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。

  1 package pack1;
  2
  3 import java.security.Key;
  4 import java.security.KeyFactory;
  5 import java.security.KeyPair;
  6 import java.security.KeyPairGenerator;
  7 import java.security.PrivateKey;
  8 import java.security.PublicKey;
  9 import java.security.Signature;
 10 import java.security.interfaces.RSAPrivateKey;
 11 import java.security.interfaces.RSAPublicKey;
 12 import java.security.spec.PKCS8EncodedKeySpec;
 13 import java.security.spec.X509EncodedKeySpec;
 14
 15 import javax.crypto.Cipher;
 16
 17 import org.apache.commons.codec.binary.Base64;
 18
 19 import sun.misc.BASE64Decoder;
 20 import sun.misc.BASE64Encoder;
 21
 22
 23 public class RSAtest{
 24     public static final String KEY_ALGORITHM="RSA";
 25     public static final String SIGNATURE_ALGORITHM="MD5withRSA";
 26     private static final int KEY_SIZE=1024;
 27     private static final String PUBLIC_KEY="RSAPublicKey";
 28     private static final String PRIVATE_KEY="RSAPrivateKey";
 29     public static String str_pubK = "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCqPvovSfXcwBbW8cKMCgwqNpsYuzF8RPAPFb7LGsnVo44JhM/xxzDyzoYtdfNmtbIuKVi9PzIsyp6rg+09gbuI6UGwBZ5DWBDBMqv5MPdOF5dCQkB2Bbr5yPfURPENypUz+pBFBg41d+BC+rwRiXELwKy7Y9caD/MtJyHydj8OUwIDAQAB";
 30     public static String str_priK = "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";
 31       /**
 32        * 使用getPublicKey得到公钥,返回类型为PublicKey
 33        * @param key 密钥字符串（经过base64编码）
 34        * @throws Exception
 35        */
 36       public static PublicKey getPublicKey(String key) throws Exception {
 37             byte[] keyBytes;
 38             keyBytes = (new BASE64Decoder()).decodeBuffer(key);
 39             X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);
 40             KeyFactory keyFactory = KeyFactory.getInstance("RSA");
 41             PublicKey publicKey = keyFactory.generatePublic(keySpec);
 42             return publicKey;
 43       }
 44       /**
 45        * 得到私钥
 46        * @param key 密钥字符串（经过base64编码）
 47        * @throws Exception
 48        */
 49       public static PrivateKey getPrivateKey(String key) throws Exception {
 50             byte[] keyBytes;
 51             keyBytes = (new BASE64Decoder()).decodeBuffer(key);
 52             PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(keyBytes);
 53             KeyFactory keyFactory = KeyFactory.getInstance("RSA");
 54             PrivateKey privateKey = keyFactory.generatePrivate(keySpec);
 55             return privateKey;
 56       }
 57
 58       //***************************签名和验证*******************************
 59       public static byte[] sign(byte[] data) throws Exception{
 60         PrivateKey priK = getPrivateKey(str_priK);
 61           Signature sig = Signature.getInstance(SIGNATURE_ALGORITHM);
 62           sig.initSign(priK);
 63           sig.update(data);
 64           return sig.sign();
 65       }
 66
 67       public static boolean verify(byte[] data,byte[] sign) throws Exception{
 68           PublicKey pubK = getPublicKey(str_pubK);
 69           Signature sig = Signature.getInstance(SIGNATURE_ALGORITHM);
 70           sig.initVerify(pubK);
 71           sig.update(data);
 72           return sig.verify(sign);
 73       }
 74
 75       //************************加密解密**************************
 76       public static byte[] encrypt(byte[] bt_plaintext)throws Exception{
 77           PublicKey publicKey = getPublicKey(str_pubK);
 78           Cipher cipher = Cipher.getInstance("RSA");
 79           cipher.init(Cipher.ENCRYPT_MODE, publicKey);
 80         byte[] bt_encrypted = cipher.doFinal(bt_plaintext);
 81         return bt_encrypted;
 82       }
 83
 84       public static byte[] decrypt(byte[] bt_encrypted)throws Exception{
 85         PrivateKey privateKey = getPrivateKey(str_priK);
 86         Cipher cipher = Cipher.getInstance("RSA");
 87         cipher.init(Cipher.DECRYPT_MODE, privateKey);
 88         byte[] bt_original = cipher.doFinal(bt_encrypted);
 89         return bt_original;
 90       }
 91       //********************main函数：加密解密和签名验证*********************
 92       public static void main(String[] args) throws Exception {
 93             String str_plaintext = "这是一段用来测试密钥转换的明文";
 94             System.err.println("明文："+str_plaintext);
 95             byte[] bt_cipher = encrypt(str_plaintext.getBytes());
 96             System.out.println("加密后："+Base64.encodeBase64String(bt_cipher));
 97
 98             byte[] bt_original = decrypt(bt_cipher);
 99             String str_original = new String(bt_original);
100             System.out.println("解密结果:"+str_original);
101
102             String str="被签名的内容";
103             System.err.println("\n原文:"+str);
104             byte[] signature=sign(str.getBytes());
105             System.out.println("产生签名："+Base64.encodeBase64String(signature));
106             boolean status=verify(str.getBytes(), signature);
107             System.out.println("验证情况："+status);
108       }
109
110 }

曾经在百度知道上寻求过这个问题，一直都没能很好的解决。今日coding测试成功，来分享一下，技术有限，不足之处望指正。