rsa私钥加密java

1. java里面RSA加密算法的使用

RSA的Java实现不能一次加密很大的字符，自己处理了一下，见下面的代码。Base64编码类用的是一个Public domain Base64 for java http://iharder.sourceforge.net/current/java/base64/其他的保存公钥到文件等简单的实现，就不详细说了，看代码吧。==============================================import java.security.*;import java.security.spec.PKCS8EncodedKeySpec;import java.security.spec.X509EncodedKeySpec;import java.util.HashMap;import java.util.Map;import javax.crypto.*;import java.io.*;public class Encryptor {private static final String KEY_FILENAME = "c:\\mykey.dat";private static final String OTHERS_KEY_FILENAME = "c:\\Otherskey.dat";// private static final int KEY_SIZE = 1024;// private static final int BLOCK_SIZE = 117;// private static final int OUTPUT_BLOCK_SIZE = 128;private static final int KEY_SIZE = 2048; //RSA key 是多少位的private static final int BLOCK_SIZE = 245; //一次RSA加密操作所允许的最大长度//这个值与 KEY_SIZE 已经padding方法有关。因为 1024的key的输出是128，2048key输出是256字节//可能11个字节用于保存padding信息了，所以最多可用的就只有245字节了。private static final int OUTPUT_BLOCK_SIZE = 256;private SecureRandom secrand;private Cipher rsaCipher;private KeyPair keys;private Map<String, Key> allUserKeys;public Encryptor() throws Exception {try {allUserKeys = new HashMap<String, Key>();secrand = new SecureRandom();//SunJCE Provider 中只支持ECB mode，试了一下只有PKCS1PADDING可以直接还原原始数据，//NOPadding导致解压出来的都是blocksize长度的数据，还要自己处理//参见 http://java.sun.com/javase/6/docs/technotes/guides/security/SunProviders.html#SunJCEProvider////另外根据 Open-JDK-6.b17-src（ http://www.docjar.com/html/api/com/sun/crypto/provider/RSACipher.java.html）// 中代码的注释，使用RSA来加密大量数据不是一种标准的用法。所以现有实现一次doFinal调用之进行一个RSA操作，//如果用doFinal来加密超过的一个操作所允许的长度数据将抛出异常。//根据keysize的长度，典型的1024个长度的key和PKCS1PADDING一起使用时//一次doFinal调用只能加密117个byte的数据。（NOPadding 和1024 keysize时128个字节长度）//（2048长度的key和PKCS1PADDING 最多允许245字节一次）//想用来加密大量数据的只能自己用其他办法实现了。可能RSA加密速度比较慢吧，要用AES才行rsaCipher = Cipher.getInstance("RSA/ECB/PKCS1PADDING");} catch (NoSuchAlgorithmException e) {e.printStackTrace();} catch (NoSuchPaddingException e) {e.printStackTrace();throw e;}ObjectInputStream in;try {in = new ObjectInputStream(new FileInputStream(KEY_FILENAME));} catch (FileNotFoundException e) {if (false == GenerateKeys()){throw e;}LoadKeys();return;}keys = (KeyPair) in.readObject();in.close();LoadKeys();}/** 生成自己的公钥和私钥*/private Boolean GenerateKeys() {try {KeyPairGenerator keygen = KeyPairGenerator.getInstance("RSA");// secrand = new SecureRandom();// sedSeed之后会造成 生成的密钥都是一样的// secrand.setSeed("chatencrptor".getBytes()); // 初始化随机产生器//key长度至少512长度，不过好像说现在用2048才算比较安全的了keygen.initialize(KEY_SIZE, secrand); // 初始化密钥生成器keys = keygen.generateKeyPair(); // 生成密钥组AddKey("me", EncodeKey(keys.getPublic()));} catch (NoSuchAlgorithmException e) {e.printStackTrace();return false;}ObjectOutputStream out;try {out = new ObjectOutputStream(new FileOutputStream(KEY_FILENAME));} catch (IOException e) {e.printStackTrace();return false;}try {out.writeObject(keys);} catch (IOException e) {e.printStackTrace();return false;} finally {try {out.close();} catch (IOException e) {e.printStackTrace();return false;}}return true;}public String EncryptMessage(String toUser, String Message) throws IOException {Key pubkey = allUserKeys.get(toUser);if ( pubkey == null ){throw new IOException("NoKeyForThisUser") ;}try {//PublicKey pubkey = keys.getPublic();rsaCipher.init(Cipher.ENCRYPT_MODE, pubkey, secrand);//System.out.println(rsaCipher.getBlockSize()); 返回0，非block 加密算法来的？