如果您在CBC模式下使用AES
，则可以使用倒数第二个块作为IV来解密最后一个块（可能仅部分填充），然后再次加密最后一个块的明文，然后再加密新的明文。
这是概念证明：
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 SecretKeySpec(key,"AES"), 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, byte[] key) throws IOException, NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, InvalidAlgorithmParameterException, IllegalBlockSizeException, 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 SecretKeySpec(key,"AES"), 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,0,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); }}我想指出的是，输出与一次加密所有内容所产生的输出没有什么不同。这 不是 自定义的加密形式，而是标准的AES / CBC /
PKCS5Padding。唯一特定于实现的细节是，对于空白文件，我在开始数据之前已经编写了iv。
编辑：改进了（根据我的口味）使用的解决方案
CipherOutputStream：
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, NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, InvalidAlgorithmParameterException, IllegalBlockSizeException, BadPaddingException { return appendAES(file, key, null); } public static CipherOutputStream appendAES(File file, SecretKeySpec key, SecureRandom sr) 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 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, key, new IvParameterSpec(iv)); lastBlock = cipher.doFinal(lastBlockEnc); rfile.seek(rfile.length()-16); } Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding"); cipher.init(Cipher.ENCRYPT_MODE, key, 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, SecretKeySpec key) throws IOException, NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, InvalidAlgorithmParameterException, IllegalBlockSizeException, 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, key, new IvParameterSpec(iv)); CipherInputStream cis = new CipherInputStream(fin,cipher); return cis; } public static void main(String[] args) throws Exception { byte[] keyBytes = new byte[]{ 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15 }; 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(); }}
