概述
RSA被称为非对称性加密算法，意思就是加密和解密用的不是同一份密钥。RSA算法的密钥分为公钥和私钥，两者内容不同，用途也不同。公钥用于加密，一般交给客户端使用；私钥用于解密，一般由服务器管理。反过来，对称性加密算法，指的就是用同一份密钥进行加密解密了，比如DES加密算法。
RSA算法实现
一、生成密钥对
在使用RSA加密解密之前，首先要生成密钥对。RSA算法的密钥可以通过两个途径生成，一是借助openssl命令终端，二是使用代码生成。
1、Openssl生成密钥对
首先你得安装Openssl，这里就不再叙述如何安装Openssl了，正好给你个机会去撩一下度娘。
第一步，生成私钥。现在我们找到openssl安装目录的bin文件夹，双击打开openssl.exe，输入命令
genrsa -out rsa_private_key.pem 1024
在openssl.exe的同级目录下可以找到生成的私钥文件rsa_private_key.pem，打开后看到的内容类似下面
-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
请忽略带有虚线的第一行和最后一行，中间的内容就是我们的私钥了。
第二步，生成公钥。继续在openssl终端窗口输入命令：
rsa -in rsa_private_key.pem -out rsa_public_key.pem -pubout
这里根据私钥数据，生成了公钥，同样也是保存在openssl.exe同级目录下，打开看里面的内容：
-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC7yil5BUsHf+PdPl9fzdr3FNyr
XDPJwV8Vfk3hCsiqs3YzHYjEYpHZiaF8dg9wB/aqmKRA0KFH2eTv++GNf0fAtdfb
ZUeq1Y79BDs23kSoS6g0Xe8mD76A2oD+G0o/llsBjpmWViFaCre0uALyOwd412pU
7yj+IJU+JlNlxLapNwIDAQAB
-----END PUBLIC KEY-----
到这里，密钥对基本生成了，但是这个密钥对的私钥无法在代码中直接使用，需要对私钥进行PKCS#8编码，继续敲命令：
pkcs8 -topk8 -in rsa_private_key.pem -out pkcs8_rsa_private_key.pem -nocrypt
同样在openssl.exe同级目录下找到文件pkcs8_rsa_private_key.pem，这里就是我们最终需要的私钥了。
下面可以看到内容跟rsa_private_key.pem里面的内容是不一样的：
-----BEGIN PRIVATE KEY-----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-----END PRIVATE KEY-----
2、代码生成密钥对
除了上面的openssl方法可以生成密钥对外，使用代码也是可以生成的，具体的代码如下：
public static KeyPair generateRSAKeyPair(int keyLength)
{
try
{
KeyPairGenerator kpg = KeyPairGenerator.getInstance(RSA);
kpg.initialize(keyLength);
return kpg.genKeyPair();
} catch (NoSuchAlgorithmException e)
{
e.printStackTrace();
return null;
}
}
keyLength范围512~2048， 一般取1024，其他值本人没尝试过，有探索精神的可以自行更改。
通过keyPair.getPublic().getEncoded()，keyPair.getPrivate().getEncoded()分别获取公钥、私钥的字节码。
为了更直观一点，可以通过Base64编码把字节码转为可读的字符串保存起来 Base64Utils.encode(rsaKeyPair.getPublic().getEncoded());
二、RSA加密解密代码实现
废话少说，赶着回家吃饭，上代码：
package com.yspay.sdk.util;
import java.io.BufferedReader;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.math.BigInteger;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.RSAPublicKeySpec;
import java.security.spec.X509EncodedKeySpec;
import javax.crypto.Cipher;
/**
*
*/
public final class RSAUtils
{
private static String RSA = "RSA";
/**
* 随机生成RSA密钥对(默认密钥长度为1024)
*
* @return
*/
public static KeyPair generateRSAKeyPair()
{
return generateRSAKeyPair(1024);
}
/**
* 随机生成RSA密钥对
*
* @param keyLength
* 密钥长度，范围：512～2048<br>
* 一般1024
* @return
*/
public static KeyPair generateRSAKeyPair(int keyLength)
{
try
{
KeyPairGenerator kpg = KeyPairGenerator.getInstance(RSA);
kpg.initialize(keyLength);
return kpg.genKeyPair();
} catch (NoSuchAlgorithmException e)
{
e.printStackTrace();
return null;
}
}
/**
* 用公钥加密 <br>
* 每次加密的字节数，不能超过密钥的长度值除以 8 再减去 11，所以采取分段加密的方式规避
*
* @param data 需加密数据的byte数据
* @param publicKey 公钥
* @return 加密后的byte型数据
*/
public static byte[] encryptData(byte[] data, PublicKey publicKey)
{
try
{
Cipher cipher = Cipher.getInstance(RSA);
// 编码前设定编码方式及密钥
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
RSAPublicKey rsaPublicKey = (RSAPublicKey) publicKey;
// 模长
int keyLen = rsaPublicKey.getModulus().bitLength() / 8;
int maxEncryptBlock = keyLen - 11;
