrust. X509 is a common certificate in this format, and certificates in this format can be managed by the JDK keytool.

Cryptographic Hash Function

A cryptographic hash function is similar to a checksum. Data is processed with an algorithm that produces a relatively small string of bits called a hash. A cryptographic hash function has three primary characteristics: it is a one-way function, meaning that it is not possible to produce the original data from the hash; a small change in the original data produces a large change in the resulting hash; and it does not require a cryptographic key.

Cryptographic Service Provider

In the JCA, implementations for various cryptographic algorithms are provided by cryptographic service providers, or "providers " for short. Providers are essentially packages that implement one or more engine classes for specific algorithms. An engine class defines a cryptographic service in an abstract fashion without a concrete implementation.

Digital Signature

A digital signature is the digital equivalent of a handwritten signature. It is used to ensure that data transmitted over a network was sent by whoever claims to have sent it and that the data has not been modified in transit. For example, an RSA-based digital signature is calculated by first computing a cryptographic hash of the data and then encrypting the hash with the sender's private key.

Encryption and Decryption

Encryption is the process of using a complex algorithm to convert an original message, or cleartext, to an encoded message, called ciphertext, that is unintelligible unless it is decrypted. Decryption is the process of producing cleartext from ciphertext. The algorithms used to encrypt and decrypt data typically come in two categories: secret key (symmetric) cryptography and public key (asymmetric) cryptography.

Handshake Protocol

The negotiation phase during which the two socket peers agree to use a new or existing session. The handshake protocol is a series of messages exchanged over the record protocol. At the end of the handshake new connection-specific encryption and integrity protection keys are generated based on the key agreement secrets in the session.

Key Agreement

Key agreement is a method by which two parties cooperate to establish a common key. Each side generates some data which is exchanged. These two pieces of data are then combined to generate a key. Only those holding the proper private initialization data will be able to obtain the final key. Diffie-Hellman (DH) is the most common example of a key agreement algorithm.

Key Exchange

One side generates a symmetric key and encrypts it using the peer's public key (typcially RSA). The data is then transmitted to the peer, who then decrypts the key using its corresponding private key.

Key Managers and Trust Managers

Key managers and trust managers use keystores for their key material. A key manager manages a keystore and supplies public keys to others as needed, for example, for use in authenticating the user to others. A trust manager makes decisions about who to trust based on information in the truststore it manages.

Keystores and Truststores

A keystore is a database of key material. Key material is used for a variety of purposes, including authentication and data integrity. There are various types of keystores available, including "PKCS12" and the IBM "JKS."

Generally speaking, keystore information can be grouped into two different categories: key entries and trusted certificate entries. A key entry consists of an entity's identity and its private key, and can be used for a variety of cryptographic purposes. In contrast, a trusted certificate entry only contains a public key in addition to the entity's identity. Thus, a trusted certificate entry can not be used where a private key is required, such as in a javax.net.ssl.KeyManager. In the JDK implementation of "JKS", a keystore may contain both key entries and trusted certificate entries.

A truststore is a keystore which is used when making decisions about what to trust. If you receive some data from an entity that you already trust, and if you can verify that the entity is the one it claims to be, then you can assume that the data really came from that entity.

An entry should be added only to a truststore if the user makes a decision to trust that entity. By either generating a keypair or by importing a certificate, the user has given trust to that entry, and as a result any entry in the keystore is considered a trusted entry.

It may be useful to have two different keystore files: one containing just your key entries, and the other containing your trusted certificate entries, including Certification Authority (CA) certificates. The former contains private information, while the latter does not. Using two different files instead of a single keystore file provides for a cleaner separation of the logical distinction between your own certificates (and corresponding private keys) and others' certificates. You could provide more protection for your private keys if you store them in a keystore with restricted access, while providing the trusted certificates in a more publicly accessible keystore if needed.