//System.out.println(Message.getBytes("utf-8").length);//byte[] encryptedData = rsaCipher.doFinal(Message.getBytes("utf-8"));byte[] data = Message.getBytes("utf-8");int blocks = data.length / BLOCK_SIZE ;int lastBlockSize = data.length % BLOCK_SIZE ;byte [] encryptedData = new byte[ (lastBlockSize == 0 ? blocks : blocks + 1)* OUTPUT_BLOCK_SIZE];for (int i=0; i < blocks; i++){//int thisBlockSize = ( i + 1 ) * BLOCK_SIZE > data.length ? data.length - i * BLOCK_SIZE : BLOCK_SIZE ;rsaCipher.doFinal(data,i * BLOCK_SIZE, BLOCK_SIZE, encryptedData ,i * OUTPUT_BLOCK_SIZE);}if (lastBlockSize != 0 ){rsaCipher.doFinal(data, blocks * BLOCK_SIZE, lastBlockSize,encryptedData ,blocks * OUTPUT_BLOCK_SIZE);}//System.out.println(encrypted.length); 如果要机密的数据不足128/256字节，加密后补全成为变为256长度的。//数量比较小时，Base64.GZIP产生的长度更长，没什么优势//System.out.println(Base64.encodeBytes(encrypted,Base64.GZIP).length());//System.out.println(Base64.encodeBytes(encrypted).length());//System.out.println (rsaCipher.getOutputSize(30));//这个getOutputSize 只对 输入小于最大的block时才能得到正确的结果。其实就是补全 数据为128/256 字节return Base64.encodeBytes(encryptedData);} catch (InvalidKeyException e) {e.printStackTrace();throw new IOException("InvalidKey") ;}catch (ShortBufferException e) {e.printStackTrace();throw new IOException("ShortBuffer") ;}catch (UnsupportedEncodingException e) {e.printStackTrace();throw new IOException("UnsupportedEncoding") ;} catch (IllegalBlockSizeException e) {e.printStackTrace();throw new IOException("IllegalBlockSize") ;} catch (BadPaddingException e) {e.printStackTrace();throw new IOException("BadPadding") ;}finally {//catch 中 return 或者throw之前都会先调用一下这里}}public String DecryptMessage(String Message) throws IOException {byte[] decoded = Base64.decode(Message);PrivateKey prikey = keys.getPrivate();try {rsaCipher.init(Cipher.DECRYPT_MODE, prikey, secrand);int blocks = decoded.length / OUTPUT_BLOCK_SIZE;ByteArrayOutputStream decodedStream = new ByteArrayOutputStream(decoded.length);for (int i =0 ;i < blocks ; i ++ ){decodedStream.write (rsaCipher.doFinal(decoded,i * OUTPUT_BLOCK_SIZE, OUTPUT_BLOCK_SIZE));}return new String(decodedStream.toByteArray(), "UTF-8");} catch (InvalidKeyException e) {e.printStackTrace();throw new IOException("InvalidKey");} catch (UnsupportedEncodingException e) {e.printStackTrace();throw new IOException("UnsupportedEncoding");} catch (IllegalBlockSizeException e) {e.printStackTrace();throw new IOException("IllegalBlockSize");} catch (BadPaddingException e) {e.printStackTrace();throw new IOException("BadPadding");} finally {// catch 中 return 或者throw之前都会先调用一下这里。}}public boolean AddKey(String user, String key) {PublicKey publickey;try {publickey = DecodePublicKey(key);} catch (Exception e) {return false;}allUserKeys.put(user, publickey);SaveKeys();return true;}private boolean LoadKeys() {BufferedReader input;try {input = new BufferedReader(new InputStreamReader(new FileInputStream(OTHERS_KEY_FILENAME)));} catch (FileNotFoundException e1) {// e1.printStackTrace();return false;}