//如果明文长度大于模长-11则要分组加密
int inputLen = data.length;
ByteArrayOutputStream out = new ByteArrayOutputStream();
int offSet = 0;
byte[] temp;
int i = 0;
// 对数据分段加密
while (inputLen - offSet > 0) {
if (inputLen - offSet > maxEncryptBlock) {
temp = cipher.doFinal(data, offSet, maxEncryptBlock);
} else {
temp = cipher.doFinal(data, offSet, inputLen - offSet);
}
out.write(temp, 0, temp.length);
i++;
offSet = i * maxEncryptBlock;
}
byte[] encryptedData = out.toByteArray();
out.close();
// 传入编码数据并返回编码结果
return encryptedData;
} catch (Exception e)
{
e.printStackTrace();
return null;
}
}
/**
* 用私钥解密
*
* @param encryptedData 经过encryptedData()加密返回的byte数据
* @param privateKey 私钥
* @return
*/
public static byte[] decryptData(byte[] encryptedData, PrivateKey privateKey)
{
try
{
Cipher cipher = Cipher.getInstance(RSA);
cipher.init(Cipher.DECRYPT_MODE, privateKey);
RSAPrivateKey rsaPrivateKey = (RSAPrivateKey) privateKey;
// 模长
int keyLen = rsaPrivateKey.getModulus().bitLength() / 8;
int maxDecryptBlock = keyLen;//不用减11
//如果密文长度大于模长则要分组解密
int inputLen = encryptedData.length;
ByteArrayOutputStream out = new ByteArrayOutputStream();
int offSet = 0;
byte[] temp;
int i = 0;
// 对数据分段解密
while (inputLen - offSet > 0) {
if (inputLen - offSet > maxDecryptBlock) {
temp = cipher.doFinal(encryptedData, offSet, maxDecryptBlock);
} else {
temp = cipher.doFinal(encryptedData, offSet, inputLen - offSet);
}
out.write(temp, 0, temp.length);
i++;
offSet = i * maxDecryptBlock;
}
byte[] decryptedData = out.toByteArray();
out.close();
return decryptedData;
} catch (Exception e)
{
e.printStackTrace();
return null;
}
}
/**
* 通过公钥byte[](publicKey.getEncoded())将公钥还原，适用于RSA算法
*
* @param keyBytes
* @return
* @throws NoSuchAlgorithmException
* @throws InvalidKeySpecException
*/
public static PublicKey getPublicKey(byte[] keyBytes) throws NoSuchAlgorithmException,
InvalidKeySpecException
{
X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);
KeyFactory keyFactory = KeyFactory.getInstance(RSA);
PublicKey publicKey = keyFactory.generatePublic(keySpec);
return publicKey;
}
/**
* 通过私钥byte[]将公钥还原，适用于RSA算法
*
* @param keyBytes
* @return
* @throws NoSuchAlgorithmException
* @throws InvalidKeySpecException
*/
public static PrivateKey getPrivateKey(byte[] keyBytes) throws NoSuchAlgorithmException,
InvalidKeySpecException
{
PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(keyBytes);
KeyFactory keyFactory = KeyFactory.getInstance(RSA);
PrivateKey privateKey = keyFactory.generatePrivate(keySpec);
return privateKey;
}
/**
* 使用N、e值还原公钥
*
* @param modulus
* @param publicExponent
* @return
* @throws NoSuchAlgorithmException
* @throws InvalidKeySpecException
*/
public static PublicKey getPublicKey(String modulus, String publicExponent)
throws NoSuchAlgorithmException, InvalidKeySpecException
{
BigInteger bigIntModulus = new BigInteger(modulus);
BigInteger bigIntPrivateExponent = new BigInteger(publicExponent);
RSAPublicKeySpec keySpec = new RSAPublicKeySpec(bigIntModulus, bigIntPrivateExponent);
KeyFactory keyFactory = KeyFactory.getInstance(RSA);
PublicKey publicKey = keyFactory.generatePublic(keySpec);
return publicKey;
}
/**
* 使用N、d值还原私钥
*