Message Authentication Code

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

A MAC mechanism that is based on cryptographic hash functions is referred to as HMAC. HMAC can be used with any cryptographic hash function, such as Message Digest 5 (MD5) and Secure Hash Algorithm (SHA), in combination with a secret shared key. HMAC is specified in RFC 2104.

Public Key Cryptography

Public key cryptography uses an encryption algorithm in which two keys are produced. One key is made public while the other is kept private. The public key and the private key are cryptographic inverses; what one key encrypts only the other key can decrypt. Public key cryptography is also called asymmetric cryptography.

Record Protocol

The record protocol packages all data whether application-level or as part of the handshake process into discrete records of data much like a TCP stream socket converts an application byte stream into network packets. The individual records are then protected by the current encryption and integrity protection keys.

Secret Key Cryptography

Secret key cryptography uses an encryption algorithm in which the same key is used both to encrypt and decrypt the data. Secret key cryptography is also called symmetric cryptography.

Session

A session is a named collection of state information including authenticated peer identity, cipher suite, and key agreement secrets which are negotiated through a secure socket handshake and that can be shared among multiple secure socket instances.

Trust Managers

See Key Managers and Trust Managers.

Truststore

See Keystores and Truststores.

Secure Sockets Layer (SSL) Protocol Overview

Secure Sockets Layer (SSL) is the most widely used protocol for implementing cryptography on the Web. SSL uses a combination of cryptographic processes to provide secure communication over a network. This section provides an introduction to SSL and the cryptographic processes it uses.

SSL provides a secure enhancement to the standard TCP/IP sockets protocol used for Internet communications. As shown in the "TCP/IP Protocol Stack With SSL" figure below, the secure sockets layer is added between the transport layer and the application layer in the standard TCP/IP protocol stack. The application most commonly used with SSL is Hypertext Transfer Protocol (HTTP), the protocol for Internet Web pages. Other applications, such as Net News Transfer Protocol (NNTP), Telnet, Lightweight Directory Access Protocol (LDAP), Interactive Message Access Protocol (IMAP), and File Transfer Protocol (FTP), can be used with SSL as well.

Note: There is currently no standard for secure FTP.

TCP/IP Protocol Stack With SSL

TCP/IP Layer	Protocol
Application Layer	HTTP, NNTP, Telnet, FTP, etc.
Secure Sockets Layer	SSL
Transport Layer	TCP
Internet Layer	IP

SSL was developed by Netscape in 1994, and with input from the Internet community, has evolved to become a standard. It is now under the control of the international standards organization, the Internet Engineering Task Force (IETF). The IETF has renamed SSL to Transport Layer Security (TLS), and released the first specification, version 1.0, in January 1999. TLS 1.0 is a modest upgrade to the most recent version of SSL, version 3.0. The differences between SSL 3.0 and TLS 1.0 are minor.

Why Use SSL?

Transferring sensitive information over a network can be risky due to the following three issues:

• You cannot always be sure that the entity with whom you are communicating is really who you think it is.

• Network data can be intercepted, so it is possible that it can be read by an unauthorized third party, sometimes known as an attacker.

• If an attacker can intercept the data, the attacker may be able to modify the data before sending it on to the receiver.

SSL addresses each of these issues. It addresses the first issue by optionally allowing each of two communicating parties to ensure the identity of the other party in a process called authentication. After the parties are authenticated, SSL provides an encrypted connection between the two parties for secure message transmission. Encrypting the communication between the two parties provides privacy and therefore addresses the second issue. The encryption algorithms used with SSL include a secure hash function, which is similar to a checksum. This ensures that data is not modified in transit. The secure hash function addresses the third issue of data integrity.

Note, both authentication and encryption are optional, and depend on the the negotiated cipher suites between the two entities.

The most obvious example of when you would use SSL is in an e-commerce transaction. In an e-commerce transaction, it would be foolish to assume that you can guarantee the identity of the server with whom you are communicating. It would be easy enough for someone to create a phony Web site promising great services if only you enter your credit card number. SSL allows you, the client, to authenticate the identity of the server. It also allows the server to authenticate the identity of the client, although in Internet transactions, this is seldom done.

