RSA解密时BadPaddingException
public class RSATest2 {
public static void main(String[] args) {
try {
RSATest2 encrypt = new RSATest2();
KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA");
keyPairGen.initialize(1024);
KeyPair keyPair = keyPairGen.generateKeyPair();
// 私钥，其实私钥是指定好的，与公钥是一对，我这里随便取一个暂时用用。
RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
// 公钥不用，只用上面的私钥
RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
// 假设这是加密后的字符串，我要把它解密
String encryptedStr = "sdfds23fd23";
/*
* 为什么会出现javax.crypto.BadPaddingException: Data must start with zero
* 看了Cipher的文档也不懂是什么意思，“如果此 cipher
* 为解密模式，并且未请求填充或不填充，但解密的数据没有用适当的填充字节所限制” 需要怎么做？
*/
byte[] de = encrypt.decrypt(privateKey, encryptedStr.getBytes());
System.out.println(de.toString());
} catch (Exception e) {
e.printStackTrace();
}
}
protected byte[] decrypt(RSAPrivateKey privateKey, byte[] obj) {
if (privateKey != null) {
try {
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.DECRYPT_MODE, privateKey);
return cipher.doFinal(obj);
} catch (Exception e) {
e.printStackTrace();
}
}
return null;
}
}
先说说正确的情况，先用Cipher.getInstance("RSA");初始化为加密模式，把一个指定的串加密后返回一个byte数组；如果把这个byte数组传给解密的doFinal方法，解密成功。
但是传给解密doFinal方法的参数是普通的一个字符串产生的byte数组，那么就会抛出
javax.crypto.BadPaddingException: Data must start with zero
at sun.security.rsa.RSAPadding.unpadV15(Unknown Source)
at sun.security.rsa.RSAPadding.unpad(Unknown Source)
at com.sun.crypto.provider.RSACipher.a(DashoA6275)
at com.sun.crypto.provider.RSACipher.engineDoFinal(DashoA6275)
at javax.crypto.Cipher.doFinal(DashoA12275)
at RSATest2.decrypt(RSATest2.java:41)
at RSATest2.main(RSATest2.java:29)
java.lang.NullPointerException
at RSATest2.main(RSATest2.java:30)
为什么呢？
在文档中找到了如下描述，可是可以帮我理解一下么，谢谢。
BadPaddingException - 如果此 cipher 为解密模式，并且未请求填充或不填充，但解密的数据没有用适当的填充字节所限制
[解决办法]
没用过，友情帮你顶
[解决办法]
那个当然，你的给普通字符串的byte数组都不符合加密后的排列要求，当然会出错。
[解决办法]
帮顶
[解决办法]
终于搞定了，基本功太差，得好好补补了。
加密后产生的byte数组转成string时要在各byte之间加个标识符，我加了个空格，
然后再根据空格分隔转换回byte数组。如果不加标识符，由于byte值可能是一位到三位，无法知道某一个byte是在哪里结束。当然也可以在转成string时补0。或者转成16进制固定为两位长。
code:
public class RSATest {
public static void main(String[] args) {
try {
RSATest encrypt = new RSATest();
KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA");
keyPairGen.initialize(1024);
KeyPair keyPair = keyPairGen.generateKeyPair();
RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
String str = "Hello World!";
System.out.println("String will be encrypted: " + str);
byte[] e = encrypt.encrypt(publicKey, str.getBytes());
String tmp1 = encrypt.bytesToString(e);
System.out
.println("encrypted String's bytes, use
bytesToString() method convert bytes to string: " + tmp1);
String[] strArr = tmp1.split(" ");
int len = strArr.length;
byte[] clone = new byte[len];
for (int i = 0; i < len; i++) {
clone[i] = Byte.parseByte(strArr[i]);
}
System.out.println("convert to String, then back to bytes
again: " + encrypt.bytesToString(clone));
byte[] d = encrypt.decrypt(privateKey, clone);
System.out.println("decrypted String's bytes, use
bytesToString() method convert bytes to string:"
+ encrypt.bytesToString(d));
System.out.println("construct a string by decrypted
string's bytes: " + new String(d));
} catch (Exception e) {
e.printStackTrace();
}
}
protected String bytesToString(byte[] encrytpByte) {
String result = "";
for (Byte bytes : encrytpByte) {
result += bytes.toString() + " ";
}
return result;
}
protected byte[] encrypt(RSAPublicKey publicKey, byte[] obj) {
if (publicKey != null) {
try {
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
return cipher.doFinal(obj);
} catch (Exception e) {
e.printStackTrace();
}
}
return null;
}
protected byte[] decrypt(RSAPrivateKey privateKey, byte[] obj) {
if (privateKey != null) {
try {
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.DECRYPT_MODE, privateKey);
return cipher.doFinal(obj);
} catch (Exception e) {
e.printStackTrace();
}
}
return null;
}
}
运行结果：
String will be encrypted: Hello World!
encrypted String's bytes, use bytesToString() method convert bytes to
string: 79 62 -105 -47 -61 45 64 -11 -8 -120 30 31 37 -111 49 -30 88
-12 93 -77 3 39 -13 -18 68 -104 0 30 85 26 104 15 -126 -39 12 110 -84
68 -43 73 35 121 -20 -69 -84 85 -33 -123 -48 -68 -85 -106 41 -84 20
-17 87 -81 42 -67 -87 122 -2 37 74 27 103 112 58 -125 -87 -32 96 -56
65 -2 -103 -28 70 107 2 28 87 75 -8 -62 54 12 -7 -108 -123 120 -63 -83
13 -89 -21 58 -51 -84 66 25 103 -114 -14 110 80 58 74 95 -57 -73 -78
-46 56 -83 -72 -38 2 43 25 12 56 12 101 15 91 -37
convert to String, then back to bytes again: 79 62 -105 -47 -61 45 64
-11 -8 -120 30 31 37 -111 49 -30 88 -12 93 -77 3 39 -13 -18 68 -104 0
30 85 26 104 15 -126 -39 12 110 -84 68 -43 73 35 121 -20 -69 -84 85
-33 -123 -48 -68 -85 -106 41 -84 20 -17 87 -81 42 -67 -87 122 -2 37 74
27 103 112 58 -125 -87 -32 96 -56 65 -2 -103 -28 70 107 2 28 87 75 -8
-62 54 12 -7 -108 -123 120 -63 -83 13 -89 -21 58 -51 -84 66 25 103
-114 -14 110 80 58 74 95 -57 -73 -78 -46 56 -83 -72 -38 2 43 25 12 56
12 101 15 91 -37
decrypted String's bytes, use bytesToString() method convert bytes to
string:72 101 108 108 111 32 87 111 114 108 100 33
construct a string by decrypted string's bytes: Hello World!