* @param modulus
* @param privateExponent
* @return
* @throws NoSuchAlgorithmException
* @throws InvalidKeySpecException
*/
public static PrivateKey getPrivateKey(String modulus, String privateExponent)
throws NoSuchAlgorithmException, InvalidKeySpecException
{
BigInteger bigIntModulus = new BigInteger(modulus);
BigInteger bigIntPrivateExponent = new BigInteger(privateExponent);
RSAPublicKeySpec keySpec = new RSAPublicKeySpec(bigIntModulus, bigIntPrivateExponent);
KeyFactory keyFactory = KeyFactory.getInstance(RSA);
PrivateKey privateKey = keyFactory.generatePrivate(keySpec);
return privateKey;
}
/**
* 从字符串中加载公钥
*
* @param publicKeyStr
* 公钥数据字符串
* @throws Exception
* 加载公钥时产生的异常
*/
public static PublicKey loadPublicKey(String publicKeyStr) throws Exception
{
try
{
byte[] buffer = Base64Utils.decode(publicKeyStr);
KeyFactory keyFactory = KeyFactory.getInstance(RSA);
X509EncodedKeySpec keySpec = new X509EncodedKeySpec(buffer);
return (RSAPublicKey) keyFactory.generatePublic(keySpec);
} catch (NoSuchAlgorithmException e)
{
throw new Exception("无此算法");
} catch (InvalidKeySpecException e)
{
throw new Exception("公钥非法");
} catch (NullPointerException e)
{
throw new Exception("公钥数据为空");
}
}
/**
* 从字符串中加载私钥<br>
* 加载时使用的是PKCS8EncodedKeySpec（PKCS#8编码的Key指令）。
*
* @param privateKeyStr
* @return
* @throws Exception
*/
public static PrivateKey loadPrivateKey(String privateKeyStr) throws Exception
{
try
{
byte[] buffer = Base64Utils.decode(privateKeyStr);
//X509EncodedKeySpec keySpec = new X509EncodedKeySpec(buffer);
PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(buffer);
KeyFactory keyFactory = KeyFactory.getInstance(RSA);
return (RSAPrivateKey) keyFactory.generatePrivate(keySpec);
} catch (NoSuchAlgorithmException e)
{
throw new Exception("无此算法");
} catch (InvalidKeySpecException e)
{
throw new Exception("私钥非法");
} catch (NullPointerException e)
{
throw new Exception("私钥数据为空");
}
}
/**
* 从文件中输入流中加载公钥
*
* @param in
* 公钥输入流
* @throws Exception
* 加载公钥时产生的异常
*/
public static PublicKey loadPublicKey(InputStream in) throws Exception
{
try
{
return loadPublicKey(readKey(in));
} catch (IOException e)
{
throw new Exception("公钥数据流读取错误");
} catch (NullPointerException e)
{
throw new Exception("公钥输入流为空");
}
}
/**
* 从文件中加载私钥
* @param in
* @return 私钥
* @throws Exception
*/
public static PrivateKey loadPrivateKey(InputStream in) throws Exception
{
try
{
return loadPrivateKey(readKey(in));
} catch (IOException e)
{
throw new Exception("私钥数据读取错误");
} catch (NullPointerException e)
{
throw new Exception("私钥输入流为空");
}
}
/**
* 读取密钥信息
*
* @param in
* @return
* @throws IOException
*/
private static String readKey(InputStream in) throws IOException
{
BufferedReader br = new BufferedReader(new InputStreamReader(in));
String readLine = null;
StringBuilder sb = new StringBuilder();
while ((readLine = br.readLine()) != null)
{
if (readLine.charAt(0) == '-')
{
continue;
} else
{
sb.append(readLine);
sb.append('\r');
}
}
return sb.toString();
}
}
Base64编码工具可以使用系统自带的android.util.Base64，也可以自己实现，以下是 从别处扣来的代码：
package com.yspay.sdk.util;
import java.io.UnsupportedEncodingException;
/**
* Created by MPC on 2017/5/24.