After the client and the server are comfortable with each other's identity, SSL provides privacy and data integrity through the encryption algorithms it uses. This integrity allows sensitive information, such as credit card numbers, to be transmitted securely over the Internet.

While SSL provides authentication, privacy, and data integrity, it does not provide non-repudiation services. Non-repudiation means that an entity that sends a message cannot later deny that they sent it. When the digital equivalent of a signature is associated with a message, the communication can later be proved. SSL alone does not provide non-repudiation.

How SSL Works

One of the reasons SSL is effective is that it uses several different cryptographic processes. SSL uses public key cryptography to provide authentication, and secret key cryptography and digital signatures to provide for privacy and data integrity. Before you can understand SSL, it is helpful to understand these cryptographic processes.

Cryptographic Processes

The primary purpose of cryptography is to make it difficult for an unauthorized third party to access and understand private communication between two parties. It is not always possible to restrict all unauthorized access to data, but private data can be made unintelligible to unauthorized parties through the process of encryption. Encryption uses complex algorithms to convert the original message, or cleartext, to an encoded message, called ciphertext. The algorithms used to encrypt and decrypt data that is transferred over a network typically come in two categories: secret key cryptography and public key cryptography. These forms of cryptography are explained in the following subsections.

Both secret key cryptography and public key cryptography depend on the use of an agreed-upon cryptographic key or pair of keys. A key is a string of bits that is used by the cryptographic algorithm or algorithms during the process of encrypting and decrypting the data. A cryptographic key is like a key for a lock: only with the right key can you open the lock.

Safely transmitting a key between two communicating parties is not a trivial matter. A public key certificate allows a party to safely transmit its public key, while ensuring the receiver of the authenticity of the public key. Public key certificates are described in a later section.

In the descriptions of the cryptographic processes that follow, we use the conventions used by the security community: we label the two communicating parties with the names Alice and Bob. We call the unauthorized third party, also known as the attacker, Charlie.

Secret Key Cryptography

With secret key cryptography, both communicating parties, Alice and Bob, use the same key to encrypt and decrypt the messages. Before any encrypted data can be sent over the network, both Alice and Bob must have the key and must agree on the cryptographic algorithm that they will use for encryption and decryption.

One of the major problems with secret key cryptography is the logistical issue of how to get the key from one party to the other without allowing access to an attacker. If Alice and Bob are securing their data with secret key cryptography, and if Charlie gains access to their key, Charlie can understand any secret messages he intercepts between Alice and Bob. Not only can Charlie decrypt Alice's and Bob's messages, but he can also pretend that he is Alice and send encrypted data to Bob. Bob will not know that the message came from Charlie, not Alice.

When the problem of secret key distribution is solved, secret key cryptography can be a valuable tool. The algorithms provide excellent security and encrypt data relatively quickly. The majority of the sensitive data sent in an SSL session is sent using secret key cryptography.

Secret key cryptography is also called symmetric cryptography because the same key is used to both encrypt and decrypt the data. Well-known secret key cryptographic algorithms include the Data Encryption Standard (DES), triple-strength DES (3DES), Rivest Cipher 2 (RC2), and Rivest Cipher 4 (RC4).

Public Key Cryptography

Public key cryptography solves the logistical problem of key distribution by using both a public key and a private key. The public key can be sent openly through the network while the private key is kept private by one of the communicating parties. The public and the private keys are cryptographic inverses of each other; what one key encrypts, the other key will decrypt.

Let's assume that Bob wants to send a secret message to Alice using public key cryptography. Alice has both a public key and a private key, so she keeps her private key in a safe place and sends her public key to Bob. Bob encrypts the secret message to Alice using Alice's public key. Alice can later decrypt the message with her private key.

