RSA密钥的数据类型转换：由合法的string到PublicKey或PrivateKey

给定base64编码的RSA公钥和私钥，下面两段代码可以将string类型转换为PublicKey和PrivateKey类型，后面给出完整的测试程序。

转换代码如下：

public static PublicKey getPublicKey(String key) throws Exception {
byte[] keyBytes;
keyBytes = (new BASE64Decoder()).decodeBuffer(key);
X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
PublicKey publicKey = keyFactory.generatePublic(keySpec);
return publicKey;
}

public static PrivateKey getPrivateKey(String key) throws Exception {
byte[] keyBytes;
keyBytes = (new BASE64Decoder()).decodeBuffer(key);
PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(keyBytes);
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
PrivateKey privateKey = keyFactory.generatePrivate(keySpec);
return privateKey;
}

注意：不是随便敲一串字母就可以作为密钥string使用的，需要用严格的代码生成公钥串和私钥串。

完整的程序如下：

程序中包含密钥转换、加密和签名三个部分。

<pre name="code" class="java">package pack1;

import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.Signature;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;

import javax.crypto.Cipher;

import org.apache.commons.codec.binary.Base64;

import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;

public class RSAtest{
public static final String KEY_ALGORITHM="RSA";
public static final String SIGNATURE_ALGORITHM="MD5withRSA";
private static final int KEY_SIZE=1024;
private static final String PUBLIC_KEY="RSAPublicKey";
private static final String PRIVATE_KEY="RSAPrivateKey";
public static String str_pubK = "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCqPvovSfXcwBbW8cKMCgwqNpsYuzF8RPAPFb7LGsnVo44JhM/xxzDyzoYtdfNmtbIuKVi9PzIsyp6rg+09gbuI6UGwBZ5DWBDBMqv5MPdOF5dCQkB2Bbr5yPfURPENypUz+pBFBg41d+BC+rwRiXELwKy7Y9caD/MtJyHydj8OUwIDAQAB";
public static String str_priK = "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";
/**
* 得到公钥
* @param key 密钥字符串（经过base64编码）
* @throws Exception
*/
public static PublicKey getPublicKey(String key) throws Exception {
byte[] keyBytes;
keyBytes = (new BASE64Decoder()).decodeBuffer(key);
X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
PublicKey publicKey = keyFactory.generatePublic(keySpec);
return publicKey;
}
/**
* 得到私钥
* @param key 密钥字符串（经过base64编码）
* @throws Exception
*/
public static PrivateKey getPrivateKey(String key) throws Exception {
byte[] keyBytes;
keyBytes = (new BASE64Decoder()).decodeBuffer(key);
PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(keyBytes);
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
PrivateKey privateKey = keyFactory.generatePrivate(keySpec);
return privateKey;
}

//***************************签名和验证*******************************
public static byte[] sign(byte[] data) throws Exception{
PrivateKey priK = getPrivateKey(str_priK);
Signature sig = Signature.getInstance(SIGNATURE_ALGORITHM);
sig.initSign(priK);
sig.update(data);
return sig.sign();
}

public static boolean verify(byte[] data,byte[] sign) throws Exception{
PublicKey pubK = getPublicKey(str_pubK);
Signature sig = Signature.getInstance(SIGNATURE_ALGORITHM);
sig.initVerify(pubK);
sig.update(data);
return sig.verify(sign);
}

//************************加密解密**************************
public static byte[] encrypt(byte[] bt_plaintext)throws Exception{
PublicKey publicKey = getPublicKey(str_pubK);
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
byte[] bt_encrypted = cipher.doFinal(bt_plaintext);
return bt_encrypted;
}

public static byte[] decrypt(byte[] bt_encrypted)throws Exception{
PrivateKey privateKey = getPrivateKey(str_priK);
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.DECRYPT_MODE, privateKey);
byte[] bt_original = cipher.doFinal(bt_encrypted);
return bt_original;
}
//********************main函数：加密解密和签名验证*********************
public static void main(String[] args) throws Exception {
String str_plaintext = "这是一段用来测试密钥转换的明文";
System.err.println("明文："+str_plaintext);
byte[] bt_cipher = encrypt(str_plaintext.getBytes());
System.out.println("加密后："+Base64.encodeBase64String(bt_cipher));

byte[] bt_original = decrypt(bt_cipher);
String str_original = new String(bt_original);
System.out.println("解密结果:"+str_original);

String str="被签名的内容";
System.err.println("\n原文:"+str);
byte[] signature=sign(str.getBytes());
System.out.println("产生签名："+Base64.encodeBase64String(signature));
boolean status=verify(str.getBytes(), signature);
System.out.println("验证情况："+status);
}

}