*/
public class Base64Utils {
private static char[] base64EncodeChars = new char[]
{ 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5',
'6', '7', '8', '9', '+', '/' };
private static byte[] base64DecodeChars = new byte[]
{ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53,
54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,
12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29,
30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1,
-1, -1, -1 };
/**
* 加密
*
* @param data
* @return
*/
public static String encode(byte[] data)
{
StringBuffer sb = new StringBuffer();
int len = data.length;
int i = 0;
int b1, b2, b3;
while (i < len)
{
b1 = data[i++] & 0xff;
if (i == len)
{
sb.append(base64EncodeChars[b1 >>> 2]);
sb.append(base64EncodeChars[(b1 & 0x3) << 4]);
sb.append("==");
break;
}
b2 = data[i++] & 0xff;
if (i == len)
{
sb.append(base64EncodeChars[b1 >>> 2]);
sb.append(base64EncodeChars[((b1 & 0x03) << 4) | ((b2 & 0xf0) >>> 4)]);
sb.append(base64EncodeChars[(b2 & 0x0f) << 2]);
sb.append("=");
break;
}
b3 = data[i++] & 0xff;
sb.append(base64EncodeChars[b1 >>> 2]);
sb.append(base64EncodeChars[((b1 & 0x03) << 4) | ((b2 & 0xf0) >>> 4)]);
sb.append(base64EncodeChars[((b2 & 0x0f) << 2) | ((b3 & 0xc0) >>> 6)]);
sb.append(base64EncodeChars[b3 & 0x3f]);
}
return sb.toString();
}
/**
* 解密
*
* @param str
* @return
*/
public static byte[] decode(String str)
{
try
{
return decodePrivate(str);
} catch (UnsupportedEncodingException e)
{
e.printStackTrace();
}
return new byte[]
{};
}
private static byte[] decodePrivate(String str) throws UnsupportedEncodingException
{
StringBuffer sb = new StringBuffer();
byte[] data = null;
data = str.getBytes("US-ASCII");
int len = data.length;
int i = 0;
int b1, b2, b3, b4;
while (i < len)
{
do
{
b1 = base64DecodeChars[data[i++]];
} while (i < len && b1 == -1);
if (b1 == -1)
break;
do
{
b2 = base64DecodeChars[data[i++]];
} while (i < len && b2 == -1);
if (b2 == -1)
break;
sb.append((char) ((b1 << 2) | ((b2 & 0x30) >>> 4)));
do
{
b3 = data[i++];
if (b3 == 61)
return sb.toString().getBytes("iso8859-1");
b3 = base64DecodeChars[b3];
} while (i < len && b3 == -1);
if (b3 == -1)
break;
sb.append((char) (((b2 & 0x0f) << 4) | ((b3 & 0x3c) >>> 2)));
do
{
b4 = data[i++];
if (b4 == 61)
return sb.toString().getBytes("iso8859-1");
b4 = base64DecodeChars[b4];
} while (i < len && b4 == -1);
if (b4 == -1)
break;
sb.append((char) (((b3 & 0x03) << 6) | b4));
}
return sb.toString().getBytes("iso8859-1");
}
}
最后附上工程代码，此处传送门：点击打开链接
工程界面如下：