If Alice encrypts a message using her private key and sends the encrypted message to Bob, Bob can be sure that the data he receives comes from Alice; if Bob can decrypt the data with Alice's public key, the message must have been encrypted by Alice with her private key, and only Alice has Alice's private key. The problem is that anybody else can read the message as well because Alice's public key is public. While this scenario does not allow for secure data communication, it does provide the basis for digital signatures. A digital signature is one of the components of a public key certificate, and is used in SSL to authenticate a client or a server. Public key certificates and digital signatures are described in later sections.

Public key cryptography is also called asymmetric cryptography because different keys are used to encrypt and decrypt the data. A well known public key cryptographic algorithm often used with SSL is the Rivest Shamir Adleman (RSA) algorithm. Another public key algorithm used with SSL that is designed specifically for secret key exchange is the Diffie-Hellman (DH) algorithm. Public key cryptography requires extensive computations, making it very slow. It is therefore typically used only for encrypting small pieces of data, such as secret keys, rather than for the bulk of encrypted data communications.

A Comparison Between Secret Key and Public Key Cryptography

Both secret key cryptography and public key cryptography have strengths and weaknesses. With secret key cryptography, data can be encrypted and decrypted quickly, but since both communicating parties must share the same secret key information, the logistics of exchanging the key can be a problem. With public key cryptography, key exchange is not a problem since the public key does not need to be kept secret, but the algorithms used to encrypt and decrypt data require extensive computations, and are therefore very slow.

Public Key Certificates

A public key certificate provides a safe way for an entity to pass on its public key to be used in asymmetric cryptography. The public key certificate avoids the following situation: if Charlie creates his own public key and private key, he can claim that he is Alice and send his public key to Bob. Bob will be able to communicate with Charlie, but Bob will think that he is sending his data to Alice.

A public key certificate can be thought of as the digital equivalent of a passport. It is issued by a trusted organization and provides identification for the bearer. A trusted organization that issues public key certificates is known as a certificate authority (CA). The CA can be likened to a notary public. To obtain a certificate from a CA, one must provide proof of identity. When the CA is confident that the applicant represents the organization it says it represents, the CA signs the certificate attesting to the validity of the information contained within the certificate.

A public key certificate contains several fields, including:

• Issuer - The issuer is the CA that issued the certificate. If a user trusts the CA that issues a certificate, and if the certificate is valid, the user can trust the certificate.

• Period of validity - A certificate has an expiration date, and this date is one piece of information that should be checked when verifying the validity of a certificate.

• Subject - The subject field includes information about the entity that the certificate represents.

• Subject's public key - The primary piece of information that the certificate provides is the subject's public key. All the other fields are provided to ensure the validity of this key.

• Signature - The certificate is digitally signed by the CA that issued the certificate. The signature is created using the CA's private key and ensures the validity of the certificate. Because only the certificate is signed, not the data sent in the SSL transaction, SSL does not provide for non-repudiation.

If Bob only accepts Alice's public key as valid when she sends it in a public key certificate, Bob will not be fooled into sending secret information to Charlie when Charlie masquerades as Alice.

Multiple certificates may be linked in a certificate chain. When a certificate chain is used, the first certificate is always that of the sender. The next is the certificate of the entity that issued the sender's certificate. If there are more certificates in the chain, each is that of the authority that issued the previous certificate. The final certificate in the chain is the certificate for a root CA. A root CA is a public certificate authority that is widely trusted. Information for several root CAs is typically stored in the client's Internet browser. This information includes the CA's public key. Well-known CAs include VeriSign, Entrust, and GTE CyberTrust.

Cryptographic Hash Functions

When sending encrypted data, SSL typically uses a cryptographic hash function to ensure data integrity. The hash function prevents Charlie from tampering with data that Alice sends to Bob.