2. java RSA算法实现256位密钥怎么做

【下载实例】本文介绍RSA2加密与解密，RSA2是RSA的加强版本，在密钥长度上采用2048, RSA2比RSA更安全，更可靠, 本人的另一篇文章RSA已经发表，有想了解的可以点开下面的RSA文章

3. java中RSA用私钥加密公钥解密问题

公钥和私钥可以互换的用，用公钥加密私钥解密，用私钥加密公钥解密都ok，方法一样

4. JAVA写RSA加密，公钥私钥都是一样的，为什么每次加密的结果不一样

肯定会不一样啊，因为加密过程中使用了salt，防止已知密文攻击，你两次加密的结果，用相同的私钥去解密，会得到同样的结果，前提是你的加密算法没写错

5. JAVA写RSA加密，公钥私钥都是一样的，为什么每次加密的结果不一样

RSA 的 PKCS #1 padding 方案在加密前对明文信息进行了随机数填充。 这个博客解析这个的

w屏w蔽w.cnblogs.com/spencerN/archive/2012/10/18/2729602.html

6. Java中RSA的方式如何实现非对称加密的示例

代码如下，需要依赖一个jar包commons-codec-1.9.jar，用于Base64转换，请自行下载。

importorg.apache.commons.codec.binary.Base64;

importjavax.crypto.BadPaddingException;
importjavax.crypto.Cipher;
importjavax.crypto.IllegalBlockSizeException;
importjava.io.ByteArrayOutputStream;
importjava.io.UnsupportedEncodingException;
importjava.security.*;
importjava.security.interfaces.RSAPrivateKey;
importjava.security.interfaces.RSAPublicKey;
importjava.security.spec.PKCS8EncodedKeySpec;
importjava.security.spec.X509EncodedKeySpec;

publicclassRSAUtils{

//加密方式
="RSA";
//签名算法
_ALGORITHM="SHA1WithRSA";
//创建密钥对初始长度
privatestaticfinalintKEY_SIZE=512;
//字符编码格式
="UTF-8";
//RSA最大加密明文大小
privatestaticfinalintMAX_ENCRYPT_BLOCK=117;
//RSA最大解密密文大小
privatestaticfinalintMAX_DECRYPT_BLOCK=128;

privateKeyFactorykeyFactory;

publicRSAUtils(){
keyFactory=KeyFactory.getInstance(ALGORITHM);
}

/**
*私钥加密
*
*@paramcontent待加密字符串
*@paramprivateKey私钥
*@return加密后字符串（BASE64编码）
*/
(Stringcontent,StringprivateKey)throwsException{
Stringresult;

try(ByteArrayOutputStreamout=newByteArrayOutputStream()){
byte[]keyBytes=newBase64().decode(privateKey);
=newPKCS8EncodedKeySpec(keyBytes);
PrivateKeypKey=keyFactory.generatePrivate(pkcs8KeySpec);
Ciphercipher=Cipher.getInstance(ALGORITHM);
cipher.init(Cipher.ENCRYPT_MODE,pKey);

byte[]data=content.getBytes(CHARSET);
write2Stream(cipher,data,out);
byte[]resultBytes=out.toByteArray();

result=Base64.encodeBase64String(resultBytes);
}catch(Exceptione){
thrownewException(e);
}

returnresult;
}

/**
*公钥解密
*
*@paramcontent已加密字符串（BASE64加密）
*@parampublicKey公钥
*@return
*/
(Stringcontent,StringpublicKey)throwsException{
Stringresult="";

try(ByteArrayOutputStreamout=newByteArrayOutputStream()){
byte[]keyBytes=newBase64().decode(publicKey);
X509EncodedKeySpecx509KeySpec=newX509EncodedKeySpec(keyBytes);
PublicKeypKey=keyFactory.generatePublic(x509KeySpec);
Ciphercipher=Cipher.getInstance(ALGORITHM);
cipher.init(Cipher.DECRYPT_MODE,pKey);

byte[]data=Base64.decodeBase64(content);
write2Stream(cipher,data,out);
byte[]resultBytes=out.toByteArray();

result=newString(resultBytes);
}catch(Exceptione){
thrownewException(e);
}

returnresult;
}

/**
*公钥加密
*
*@paramcontent待加密字符串
*@parampublicKey公钥
*@return加密后字符串（BASE64编码）
*/
(Stringcontent,StringpublicKey)throwsException{
Stringresult="";

try(ByteArrayOutputStreamout=newByteArrayOutputStream()){
byte[]keyBytes=newBase64().decode(publicKey);
X509EncodedKeySpecx509KeySpec=newX509EncodedKeySpec(keyBytes);
PublicKeypKey=keyFactory.generatePublic(x509KeySpec);
Ciphercipher=Cipher.getInstance(ALGORITHM);
cipher.init(Cipher.ENCRYPT_MODE,pKey);

