java加解密RSA使用方法代码示例

时间：2021-11-29 21:21:44

最近为了分析一段请求流，不得不去研究一下RSA加密。

首先，强调一点：密钥的“钥”读“yue”，不是“yao”，额。。。

网上关于RSA的原理一抓一大把的，这里只是简单说说我的理解：

1. 两个足够大的互质数p, q；
2. 用于模运算的模 n=p*q；
3. 公钥KU（e, n）中的e满足 1<e< (p-1)(q-1)，且与(p-1)(q-1)互质；
4. 密钥KR（d, n）中的d满足  d*e % (p-1)(q-1）= 1，%是取余运算。

因为公钥是公开的，所以我知道了e和n，那么根据2,3,4式子的关系，我们只要从n的值推出p, q的值则可计算出d的值，也就能找到密钥。

然而，关键就在这里， n=p*q，如果两个互质数p和q足够大，那么根据目前的计算机技术和其他工具，至今也没能从n分解出p和q，这是数学上的一个难题，也正是这个难题成为了RSA加密至今被广泛使用的原因。换句话说，只要密钥长度n足够大（一般1024足矣），基本上不可能从公钥信息推出私钥信息。

好了，这里作为研究的随笔，记录一下java如何使用，以下主要有三种方法，基本大同小异，只是获取公钥私钥的途径不一样就是了：

方法一：

利用KeyPairGenerator直接生成公钥和密钥，一般私钥保留给服务端，公钥交给客户端。

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public class RSACryptography {
    public static String data="hello world";
    public static void main(String[] args) throws Exception {
        // TODO Auto-generated method stub
        KeyPair keyPair=genKeyPair(1024);
        //获取公钥，并以base64格式打印出来
        PublicKey publicKey=keyPair.getPublic();       
        System.out.println("公钥："+new String(Base64.getEncoder().encode(publicKey.getEncoded())));
        //获取私钥，并以base64格式打印出来
        PrivateKey privateKey=keyPair.getPrivate();    
        System.out.println("私钥："+new String(Base64.getEncoder().encode(privateKey.getEncoded())));
        //公钥加密
        byte[] encryptedBytes=encrypt(data.getBytes(), publicKey); 
        System.out.println("加密后："+new String(encryptedBytes));
        //私钥解密
        byte[] decryptedBytes=decrypt(encryptedBytes, privateKey);     
        System.out.println("解密后："+new String(decryptedBytes));
    }
    //生成密钥对
    public static KeyPair genKeyPair(int keyLength) throws Exception{
        KeyPairGenerator keyPairGenerator=KeyPairGenerator.getInstance("RSA");
        keyPairGenerator.initialize(1024);     
        return keyPairGenerator.generateKeyPair();
    }
    //公钥加密
    public static byte[] encrypt(byte[] content, PublicKey publicKey) throws Exception{
        Cipher cipher=Cipher.getInstance("RSA");//java默认"RSA"="RSA/ECB/PKCS1Padding"
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        return cipher.doFinal(content);
    }
    //私钥解密
    public static byte[] decrypt(byte[] content, PrivateKey privateKey) throws Exception{
        Cipher cipher=Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        return cipher.doFinal(content);
    }
}

运行结果：

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公钥：MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCSl6V7XNkVR9+NotekZm1FjHdL7oDqA66hrG5D/wgQ1XIF22mex7pnNc8PRBRScJQZJbzQ3ZnVmV5XqrVSCGbqaMPFmIXetu6lifQHoGptH9ghZsemanqp0sSd1TkHcPL2Njk/hZabWYBzPbjlidgfcMotehnFUdlIMGCusMV0awIDAQAB
私钥：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
加密后：v?,Y9?檂o庬鉤h﹎m_?$惇櫤?p崃?4蹥bhhN?25/?6T駩樁w草遏鬼碙&柀&*軄Q晛1鱋A祉@眽`剪啃`噾?>x/运婣?HI砛奊瑘i?$B捞
?毟"ST
解密后：hello world

方法二：

实际上，方法一只是用来生成密钥就OK了，生成的密钥需要保存到本地文件中，所以一般不会在客户端调用KeyPairGenerator进行密钥的生成操作。

这里，我们可以将方法一得到的密钥保存到文件，下次我们直接读取就可以了。我假设以String的形式保存在文件内，那么接下来直接使用读取到的String生成密钥即可。