A cryptographic hash function is similar to a checksum. The main difference is that while a checksum is designed to detect accidental alterations in data, a cryptographic hash function is designed to detect deliberate alterations. When data is processed by a cryptographic hash function, a small string of bits, known as a hash, is generated. The slightest change to the message typically makes a large change in the resulting hash. A cryptographic hash function does not require a cryptographic key. Two hash functions often used with SSL are Message Digest 5 (MD5) and Secure Hash Algorithm (SHA). SHA was proposed by the U.S. National Institute of Science and Technology (NIST).

Message Authentication Code

A message authentication code (MAC) is similar to a cryptographic hash, except that it is based on a secret key. When secret key information is included with the data that is processed by a cryptographic hash function, the resulting hash is known as an HMAC.

If Alice wants to be sure that Charlie does not tamper with her message to Bob, she can calculate an HMAC for her message and append the HMAC to her original message. She can then encrypt the message plus the HMAC using a secret key she shares with Bob. When Bob decrypts the message and calculates the HMAC, he will be able to tell if the message was modified in transit. With SSL, an HMAC is used with the transmission of secure data.

Digital Signatures

Once a cryptographic hash is created for a message, the hash is encrypted with the sender's private key. This encrypted hash is called a digital signature.

The SSL Process

Communication using SSL begins with an exchange of information between the client and the server. This exchange of information is called the SSL handshake.

The three main purposes of the SSL handshake are:

• Negotiate the cipher suite

• Authenticate identity (optional)

• Establish information security by agreeing on encryption mechanisms

Negotiating the Cipher Suite

The SSL session begins with a negotiation between the client and the server as to which cipher suite they will use. A cipher suite is a set of cryptographic algorithms and key sizes that a computer can use to encrypt data. The cipher suite includes information about the public key exchange algorithms, secret key encryption algorithms, and cryptographic hash functions. The client tells the server which cipher suites it has available, and the server chooses the best mutually acceptable cipher suite.

Authenticating the Server

In SSL, the authentication step is optional, but in the example of an e-commerce transaction over the Web, the client will generally want to authenticate the server. Authenticating the server allows the client to be sure that the server represents the entity that the client believes the server represents.

To prove that a server belongs to the organization that it claims to represent, the server presents its public key certificate to the client. If this certificate is valid, the client can be sure of the identity of the server.

The client and server exchange information that allows them to agree on the same secret key. For example, with RSA, the client uses the server's public key, obtained from the public key certificate, to encrypt the secret key information. The client sends the encrypted secret key information to the server. Only the server can decrypt this message since the server's private key is required for this decryption.

Sending the Encrypted Data

Both the client and the server now have access to the same secret key. With each message, they use the cryptographic hash function, chosen in the first step of this process, and shared secret information, to compute an HMAC that they append to the message. They then use the secret key and the secret key algorithm negotiated in the first step of this process to encrypt the secure data and the HMAC. The client and server can now communicate securely using their encrypted and hashed data.

The SSL Protocol

The previous section provides a high-level description of the SSL handshake, which is the exchange of information between the client and the server prior to sending the encrypted message. This section provides more detail.

The "SSL Messages" figure below shows the sequence of messages that are exchanged in the SSL handshake. Messages that are only sent in certain situations are noted as optional. Each of the SSL messages is described in the following figure:

The SSL messages are sent in the following order:

1. Client hello - The client sends the server information including the highest version of SSL it supports and a list of the cipher suites it supports. (TLS 1.0 is indicated as SSL 3.1.) The cipher suite information includes cryptographic algorithms and key sizes.
2. Server hello - The server chooses the highest version of SSL and the best cipher suite that both the client and server support and sends this information to the client.

3. Certificate - The server sends the client a certificate or a certificate chain. A certificate chain typically begins with the server's public key certificate and ends with the certificate authority's root certificate. This message is optional, but is used whenever server authentication is required.

4. Certificate request - If the server needs to authenticate the client, it sends the client a certificate request. In Internet applications, this message is rarely sent.

5. Server key exchange - The server sends the client a server key exchange message when the public key information sent in 3) above is not sufficient for key exchange.