byte[]data=content.getBytes(CHARSET);
write2Stream(cipher,
data,out);
byte[]resultBytes=out.toByteArray();
result=Base64.encodeBase64String(resultBytes);
}catch(Exceptione){
thrownewException(e);
}

returnresult;
}

/**
*私钥解密
*
*@paramcontent已加密字符串
*@paramprivateKey私钥
*@return解密后字符串
*/
(Stringcontent,StringprivateKey)throwsException{
Stringresult="";

try(ByteArrayOutputStreamout=newByteArrayOutputStream()){
byte[]keyBytes=newBase64().decode(privateKey);
=newPKCS8EncodedKeySpec(keyBytes);
PrivateKeypKey=keyFactory.generatePrivate(pkcs8KeySpec);
Ciphercipher=Cipher.getInstance(ALGORITHM);
cipher.init(Cipher.DECRYPT_MODE,pKey);

byte[]data=Base64.decodeBase64(content);
write2Stream(cipher,data,out);
byte[]resultBytes=out.toByteArray();
result=newString(resultBytes);
}catch(Exceptione){
thrownewException(e);
}

returnresult;
}

privatestaticvoidwrite2Stream(Ciphercipher,byte[]data,ByteArrayOutputStreamout)throws
BadPaddingException,IllegalBlockSizeException{
intdataLen=data.length;
intoffSet=0;
byte[]cache;
inti=0;
//对数据分段解密
while(dataLen-offSet>0){
if(dataLen-offSet>MAX_DECRYPT_BLOCK){
cache=cipher.doFinal(data,offSet,MAX_DECRYPT_BLOCK);
}else{
cache=cipher.doFinal(data,offSet,dataLen-offSet);
}
out.write(cache,0,cache.length);
i++;
offSet=i*MAX_DECRYPT_BLOCK;
}
}

/**
*用私钥对信息生成数字签名
*
*@paramdata已加密数据
*@paramprivateKey私钥(BASE64编码)
*@returnsign
*/
publicStringsign(Stringdata,StringprivateKey)throwsException{
Stringresult="";
try{
byte[]keyBytes=newBase64().decode(privateKey);
=newPKCS8EncodedKeySpec(keyBytes);
PrivateKeyprivateK=keyFactory.generatePrivate(pkcs8KeySpec);
Signaturesignature=Signature.getInstance(SIGNATURE_ALGORITHM);
signature.initSign(privateK);
signature.update(parse2HexStr(data).getBytes(CHARSET));

result=newBase64().encodeToString(signature.sign());
}catch(Exceptione){
thrownewException(e);
}
returnresult;
}

/**
*校验数字签名
*
*@paramdata已加密数据
*@parampublicKey公钥(BASE64编码)
*@paramsign数字签名
*@return
*@throwsException
*/
publicbooleanverify(Stringdata,StringpublicKey,Stringsign)throwsException{
booleanresult;

try{
byte[]keyBytes=newBase64().decode(publicKey);
X509EncodedKeySpeckeySpec=newX509EncodedKeySpec(keyBytes);
PublicKeypublicK=keyFactory.generatePublic(keySpec);
Signaturesignature=Signature.getInstance(SIGNATURE_ALGORITHM);
signature.initVerify(publicK);
signature.update(parse2HexStr(data).getBytes(CHARSET));
result=signature.verify(newBase64().decode(sign));
}catch(Exceptione){
thrownewException(e);
}
returnresult;
}

/**
*将二进制转换成16进制
*
*@paramdata
*@return
*/
(Stringdata)throwsException{
Stringresult="";
try{
byte[]buf=data.getBytes(CHARSET);

StringBuffersb=newStringBuffer();
for(inti=0;i<buf.length;i++){
Stringhex=Integer.toHexString(buf[i]&0xFF);
if(hex.length()==1){
hex='0'+hex;
}
sb.append(hex.toUpperCase());
}
result=sb.toString();
}catch(UnsupportedEncodingExceptione){
thrownewException(e);
}
returnresult;
}