当然，你也可以使用openssl来生成也可以，不过我觉得麻烦就不弄了。

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public class RSACryptography {
    public static String data="hello world";
    public static String publicKeyString="MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCISLP98M/56HexX/9FDM8iuIEQozy6kn2JMcbZS5/BhJ+U4PZIChJfggYlWnd8NWn4BYr2kxxyO8Qgvc8rpRZCkN0OSLqLgZGmNvoSlDw80UXq90ZsVHDTOHuSFHw8Bv//B4evUNJBB8g9tpVxr6P5EJ6FMoR/kY2dVFQCQM4+5QIDAQAB";
    public static String privateKeyString="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";
    public static void main(String[] args) throws Exception {
        // TODO Auto-generated method stub
        //获取公钥
        PublicKey publicKey=getPublicKey(publicKeyString);
        //获取私钥
        PrivateKey privateKey=getPrivateKey(privateKeyString);     
        //公钥加密
        byte[] encryptedBytes=encrypt(data.getBytes(), publicKey); 
        System.out.println("加密后："+new String(encryptedBytes));
        //私钥解密
        byte[] decryptedBytes=decrypt(encryptedBytes, privateKey);     
        System.out.println("解密后："+new String(decryptedBytes));
    }
    //将base64编码后的公钥字符串转成PublicKey实例
    public static PublicKey getPublicKey(String publicKey) throws Exception{
        byte[ ] keyBytes=Base64.getDecoder().decode(publicKey.getBytes());
        X509EncodedKeySpec keySpec=new X509EncodedKeySpec(keyBytes);
        KeyFactory keyFactory=KeyFactory.getInstance("RSA");
        return keyFactory.generatePublic(keySpec); 
    }
    //将base64编码后的私钥字符串转成PrivateKey实例
    public static PrivateKey getPrivateKey(String privateKey) throws Exception{
        byte[ ] keyBytes=Base64.getDecoder().decode(privateKey.getBytes());
        PKCS8EncodedKeySpec keySpec=new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory keyFactory=KeyFactory.getInstance("RSA");
        return keyFactory.generatePrivate(keySpec);
    }
    //公钥加密
    public static byte[] encrypt(byte[] content, PublicKey publicKey) throws Exception{
        Cipher cipher=Cipher.getInstance("RSA");//java默认"RSA"="RSA/ECB/PKCS1Padding"
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        return cipher.doFinal(content);
    }
    //私钥解密
    public static byte[] decrypt(byte[] content, PrivateKey privateKey) throws Exception{
        Cipher cipher=Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        return cipher.doFinal(content);
    }
}

运行结果

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加密后：.a羫閍Q瘿u鉵やAS祏@q??>?:sQ3?A_l'遥`t?6蔍NK%IC尊[鹰#枋リ礼?1i獙 l躕锇仩?"糍>Ij弻脶諾晦5uDq積嬨璼ey冖U'輵\L〥%
解密后：hello world

方法三：

除了保存密钥字符串之外，其他的做法一般是只保存 模n（modulus），公钥和私钥的e和d（exponent）。

其中，n, e, d可以这样获取到，获取到后可以保存到本地文件中。

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//获取公钥
RSAPublicKey publicKey=(RSAPublicKey) getPublicKey(publicKeyString);
BigInteger modulus1=publicKey.getModulus();
BigInteger exponent1=publicKey.getPublicExponent();
   
//获取私钥
RSAPrivateKey privateKey=(RSAPrivateKey) getPrivateKey(privateKeyString);    
BigInteger modulus2=privateKey.getModulus();
BigInteger exponent2=privateKey..getPrivateExponent();