6. Server hello done - The server tells the client that it is finished with its initial negotiation messages.

7. Certificate - If the server requests a certificate from the client in Message 4, the client sends its certificate chain, just as the server did in Message 3.

   Note: Only a few Internet server applications ask for a certificate from the client.

8. Client key exchange - The client generates information used to create a key to use for symmetric encryption. For RSA, the client then encrypts this key information with the server's public key and sends it to the server.

9. Certificate verify - This message is sent when a client presents a certificate as above. Its purpose is to allow the server to complete the process of authenticating the client. When this message is used, the client sends information that it digitally signs using a cryptographic hash function. When the server decrypts this information with the client's public key, the server is able to authenticate the client.

10. Change cipher spec - The client sends a message telling the server to change to encrypted mode.

11. Finished - The client tells the server that it is ready for secure data communication to begin.

12. Change cipher spec - The server sends a message telling the client to change to encrypted mode.

13. Finished - The server tells the client that it is ready for secure data communication to begin. This is the end of the SSL handshake.

14. Encrypted data - The client and the server communicate using the symmetric encryption algorithm and the cryptographic hash function negotiated in Messages 1 and 2, and using the secret key that the client sent to the server in Message 8.
15. Close Messages - At the end of the connection, each side will send a close_notify message to inform the peer that the connection is closed.

If the parameters generated during an SSL session are saved, these parameters can sometimes be re-used for future SSL sessions. Saving SSL session parameters allows encrypted communication to begin much more quickly.

Cipher Suite Choice and Remote Entity Verification

The SSL/TLS protocols define a specific series of steps to ensure a "protected" connection. However, the choice of cipher suite will directly impact the type of security the connection enjoys. For example, if an anonymous cipher suite is selected, the application will have no way to verify the remote peer's identity. If a suite with no encryption is selected, then the privacy of the data can not be protected. Additionally, the SSL/TLS protocols do not specify that the credentials received must match those that peer might be expected to send. If the connection were somehow redirected to a rogue peer, but the rogue's credentials presented were acceptable based on the current trust material, the connection would be considered valid.

When using raw SSLSockets/SSLEngines you should always check the peer's credentials before sending any data. The SSLSocket and SSLEngine classes do not automatically verify that the hostname in a URL matches the hostname in the peer's credentials. An application could be exploited with URL spoofing if the hostname is not verified.

Protocols such as https do require hostname verification. Applications can use HostnameVerifier to override the default HTTPS hostname rules. See HttpsURLConnection for more information.

SSL and TLS References

For a list of resources containing more information about SSL, see Secure Sockets Layer Documentation .

Key Classes

Relationship Between Classes

To communicate securely, both sides of the connection must be SSL-enabled. In the JSSE API, the endpoint classes of the connection is the SSLSocket and SSLEngine. In the diagram below, the major classes used to create SSLSocket/SSLEngines are laid out in a logical ordering.

An SSLSocket is created either by an SSLSocketFactory or by an SSLServerSocket accepting an in-bound connection. (In turn, an SSLServerSocket is created by an SSLServerSocketFactory.) Both SSLSocketFactory and SSLServerSocketFactory objects are created by an SSLContext. An SSLEngine is created directly by the SSLContext, and relies on the application to handle all I/O.

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IMPORTANT NOTE: When using raw SSLSockets/SSLEngines you should always check the peer's credentials before sending any data. The SSLSocket/SSLEngine classes do not automatically verify, for example, that the hostname in a URL matches the hostname in the peer's credentials. An application could be exploited with URL spoofing if the hostname is not verified.

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There are two ways to obtain and initialize an SSLContext:

• The simplest is to call the static getDefault method on either the SSLSocketFactory or SSLServerSocketFactory class. These methods create a default SSLContext with a default KeyManager, TrustManager, default SSL provider, and a secure random number generator. (A default KeyManagerFactory and TrustManagerFactory are used to create the KeyManager and TrustManager, respectively.) The key material used is found in the default keystore or truststore, as determined by system properties described in Customizing the Default Key and Trust Stores, Store Types, and Store Passwords.

