公钥加密也称为非对称加密、速度慢、加密和解密的钥匙不相同，某一个人持有私钥，任何人都可以知道公钥

import java.security.KeyPair;  
import java.security.KeyPairGenerator;  
import java.security.PrivateKey;  
import java.security.PublicKey;  
import java.util.Arrays;  
  
import javax.crypto.Cipher;  
  
/** 
 * RSA算法 公钥加密 非对称加密 
 * @author stone 
 * @date 2014-03-11 00:28:38 
 */  
public class RSA {  
    public static final String KEY_ALGORITHM = "RSA";  
    public static final String CIPHER_ALGORITHM_ECB1 = "RSA/ECB/PKCS1Padding";  
    public static final String CIPHER_ALGORITHM_ECB2 = "RSA/ECB/OAEPWithSHA-1AndMGF1Padding"; //不能用  
    public static final String CIPHER_ALGORITHM_ECB3 = "OAEPWithSHA-256AndMGF1Padding"; //不能用  
      
    static PublicKey publicKey;  
    static PrivateKey privateKey;  
    static Cipher cipher;  
    static KeyPair keyPair;  
      
    public static void main(String[] args) throws Exception {  
        method1("斯柯达U*(Sfsad7f()*^%%$");  
        method2("斯柯达U*(Sfsad7f()*^%%$");  
        method3("斯柯达U*(Sfsad7f()*^%%$");  
          
    }  
      
    /** 
     * 公钥加密，私钥解密    使用默认CIPHER_ALGORITHM_ECB1 
     * @param str 
     * @throws Exception 
     */  
    static void method1(String str) throws Exception {  
        KeyPairGenerator keyGenerator = KeyPairGenerator.getInstance(KEY_ALGORITHM);  
        KeyPair keyPair = keyGenerator.generateKeyPair();  
        publicKey = keyPair.getPublic();  
        privateKey = keyPair.getPrivate();  
        cipher = Cipher.getInstance(KEY_ALGORITHM);  
        cipher.init(Cipher.ENCRYPT_MODE, publicKey); //公钥加密  
        byte[] encrypt = cipher.doFinal(str.getBytes());  
        System.out.println("公钥加密后1：" + Arrays.toString(encrypt));  
          
        cipher.init(Cipher.DECRYPT_MODE, privateKey);//私钥解密  
        byte[] decrypt = cipher.doFinal(encrypt);  
        System.out.println("私钥解密后1：" + new String(decrypt));  
    }  
      
    /** 
     * 私钥加密，公钥解密    使用默认CIPHER_ALGORITHM_ECB1 
     * @param str 
     * @throws Exception 
     */  
    static void method2(String str) throws Exception {  
        KeyPairGenerator keyGenerator = KeyPairGenerator.getInstance(KEY_ALGORITHM);  
        KeyPair keyPair = keyGenerator.generateKeyPair();  
        publicKey = keyPair.getPublic();  
        privateKey = keyPair.getPrivate();  
        cipher = Cipher.getInstance(KEY_ALGORITHM);  
        cipher.init(Cipher.ENCRYPT_MODE, privateKey); //私钥加密  
        byte[] encrypt = cipher.doFinal(str.getBytes());  
        System.out.println("私钥加密后2：" + Arrays.toString(encrypt));  
          
        cipher.init(Cipher.DECRYPT_MODE, publicKey);//公钥解密  
        byte[] decrypt = cipher.doFinal(encrypt);  
        System.out.println("公钥解密后2：" + new String(decrypt));  
    }  
      
    /** 
     * 私钥加密，公钥解密    使用CIPHER_ALGORITHM_ECB1 = RSA/ECB/PKCS1Padding 
     * @param str 
     * @throws Exception 
     */  
    static void method3(String str) throws Exception {  
        KeyPairGenerator keyGenerator = KeyPairGenerator.getInstance(KEY_ALGORITHM);  
        KeyPair keyPair = keyGenerator.generateKeyPair();  
        publicKey = keyPair.getPublic();  
        privateKey = keyPair.getPrivate();  
        cipher = Cipher.getInstance(CIPHER_ALGORITHM_ECB1);  
        cipher.init(Cipher.ENCRYPT_MODE, privateKey); //私钥加密  
        byte[] encrypt = cipher.doFinal(str.getBytes());  
        System.out.println("私钥加密后3：" + Arrays.toString(encrypt));  
          
        cipher.init(Cipher.DECRYPT_MODE, publicKey);//公钥解密  
        byte[] decrypt = cipher.doFinal(encrypt);  
        System.out.println("公钥解密后3：" + new String(decrypt));  
    }  
}