/**
*生成公钥与私钥
*/
publicstaticvoidcreateKey()throwsException{
try{
=KeyPairGenerator.getInstance(ALGORITHM);
keyPairGenerator.initialize(KEY_SIZE);
KeyPairkeyPair=keyPairGenerator.generateKeyPair();
RSAPublicKeyrsaPublicKey=(RSAPublicKey)keyPair.getPublic();
RSAPrivateKeyrsaPrivateKey=(RSAPrivateKey)keyPair.getPrivate();

StringpublicKey=Base64.encodeBase64String(rsaPublicKey.getEncoded());
StringprivateKey=Base64.encodeBase64String(rsaPrivateKey.getEncoded());

System.out.println("publicKey="+publicKey+"
privateKey="+privateKey);
}catch(NoSuchAlgorithmExceptione){
thrownewException(e);
}
}

publicstaticvoidmain(String[]args)throwsException{

StringPRIVATE_KEY="+m+/fNs1bmgfJhI8lhr/o/Hy8EFB/I/DDyLcCcU4bCLtxpki8edC+KJR2WvyYfnVmWEe//++W5C+lesEOAqdO5nahRZsL8BIDoxTEn2j+DSa///1qX+t8f5wD8i/8GU702PeCwkGI5ymrARq+/+/nkefTq0SNpUDVbGxVpJi9/FOUf";
StringPUBLIC_KEY="+lc///NfOvKvQndzDH60DzLGOMdE0NBrTn/5zEjGwJbVdlvCfOiHwIDAQAB";

RSAUtilsrsaUtil=newRSAUtils();
StringencryptByPublicKey=rsaUtil.encryptByPublicKey("你好！",PUBLIC_KEY);
System.out.println(encryptByPublicKey);
StringdecryptByPrivateKey=rsaUtil.decryptByPrivateKey(encryptByPublicKey,PRIVATE_KEY);
System.out.println(decryptByPrivateKey);
StringencryptByPrivateKey=rsaUtil.encryptByPrivateKey("你好！",PRIVATE_KEY);
System.out.println(encryptByPrivateKey);
StringdecryptByPublicKey=rsaUtil.decryptByPublicKey(encryptByPrivateKey,PUBLIC_KEY);
System.out.println(decryptByPublicKey);
Stringsign=rsaUtil.sign("1234",PRIVATE_KEY);
System.out.println("sign:"+sign);
System.out.println(rsaUtil.verify("1234",PUBLIC_KEY,sign));
}
}

