【发布时间】：2012-12-02 20:32:06
【问题描述】：
我正在尝试使用 Java 中的密码将一个文件的内容加密到另一个文件中。该文件被读取到一个字节数组，加密到另一个字节数组，然后写入新文件。不幸的是，当我尝试反转加密时，输出文件被解密为垃圾。
我强烈怀疑这个问题与每次使用相同的密码时生成相同的密钥有关。我编写了一种测试方法，只要生成密钥就将密钥转储到文件中。密钥以直接和编码形式记录。前者每次都是相同的，但后者总是由于某种原因不同。
老实说，我对加密方法知之甚少，尤其是在 Java 中。我只需要适度安全的数据，并且加密不必承受来自任何拥有大量时间和技能的人的攻击。提前感谢任何对此提出建议的人。
编辑：Esailija 非常友好地指出我总是使用 ENCRYPT_MODE 设置密码。我使用布尔参数更正了问题，但现在出现以下异常：
javax.crypto.IllegalBlockSizeException：使用填充密码解密时，输入长度必须是 8 的倍数
在我看来，密码短语使用不当。我的印象是“PBEWithMD5AndDES”会将它散列成一个 16 字节的代码，这肯定是 8 的倍数。我想知道为什么密钥生成并被很好地用于加密模式，但是在尝试时它会抱怨在完全相同的条件下解密。
import java.various.stuff;
/**Utility class to encrypt and decrypt files**/
public class FileEncryptor {
//Arbitrarily selected 8-byte salt sequence:
private static final byte[] salt = {
(byte) 0x43, (byte) 0x76, (byte) 0x95, (byte) 0xc7,
(byte) 0x5b, (byte) 0xd7, (byte) 0x45, (byte) 0x17
};
private static Cipher makeCipher(String pass, Boolean decryptMode) throws GeneralSecurityException{
//Use a KeyFactory to derive the corresponding key from the passphrase:
PBEKeySpec keySpec = new PBEKeySpec(pass.toCharArray());
SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("PBEWithMD5AndDES");
SecretKey key = keyFactory.generateSecret(keySpec);
//Create parameters from the salt and an arbitrary number of iterations:
PBEParameterSpec pbeParamSpec = new PBEParameterSpec(salt, 42);
/*Dump the key to a file for testing: */
FileEncryptor.keyToFile(key);
//Set up the cipher:
Cipher cipher = Cipher.getInstance("PBEWithMD5AndDES");
//Set the cipher mode to decryption or encryption:
if(decryptMode){
cipher.init(Cipher.ENCRYPT_MODE, key, pbeParamSpec);
} else {
cipher.init(Cipher.DECRYPT_MODE, key, pbeParamSpec);
}
return cipher;
}
/**Encrypts one file to a second file using a key derived from a passphrase:**/
public static void encryptFile(String fileName, String pass)
throws IOException, GeneralSecurityException{
byte[] decData;
byte[] encData;
File inFile = new File(fileName);
//Generate the cipher using pass:
Cipher cipher = FileEncryptor.makeCipher(pass, false);
//Read in the file:
FileInputStream inStream = new FileInputStream(inFile);
decData = new byte[(int)inFile.length()];
inStream.read(decData);
inStream.close();
//Encrypt the file data:
encData = cipher.doFinal(decData);
//Write the encrypted data to a new file:
FileOutputStream outStream = new FileOutputStream(new File(fileName + ".encrypted"));
outStream.write(encData);
outStream.close();
}
/**Decrypts one file to a second file using a key derived from a passphrase:**/
public static void decryptFile(String fileName, String pass)
throws GeneralSecurityException, IOException{
byte[] encData;
byte[] decData;
File inFile = new File(fileName);
//Generate the cipher using pass:
Cipher cipher = FileEncryptor.makeCipher(pass, true);
//Read in the file:
FileInputStream inStream = new FileInputStream(inFile);
encData = new byte[(int)inFile.length()];
inStream.read(encData);
inStream.close();
//Decrypt the file data:
decData = cipher.doFinal(encData);
//Write the decrypted data to a new file:
FileOutputStream target = new FileOutputStream(new File(fileName + ".decrypted.txt"));
target.write(decData);
target.close();
}
/**Record the key to a text file for testing:**/
private static void keyToFile(SecretKey key){
try {
File keyFile = new File("C:\\keyfile.txt");
FileWriter keyStream = new FileWriter(keyFile);
String encodedKey = "\n" + "Encoded version of key: " + key.getEncoded().toString();
keyStream.write(key.toString());
keyStream.write(encodedKey);
keyStream.close();
} catch (IOException e) {
System.err.println("Failure writing key to file");
e.printStackTrace();
}
}
}
【问题讨论】：
标签： java encryption