我正在写一些生成加密日志文件的记录器.不幸的是,密码术不是我的强项.现在我可以写入文件,然后关闭文件.然后我可以打开它,附加一些消息,再次关闭,解密后,我看到文件中间的填充字节.有没有办法使用加密文件,而不必每次我要附加一些消息解密？
编辑：更多的细节.当前实现使用CipherOutputStream.据我所知,没有办法寻求使用它.
如果我将控制输出数据大小可以被块大小整除,我可以使用’NoPadding’选项吗？
解决方法
如果您在
CBC mode中使用AES,则可以使用第二个最后一个块作为IV解密最后一个块,这可能只是部分已满,然后再加密最后一个块的明文,然后是新的明文.
这是一个概念证明：
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.RandomAccessFile;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
public class AppendAES {
public static void appendAES(File file,byte[] data,byte[] key) throws IOException,NoSuchAlgorithmException,NoSuchPaddingException,InvalidKeyException,InvalidAlgorithmParameterException,IllegalBlockSizeException,BadPaddingException {
RandomAccessFile rfile = new RandomAccessFile(file,"rw");
byte[] iv = new byte[16];
byte[] lastBlock = null;
if (rfile.length() % 16L != 0L) {
throw new IllegalArgumentException("Invalid file length (not a multiple of block size)");
} else if (rfile.length() == 16) {
throw new IllegalArgumentException("Invalid file length (need 2 blocks for iv and data)");
} else if (rfile.length() == 0L) {
// new file: start by appending an IV
new SecureRandom().nextBytes(iv);
rfile.write(iv);
// we have our iv,and there's no prior data to reencrypt
} else {
// file length is at least 2 blocks
rfile.seek(rfile.length()-32); // second to last block
rfile.read(iv); // get iv
byte[] lastBlockEnc = new byte[16];
// last block
// it's padded,so we'll decrypt it and
// save it for the beginning of our data
rfile.read(lastBlockEnc);
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.DECRYPT_MODE,new SecretKeySpec(key,"AES"),new IvParameterSpec(iv));
lastBlock = cipher.doFinal(lastBlockEnc);
rfile.seek(rfile.length()-16);
// position ourselves to overwrite the last block
}
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE,new IvParameterSpec(iv));
byte[] out;
if (lastBlock != null) { // lastBlock is null if we're starting a new file
out = cipher.update(lastBlock);
if (out != null) rfile.write(out);
}
out = cipher.doFinal(data);
rfile.write(out);
rfile.close();
}
public static void decryptAES(File file,OutputStream out,BadPaddingException {
// nothing special here,decrypt as usual
FileInputStream fin = new FileInputStream(file);
byte[] iv = new byte[16];
if (fin.read(iv) < 16) {
throw new IllegalArgumentException("Invalid file length (needs a full block for iv)");
};
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.DECRYPT_MODE,new IvParameterSpec(iv));
byte[] buff = new byte[1<<13]; //8kiB
while (true) {
int count = fin.read(buff);
if (count == buff.length) {
out.write(cipher.update(buff));
} else {
out.write(cipher.doFinal(buff,count));
break;
}
}
fin.close();
}
public static void main(String[] args) throws Exception {
byte[] key = new byte[]{0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
for (int i = 0; i<1000; i++) {
appendAES(new File("log.aes"),"All work and no play makes Jack a dull boy. ".getBytes("UTF-8"),key);
}
decryptAES(new File("log.aes"),new FileOutputStream("plain.txt"),key);
}
}
我想指出,输出与通过一次运行中加密所产生的输出没有什么不同.这不是加密的自定义形式 – 它是AES / CBC / PKCS5Padding的标准.唯一的实现具体细节是,在空白文件的情况下,我在开始数据之前写了iv.
编辑：使用CipherOutputStream改进(对我的口味)解决方案：
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.RandomAccessFile;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.CipherInputStream;
import javax.crypto.CipherOutputStream;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
public class AppendAES {
public static CipherOutputStream appendAES(File file,SecretKeySpec key) throws IOException,BadPaddingException {
return appendAES(file,key,null);
}
public static CipherOutputStream appendAES(File file,SecretKeySpec key,SecureRandom sr) throws IOException,"rw");
byte[] iv = new byte[16];
byte[] lastBlock = null;
if (rfile.length() % 16L != 0L) {
throw new IllegalArgumentException("Invalid file length (not a multiple of block size)");
} else if (rfile.length() == 16) {
throw new IllegalArgumentException("Invalid file length (need 2 blocks for iv and data)");
} else if (rfile.length() == 0L) {
// new file: start by appending an IV
if (sr == null) sr = new SecureRandom();
sr.nextBytes(iv);
rfile.write(iv);
} else {
// file length is at least 2 blocks
rfile.seek(rfile.length()-32);
rfile.read(iv);
byte[] lastBlockEnc = new byte[16];
rfile.read(lastBlockEnc);
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.DECRYPT_MODE,new IvParameterSpec(iv));
lastBlock = cipher.doFinal(lastBlockEnc);
rfile.seek(rfile.length()-16);
}
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE,new IvParameterSpec(iv));
byte[] out;
if (lastBlock != null) {
out = cipher.update(lastBlock);
if (out != null) rfile.write(out);
}
CipherOutputStream cos = new CipherOutputStream(new FileOutputStream(rfile.getFD()),cipher);
return cos;
}
public static CipherInputStream decryptAES(File file,BadPaddingException {
FileInputStream fin = new FileInputStream(file);
byte[] iv = new byte[16];
if (fin.read(iv) < 16) {
throw new IllegalArgumentException("Invalid file length (needs a full block for iv)");
};
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.DECRYPT_MODE,new IvParameterSpec(iv));
CipherInputStream cis = new CipherInputStream(fin,cipher);
return cis;
}
public static void main(String[] args) throws Exception {
byte[] keyBytes = new byte[]{
0,15
};
SecretKeySpec key = new SecretKeySpec(keyBytes,"AES");
for (int i = 0; i<100; i++) {
CipherOutputStream cos = appendAES(new File("log.aes"),key);
cos.write("All work and no play ".getBytes("UTF-8"));
cos.write("makes Jack a dull boy. \n".getBytes("UTF-8"));
cos.close();
}
CipherInputStream cis = decryptAES(new File("log.aes"),key);
BufferedReader bread = new BufferedReader(new InputStreamReader(cis,"UTF-8"));
System.out.println(bread.readLine());
cis.close();
}
}