• The approach that gives the caller the most control over the behavior of the created context is to call the static method getInstance on the SSLContext class, then initialize the context by calling the instance's proper init method. One variant of the init method takes three arguments: an array of KeyManager objects, an array of TrustManager objects, and a SecureRandom random number generator. The KeyManager and TrustManager objects are created by either implementing the appropriate interface(s) or using the KeyManagerFactory and TrustManagerFactory classes to generate implementations. The KeyManagerFactory and TrustManagerFactory can then each be initialized with key material contained in the KeyStore passed as an argument to the TrustManagerFactory and KeyManagerFactory init method. Finally, the getTrustManagers method (in TrustManagerFactory) and getKeyManagers method (in KeyManagerFactory) can be called to obtain the array of trust or key managers, one for each type of trust or key material.

Once an SSL connection is established, an SSLSession is created which contains various information, such as identities established, cipher suite used, and so on. The SSLSession is then used to describe an ongoing relationship and state information between two entities. Each SSL connection involves one session at a time, but that session may be used on many connections between those entities, simultaneously or sequentially.

Core Classes and Interfaces

The core JSSE classes are part of the javax.net and javax.net.ssl packages.

SocketFactory and ServerSocketFactory Classes

The abstract javax.net.SocketFactory class is used to create sockets. It must be subclassed by other factories, which create particular subclasses of sockets and thus provide a general framework for the addition of public socket-level functionality. (See, for example, SSLSocketFactory.)

The javax.net.ServerSocketFactory class is analogous to the SocketFactory class, but is used specifically for creating server sockets.

Socket factories are a simple way to capture a variety of policies related to the sockets being constructed, producing such sockets in a way which does not require special configuration of the code which asks for the sockets:

• Due to polymorphism of both factories and sockets, different kinds of sockets can be used by the same application code just by passing different kinds of factories.

• Factories can themselves be customized with parameters used in socket construction. So for example, factories could be customized to return sockets with different networking timeouts or security parameters already configured.

• The sockets returned to the application can be subclasses of java.net.Socket (or javax.net.ssl.SSLSocket), so that they can directly expose new APIs for features such as compression, security, record marking, statistics collection, or firewall tunneling.

SSLSocketFactory and SSLServerSocketFactory Classes

A javax.net.ssl.SSLSocketFactory acts as a factory for creating secure sockets. This class is an abstract subclass of javax.net.SocketFactory.

Secure socket factories encapsulate the details of creating and initially configuring secure sockets. This encapsulation includes authentication keys, peer certificate validation, enabled cipher suites and so on.

The javax.net.ssl.SSLServerSocketFactory class is analogous to the SSLSocketFactory class, but is used specifically for creating server sockets.

Obtaining an SSLSocketFactory

There are three primary ways of obtaining an SSLSocketFactory:

• Get the default factory by calling the SSLSocketFactory.getDefault static method.

• Receive a factory as an API parameter. That is, code that needs to create sockets but that doesn't care about the details of how the sockets are configured can include a method with an SSLSocketFactory parameter that can be called by clients to specify which SSLSocketFactory to use when creating sockets. (For example, javax.net.ssl.HttpsURLConnection.)

• Construct a new factory with specifically configured behavior.

The default factory is typically configured to support server authentication only so that sockets created by the default factory do not leak any more information about the client than a normal TCP socket would.

Many classes that create and use sockets do not need to know the details of socket creation behavior. Creating sockets through a socket factory that is passed in as a parameter is a good way of isolating the details of socket configuration, and increases the reusability of classes which create and use sockets.

You can create new socket factory instances either by implementing your own socket factory subclass or by using another class which acts as a factory for socket factories. One example of such a class is SSLContext, which is provided with the JSSE implementation as a provider-based configuration class.

