基于AES和MAC的Java加密
我正试图找到一种方法来完成我的Java课程。我被要求加密一个文件,但老实说,我没有真正理解说明。我实现了文件加密和解密,但我怀疑它是否符合说明中的要求。说明如下:基于AES和MAC的Java加密,java,encryption,cryptography,aes,hmac,Java,Encryption,Cryptography,Aes,Hmac,我正试图找到一种方法来完成我的Java课程。我被要求加密一个文件,但老实说,我没有真正理解说明。我实现了文件加密和解密,但我怀疑它是否符合说明中的要求。说明如下: 加密分为三个阶段: 生成16字节随机数据作为CBC模式所需的初始向量(IV) 使用PKCS5填充方案,在CBC模式下应用AES密码加密文件内容 应用MAC密码(例如,“HmacSHA1”)来计算封装IV和密文的MAC 加密文件将是以下数据的串联:16字节IV | | |密文| | 20字节HMAC 我写的代码是这样的,它成功地加密
- 加密分为三个阶段:
- 生成16字节随机数据作为CBC模式所需的初始向量(IV)
- 使用PKCS5填充方案,在CBC模式下应用AES密码加密文件内容
- 应用MAC密码(例如,“HmacSHA1”)来计算封装IV和密文的MAC
- 加密文件将是以下数据的串联:16字节IV | | |密文| | 20字节HMAC
import java.io.FileNotFoundException;
import java.io.*;
import java.util.Scanner;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.security.AlgorithmParameters;
import java.security.SecureRandom;
import java.security.spec.KeySpec;
import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.SecretKeySpec;
public class AESFileEncryption {
/*public AESFileEncryption(String nameoffile){
}
public String FileReturn(String filename){
String fl = filename;
return fl;
}*/
public static void main(String[] args) throws Exception {
File f = new File("plainfile.txt");
File g = new File("plainfile.txt.8102");
File fl = new File("plainfile.txt.8102");
if(g.exists() && !g.isDirectory()){
System.out.println("The file is already encrypted...");
String fname = fl.getAbsolutePath();
System.out.print("Absolute Encrypted File Pathname => "+ fname);
System.exit(0);
}
else if(f.exists() && !f.isDirectory()) {
System.out.println(" The file is found.The encryption process is going to begin...");
}
else{
System.out.println(" The file is missing!!!!");
System.exit(0);
}
// file to be encrypted
FileInputStream inFile = new FileInputStream("plainfile.txt");
// encrypted file
FileOutputStream outFile = new FileOutputStream("plainfile.txt.8102");
// password to encrypt the file
Scanner scan= new Scanner(System.in);
System.out.println("Enter the password : => ");
String password= scan.nextLine();
//String password = "javapapers";
// password, iv and salt should be transferred to the other end
// in a secure manner
// salt is used for encoding
// writing it to a file
// salt should be transferred to the recipient securely
// for decryption
byte[] salt = new byte[8];
SecureRandom secureRandom = new SecureRandom();
secureRandom.nextBytes(salt);
FileOutputStream saltOutFile = new FileOutputStream("salt.enc");
saltOutFile.write(salt);
saltOutFile.close();
SecretKeyFactory factory = SecretKeyFactory
.getInstance("PBKDF2WithHmacSHA1");
KeySpec keySpec = new PBEKeySpec(password.toCharArray(), salt, 65536,
256);
SecretKey secretKey = factory.generateSecret(keySpec);
SecretKey secret = new SecretKeySpec(secretKey.getEncoded(), "AES");
//
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE, secret);
AlgorithmParameters params = cipher.getParameters();
// iv adds randomness to the text and just makes the mechanism more
// secure
// used while initializing the cipher
// file to store the iv
FileOutputStream ivOutFile = new FileOutputStream("iv.enc");
byte[] iv = params.getParameterSpec(IvParameterSpec.class).getIV();
ivOutFile.write(iv);
ivOutFile.close();
//file encryption
byte[] input = new byte[64];
int bytesRead;
while ((bytesRead = inFile.read(input)) != -1) {
byte[] output = cipher.update(input, 0, bytesRead);
if (output != null)
outFile.write(output);
}
byte[] output = cipher.doFinal();
if (output != null)
outFile.write(output);
inFile.close();
outFile.flush();
outFile.close();
System.out.println("File Encrypted.");
}
}
讲师的意思是应该应用HMAC为密文创建身份验证标签。这就是所谓的。HMAC是一个密钥哈希函数,它为拥有正确密钥的收件人提供完整性/真实性检查。因为它本质上是一个散列函数,所以它通过更新内部状态来工作
Mac mac = Mac.getInstance("HmacSHA1");
SecretKeySpec macKey = new SecretKeySpec(macKeyBytes, "HmacSHA1");
mac.init(macKey);
mac.update(iv); // update for IV
...
mac.update(output); // update for each ciphertext chunk
...
byte[] authTag = mac.doFinal();
outfile.write(authTag); // at the very end
一个问题仍然存在,那就是macKeyBytes
的生成。它不应与通过PBKDF2从密码生成的加密密钥相同。您应该使用生成的密钥分别派生加密和MAC密钥。这通常是用来完成的,但是您也可以再次使用HMAC来完成。伪代码:
byte[] encKeyBytes = hmacSha256(key, "Encryption");
byte[] macKeyBytes = hmacSha256(key, "Authentication");
该指令没有说明任何关于密钥或密码的内容,因此我假设它应该是一个静态密钥(用于测试目的)。但是您使用PBKDF2的方式是可以的,但是salt也必须写入文件。否则,如果没有随机salt,收件人将无法派生相同的密钥。此外,salt的长度应该大约为16字节
当前代码的另一个问题是,您正在将IV写入一个单独的文件。不要那样做。只需将IV写入密文文件的开头。IV的大小与CBC模式下的块相同,AES的固定块大小为16字节。接收者总是知道要为IV读取多少字节