7. java rsa私钥加密

java rsa私钥加密是什么？让我们一起来了解一下吧！

java rsa私钥加密是一种加密算法。私钥加密算法是用私钥来进行加密与解密信息。私钥加密也被称作对称加密，原因是加密与解密使用的秘钥是同一个。

RSA加密需要注意的事项如下：

1. 首先产生公钥与私钥

2. 设计加密与解密的算法

3. 私钥加密的数据信息只能由公钥可以解密

4. 公钥加密的数据信息只能由私钥可以解密

实战演练，具体步骤如下： public class RsaCryptTools {     private static final String CHARSET = "utf-8";     private static final Base64.Decoder decoder64 = Base64.getDecoder();     private static final Base64.Encoder encoder64 = Base64.getEncoder();       /**      * 生成公私钥      * @param keySize      * @return      * @throws NoSuchAlgorithmException      */     public static SecretKey generateSecretKey(int keySize) throws NoSuchAlgorithmException {         //生成密钥对         KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");         keyGen.initialize(keySize, new SecureRandom());         KeyPair pair = keyGen.generateKeyPair();         PrivateKey privateKey = pair.getPrivate();         PublicKey publicKey = pair.getPublic();         //这里可以将密钥对保存到本地         return new SecretKey(encoder64.encodeToString(publicKey.getEncoded()), encoder64.encodeToString(privateKey.getEncoded()));     }     /**      * 私钥加密      * @param data      * @param privateInfoStr      * @return      * @throws IOException      * @throws InvalidCipherTextException      */     public static String encryptData(String data, String privateInfoStr) throws IOException, InvalidKeySpecException, NoSuchAlgorithmException, InvalidKeyException, NoSuchPaddingException, BadPaddingException, IllegalBlockSizeException {           Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");         cipher.init(Cipher.ENCRYPT_MODE, getPrivateKey(privateInfoStr));         return encoder64.encodeToString(cipher.doFinal(data.getBytes(CHARSET)));     }       /**      * 公钥解密      * @param data      * @param publicInfoStr      * @return      */     public static String decryptData(String data, String publicInfoStr) throws NoSuchPaddingException, NoSuchAlgorithmException, InvalidKeySpecException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException, UnsupportedEncodingException {         byte[] encryptDataBytes=decoder64.decode(data.getBytes(CHARSET));         //解密         Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");         cipher.init(Cipher.DECRYPT_MODE, getPublicKey(publicInfoStr));         return new String(cipher.doFinal(encryptDataBytes), CHARSET);     }     private static PublicKey getPublicKey(String base64PublicKey) throws NoSuchAlgorithmException, InvalidKeySpecException {         X509EncodedKeySpec keySpec = new X509EncodedKeySpec(Base64.getDecoder().decode(base64PublicKey.getBytes()));         KeyFactory keyFactory = KeyFactory.getInstance("RSA");         return keyFactory.generatePublic(keySpec);     }     private static PrivateKey getPrivateKey(String base64PrivateKey) throws NoSuchAlgorithmException, InvalidKeySpecException {         PrivateKey privateKey = null;         PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(Base64.getDecoder().decode(base64PrivateKey.getBytes()));         KeyFactory keyFactory = null;         keyFactory = KeyFactory.getInstance("RSA");         privateKey = keyFactory.generatePrivate(keySpec);         return privateKey;     }       /**      * 密钥实体      * @author hank      * @since 2020/2/28 0028 下午 16:27      */     public static class SecretKey {         /**          * 公钥          */         private String publicKey;         /**          * 私钥          */         private String privateKey;           public SecretKey(String publicKey, String privateKey) {             this.publicKey = publicKey;             this.privateKey = privateKey;         }           public String getPublicKey() {             return publicKey;         }           public void setPublicKey(String publicKey) {             this.publicKey = publicKey;         }           public String getPrivateKey() {             return privateKey;         }           public void setPrivateKey(String privateKey) {             this.privateKey = privateKey;         }           @Override         public String toString() {             return "SecretKey{" +                     "publicKey='" + publicKey + '\'' +                     ", privateKey='" + privateKey + '\'' +                     '}';         }     }       private static void writeToFile(String path, byte[] key) throws IOException {         File f = new File(path);         f.getParentFile().mkdirs();           try(FileOutputStream fos = new FileOutputStream(f)) {             fos.write(key);             fos.flush();         }     }       public static void main(String[] args) throws NoSuchAlgorithmException, NoSuchPaddingException, IOException, BadPaddingException, IllegalBlockSizeException, InvalidKeyException, InvalidKeySpecException {         SecretKey secretKey = generateSecretKey(2048);         System.out.println(secretKey);         String enStr = encryptData("你好测试测试", secretKey.getPrivateKey());         System.out.println(enStr);         String deStr = decryptData(enStr, secretKey.getPublicKey());         System.out.println(deStr);         enStr = encryptData("你好测试测试hello", secretKey.getPrivateKey());         System.out.println(enStr);         deStr = decryptData(enStr, secretKey.getPublicKey());         System.out.println(deStr);     }   }

8. java 中的Cipher类RSA方式能不能用私钥加密公钥解密，完整解释下

KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
keyGen.initialize(1024);
KeyPair key = keyGen.generateKeyPair();

Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
//把第二个参数改为 key.getPrivate()
cipher.init(Cipher.ENCRYPT_MODE, key.getPublic());
byte[] cipherText = cipher.doFinal("Message".getBytes("UTF8"));
System.out.println(new String(cipherText, "UTF8"));
//把第二个参数改为key.getPublic()
cipher.init(Cipher.DECRYPT_MODE, key.getPrivate());
byte[] newPlainText = cipher.doFinal(cipherText);
System.out.println(new String(newPlainText, "UTF8"));

正常的用公钥加密私钥解密就是这个过程，如果按私钥加密公钥解密，只要按备注改2个参数就可以。

但是我要提醒楼主，你要公钥解密，公钥是公开的，相当于任何人都查到公钥可以解密。
你是想做签名是吧。

9. JAVA写RSA加密，公钥私钥都是一样的，为什么每次加密的结果不一样

因为rsa是非对称加密，它使用的是随机大素数的抽取，每次随机生成的，所以每次加密的结果不可能一样

10. JAVA写RSA加密，公钥私钥都是一样的，为什么每次加密的结果不一样

http://blog.csdn.net/defonds/article/details/42775183
这个博客写的很好。