JRE 8 rt.jar is the JAR file for JRE 8 RT (Runtime) libraries. JRE (Java Runtime) 8 is the runtime environment included in JDK 8. JRE 8 rt.jar libraries are divided into 6 packages:

com.* - Internal Oracle and Sun Microsystems libraries
java.* - Standard Java API libraries.
javax.* - Extended Java API libraries.
jdk.* -  JDK supporting libraries.
org.* - Third party libraries.
sun.* - Old libraries developed by Sun Microsystems.

JAR File Information:

Directory of C:\fyicenter\jdk-1.8.0_191\jre\lib
      63,596,151 rt.jar

Here is the list of Java classes of the java.* package in JRE 1.8.0_191 rt.jar. Java source codes are also provided.

⏎ java/security/KeyPairGeneratorSpi.java

/*
 * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package java.security;

import java.security.spec.AlgorithmParameterSpec;

/**
 * <p> This class defines the <i>Service Provider Interface</i> (<b>SPI</b>)
 * for the {@code KeyPairGenerator} class, which is used to generate
 * pairs of public and private keys.
 *
 * <p> All the abstract methods in this class must be implemented by each
 * cryptographic service provider who wishes to supply the implementation
 * of a key pair generator for a particular algorithm.
 *
 * <p> In case the client does not explicitly initialize the KeyPairGenerator
 * (via a call to an {@code initialize} method), each provider must
 * supply (and document) a default initialization.
 * For example, the <i>Sun</i> provider uses a default modulus size (keysize)
 * of 1024 bits.
 *
 * @author Benjamin Renaud
 *
 *
 * @see KeyPairGenerator
 * @see java.security.spec.AlgorithmParameterSpec
 */

public abstract class KeyPairGeneratorSpi {

    /**
     * Initializes the key pair generator for a certain keysize, using
     * the default parameter set.
     *
     * @param keysize the keysize. This is an
     * algorithm-specific metric, such as modulus length, specified in
     * number of bits.
     *
     * @param random the source of randomness for this generator.
     *
     * @exception InvalidParameterException if the {@code keysize} is not
     * supported by this KeyPairGeneratorSpi object.
     */
    public abstract void initialize(int keysize, SecureRandom random);

    /**
     * Initializes the key pair generator using the specified parameter
     * set and user-provided source of randomness.
     *
     * <p>This concrete method has been added to this previously-defined
     * abstract class. (For backwards compatibility, it cannot be abstract.)
     * It may be overridden by a provider to initialize the key pair
     * generator. Such an override
     * is expected to throw an InvalidAlgorithmParameterException if
     * a parameter is inappropriate for this key pair generator.
     * If this method is not overridden, it always throws an
     * UnsupportedOperationException.
     *
     * @param params the parameter set used to generate the keys.
     *
     * @param random the source of randomness for this generator.
     *
     * @exception InvalidAlgorithmParameterException if the given parameters
     * are inappropriate for this key pair generator.
     *
     * @since 1.2
     */
    public void initialize(AlgorithmParameterSpec params,
                           SecureRandom random)
        throws InvalidAlgorithmParameterException {
            throw new UnsupportedOperationException();
    }

    /**
     * Generates a key pair. Unless an initialization method is called
     * using a KeyPairGenerator interface, algorithm-specific defaults
     * will be used. This will generate a new key pair every time it
     * is called.
     *
     * @return the newly generated {@code KeyPair}
     */
    public abstract KeyPair generateKeyPair();
}

⏎ java/security/KeyPairGeneratorSpi.java

Or download all of them as a single archive file:

File name: jre-rt-java-1.8.0_191-src.zip
File size: 6664831 bytes
Release date: 2018-10-28
Download 

⇒ JRE 8 rt.jar - javax.* Package Source Code

⇐ JRE 8 plugin.jar - Java Deploy Control Panel Plugin

⇑ Download and Use JDK 8

⇑⇑ FAQ for JDK (Java Development Kit)