SSLSocket and SSLServerSocket Classes

The javax.net.ssl.SSLSocket class is a subclass of the standard Java java.net.Socket class. It supports all of the standard socket methods and adds additional methods specific to secure sockets. Instances of this class encapsulate the SSLContext under which they were created. There are APIs to control the creation of secure socket sessions for a socket instance but trust and key management are not directly exposed.

The javax.net.ssl.SSLServerSocket class is analogous to the SSLSocket class, but is used specifically for creating server sockets.

To prevent peer spoofing, you should always verify the credentials presented to a SSLSocket.

Implementation note: Due to the complexity of the SSL and TLS protocols, it is difficult to predict whether incoming bytes on a connection are handshake or application data, and how that data might affect the current connection state (even causing the process to block). In the IBM JSSE implementation, the available() method on the object obtained by SSLSocket.getInputStream() returns a count of the number of application data bytes successfully decrypted from the SSL connection but not yet read by the application.

Obtaining an SSLSocket

Instances of SSLSocket can be obtained in two ways. First, an SSLSocket can be created by an instance of SSLSocketFactory via one of the several createSocket methods on that class. The second way to obtain SSLSockets is through the accept method on the SSLServerSocket class.

Non-blocking I/O with SSLEngine

SSL/TLS is becoming increasingly popular. It is being used in a wide variety of applications across a wide range of computing platforms and devices. Along with this popularity comes demands to use it with different I/O and threading models in order to satisfy the applications' performance, scalability, footprint, and other requirements. There are demands to use it with blocking and non-blocking I/O channels, asynchronous I/O, arbitrary input and output streams, and byte buffers. There are demands to use it in highly scalable, performance-critical environments, requiring management of thousands of network connections.

Prior to SDK 5, the JSSE API supported only a single transport abstraction: stream-based sockets via SSLSocket. While this was adequate for many applications, it did not meet the needs of applications that need to use different I/O or threading models. In 1.5.0, a new abstraction was introduced to allow applications to use the SSL/TLS protocols in a transport independent way, and thus freeing applications to choose transport and computing models that best meet their needs. Not only does this new abstraction allow applications to use non-blocking I/O channels and other I/O models, it also accommodates different threading models. This effectively leaves the I/O and threading decisions up to the application. Because of this flexibility, the application must now manage I/O and threading (complex topics in and of themselves), as well as have some understanding of the SSL/TLS protocols. The new abstraction is therefore an advanced API: beginners should continue to use SSLSocket.

Newcomers to the API may wonder "Why not just have an SSLSocketChannel which extends java.nio.channels.SocketChannel?" There are two main reasons:

• There were a lot of very difficult questions about what a SSLSocketChannel should be, including its class hierarchy and how it should interoperate with Selectors and other types of SocketChannels. Each proposal brought up more questions than answers. It was noted that any new API abstraction extended to work with SSL/TLS would require the same significant analysis and could result in large and complex APIs.

• Any JSSE implementation of a new API would be free to choose the "best" I/O & compute strategy, but hiding any of these details is inappropriate for those applications needing full control. Any specific implementation would be inappropriate for some application segment.

By abstracting the I/O and treating data as streams of bytes, these issues are resolved and the new API could be used with any existing or future I/O model. While this solution makes I/O and CPU handling the developers' responsibility, JSSE implementations are prevented from being unusable due to some unconfigurable and/or unchangeable internal detail.

Users of other Java programming language APIs such as JGSS and SASL will notice similarities in that the application is also responsible for transporting data.

SSLEngine

The core class in this new abstraction is javax.net.ssl.SSLEngine. It encapsulates an SSL/TLS state machine and operates on inbound and outbound byte buffers supplied by the user of the SSLEngine. The following diagram illustrates the flow of data from the application, to the SSLEngine, to the transport mechanism, and back.

The application, shown on the left, supplies application (plaintext) data in an application buffer and passes it to the SSLEngine. The