这里，假设我已经从文件中读取到了modulus和exponent：

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public class RSACryptography {
    public static String data="hello world";
    public static String modulusString="95701876885335270857822974167577168764621211406341574477817778908798408856077334510496515211568839843884498881589280440763139683446418982307428928523091367233376499779842840789220784202847513854967218444344438545354682865713417516385450114501727182277555013890267914809715178404671863643421619292274848317157";
    public static String publicExponentString="65537";
    public static String privateExponentString="15118200884902819158506511612629910252530988627643229329521452996670429328272100404155979400725883072214721713247384231857130859555987849975263007110480563992945828011871526769689381461965107692102011772019212674436519765580328720044447875477151172925640047963361834004267745612848169871802590337012858580097";
    public static void main(String[] args) throws Exception {
        // TODO Auto-generated method stub     
        //由n和e获取公钥
        PublicKey publicKey=getPublicKey(modulusString, publicExponentString);
        //由n和d获取私钥
        PrivateKey privateKey=getPrivateKey(modulusString, privateExponentString);
        //公钥加密
        byte[] encryptedBytes=encrypt(data.getBytes(), publicKey); 
        System.out.println("加密后："+new String(encryptedBytes));
        //私钥解密
        byte[] decryptedBytes=decrypt(encryptedBytes, privateKey);     
        System.out.println("解密后："+new String(decryptedBytes));
    }
    //将base64编码后的公钥字符串转成PublicKey实例
    public static PublicKey getPublicKey(String modulusStr, String exponentStr) throws Exception{
        BigInteger modulus=new BigInteger(modulusStr);
        BigInteger exponent=new BigInteger(exponentStr);
        RSAPublicKeySpec publicKeySpec=new RSAPublicKeySpec(modulus, exponent);
        KeyFactory keyFactory=KeyFactory.getInstance("RSA");
        return keyFactory.generatePublic(publicKeySpec);
    }
    //将base64编码后的私钥字符串转成PrivateKey实例
    public static PrivateKey getPrivateKey(String modulusStr, String exponentStr) throws Exception{
        BigInteger modulus=new BigInteger(modulusStr);
        BigInteger exponent=new BigInteger(exponentStr);
        RSAPrivateKeySpec privateKeySpec=new RSAPrivateKeySpec(modulus, exponent);
        KeyFactory keyFactory=KeyFactory.getInstance("RSA");
        return keyFactory.generatePrivate(privateKeySpec);
    }
    //公钥加密
    public static byte[] encrypt(byte[] content, PublicKey publicKey) throws Exception{
        Cipher cipher=Cipher.getInstance("RSA");//java默认"RSA"="RSA/ECB/PKCS1Padding"
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        return cipher.doFinal(content);
    }
    //私钥解密
    public static byte[] decrypt(byte[] content, PrivateKey privateKey) throws Exception{
        Cipher cipher=Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        return cipher.doFinal(content);
    }
}

运行结果：

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加密后：g[>X锽.+?"s謉q琾B?,\??戮陇⒑e*y浌X蜤??眲Z秔豨Wm麞衹靫〩2孲*?X?9赉埤腴暎?~_邊槻U☉疀群廥5z钛?
媷Bdh}>i１运癑障a杽
解密后：hello world

这里三种方式总结起来也就是

1,.KeyPairGenerator获取key；
2. String获取key；
3. modulus和exponent获取key。

--------------------后来，我发现，数据太长抛异常了，好吧---------------------------

然而，当加密的数据太长的时候则需要分组加密，不然数据过长会抛异常，如“Encryt data is too much”，或者“data length is longer than 127”等。

上面三个方法使用的key的n值（modulus）是1024bit的，也就是128byte，根据RSA加密规则，加密1 byte字节的数据，需要12 byte，即其他11byte可能用于记录其他信息什么的，这里我就不清楚了，而1024bit长度的key则最多可以加密128-11=117byte的数据，所以，对于超过117byte的数据，我们需要以117byte为一组进行数据分割。

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public class RSACryptography {
    public static String data="hello world";
    public static String modulusString="95701876885335270857822974167577168764621211406341574477817778908798408856077334510496515211568839843884498881589280440763139683446418982307428928523091367233376499779842840789220784202847513854967218444344438545354682865713417516385450114501727182277555013890267914809715178404671863643421619292274848317157";
    public static String publicExponentString="65537";
    public static String privateExponentString="15118200884902819158506511612629910252530988627643229329521452996670429328272100404155979400725883072214721713247384231857130859555987849975263007110480563992945828011871526769689381461965107692102011772019212674436519765580328720044447875477151172925640047963361834004267745612848169871802590337012858580097";
    public static void main(String[] args) throws Exception {
        // TODO Auto-generated method stub     
        //由n和e获取公钥
        PublicKey publicKey=getPublicKey(modulusString, publicExponentString);
        //由n和d获取私钥
        PrivateKey privateKey=getPrivateKey(modulusString, privateExponentString);
        //公钥加密
        String encrypted=encrypt(data, publicKey); 
        System.out.println("加密后："+encrypted);  
        //私钥解密
        String decrypted=decrypt(encrypted, privateKey);       
        System.out.println("解密后："+new String(decrypted));
    }
    //将base64编码后的公钥字符串转成PublicKey实例
    public static PublicKey getPublicKey(String modulusStr, String exponentStr) throws Exception{
        BigInteger modulus=new BigInteger(modulusStr);
        BigInteger exponent=new BigInteger(exponentStr);
        RSAPublicKeySpec publicKeySpec=new RSAPublicKeySpec(modulus, exponent);
        KeyFactory keyFactory=KeyFactory.getInstance("RSA");
        return keyFactory.generatePublic(publicKeySpec);
    }
    //将base64编码后的私钥字符串转成PrivateKey实例
    public static PrivateKey getPrivateKey(String modulusStr, String exponentStr) throws Exception{
        BigInteger modulus=new BigInteger(modulusStr);
        BigInteger exponent=new BigInteger(exponentStr);
        RSAPrivateKeySpec privateKeySpec=new RSAPrivateKeySpec(modulus, exponent);
        KeyFactory keyFactory=KeyFactory.getInstance("RSA");
        return keyFactory.generatePrivate(privateKeySpec);
    }
    //公钥加密，并转换成十六进制字符串打印出来
    public static String encrypt(String content, PublicKey publicKey) throws Exception{
        Cipher cipher=Cipher.getInstance("RSA");//java默认"RSA"="RSA/ECB/PKCS1Padding"
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        int splitLength=((RSAPublicKey)publicKey).getModulus().bitLength()/8-11;
        byte[][] arrays=splitBytes(content.getBytes(), splitLength);
        StringBuffer sb=new StringBuffer();
        for(byte[] array : arrays){        
            sb.append(bytesToHexString(cipher.doFinal(array)));
        }
        return sb.toString();
    }
    //私钥解密，并转换成十六进制字符串打印出来
    public static String decrypt(String content, PrivateKey privateKey) throws Exception{
        Cipher cipher=Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        int splitLength=((RSAPrivateKey)privateKey).getModulus().bitLength()/8;
        byte[] contentBytes=hexString2Bytes(content);
        byte[][] arrays=splitBytes(contentBytes, splitLength);
        StringBuffer sb=new StringBuffer();
        for(byte[] array : arrays){
            sb.append(new String(cipher.doFinal(array)));
        }
        return sb.toString();
    }
    //拆分byte数组
    public static byte[][] splitBytes(byte[] bytes, int splitLength){
        int x; //商，数据拆分的组数，余数不为0时+1
        int y; //余数
        y=bytes.length%splitLength;
        if(y!=0){
            x=bytes.length/splitLength+1;
        }else{
            x=bytes.length/splitLength;
        }
        byte[][] arrays=new byte[x][];
        byte[] array;
        for(int i=0; i<x; i++){
            if(i==x-1 && bytes.length%splitLength!=0){
                array=new byte[bytes.length%splitLength];
                System.arraycopy(bytes, i*splitLength, array, 0, bytes.length%splitLength);
            }else{
                array=new byte[splitLength];
                System.arraycopy(bytes, i*splitLength, array, 0, splitLength);
            }
            arrays[i]=array;
        }
        return arrays;
    }
    //byte数组转十六进制字符串
    public static String bytesToHexString(byte[] bytes) {
    StringBuffer sb = new StringBuffer(bytes.length);
    String sTemp;
    for (int i = 0; i < bytes.length; i++) {
      sTemp = Integer.toHexString(0xFF & bytes[i]);
      if (sTemp.length() < 2)
        sb.append(0);
      sb.append(sTemp.toUpperCase());
    }
    return sb.toString();
  }
    //十六进制字符串转byte数组
    public static byte[] hexString2Bytes(String hex) {
    int len = (hex.length() / 2);
    hex=hex.toUpperCase();
    byte[] result = new byte[len];
    char[] achar = hex.toCharArray();
    for (int i = 0; i < len; i++) {
      int pos = i * 2;
      result[i] = (byte) (toByte(achar[pos]) << 4 | toByte(achar[pos + 1]));
    }
    return result;
  }
    private static byte toByte(char c) {
    byte b = (byte) "0123456789ABCDEF".indexOf(c);
    return b;
  }
}

运行结果

?
1
2
加密后：0681CEA1051892E038CEB83EDCD5D549B61F31787FEF92123E0961F2E8FAF2590BAD88A2341C9684E6B3791D03D95BDFFF852EFD79B6748364A8A2369828A6E5752FE3910EA162970BAED78ABDE37F2DB2523CB3B47A46A9B2BC2C2C828D6024913B9B52E43837BCD0A6DF74BE14EB593EB732351961EA33732CE5347281EEAE
解密后：hello world

最后，有一点必须强调，因为中间磨了我不少时间。

中间加密后，如果要打印出来，必须以十六进制或者BCD码的形式打印，不能new String（byte[]）后，再从这个String里getbytes（），也不要用base64，不然会破坏原数据。

比如，举个例子：

?
1
2
3
4
5
6
7
byte[ ] bytes=new byte[ ]{108, -56, 111, 34, -67};
byte[ ] newBytes=new String(bytes).getBytes();
StringBuffer sb=new StringBuffer();
for(int i=0; i<newBytes.length; i++){
  sb.append(newBytes[i]+"|");
}
System.out.println(sb.toString());

将一个byte数组new String后再getbytes出来后，看看运行结果：

?
1
108|-56|111|34|63

最后一个byte由-67变为了63，这个务必注意啊~

总结

以上就是本文关于java加解密RSA使用方法代码示例的全部内容，希望对大家有所帮助。有什么问题可以留言指出，欢迎大家交流讨论。

原文链接：http://blog.csdn.net/qq_18870023/article/details/52596808

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