我正在尝试编写一个应用程序，用户应该可以从算法操作模式中选择（CBC，CTR ...）
我正在使用这段代码（不是我写的）用于AES加密，但我注意到我只能在NoPadding上使用它，我不明白为什么。
public void setPassword(String password) throws UnsupportedEncodingException {
this.password = password.getBytes("UTF-16LE");
debug("Using password: ", this.password);
}
public void encrypt(int version, String fromPath, String toPath) throws IOException, GeneralSecurityException {
InputStream in = null;
OutputStream out = null;
try {
in = new BufferedInputStream(new FileInputStream(fromPath));
debug("Opened for reading: " + fromPath);
out = new BufferedOutputStream(new FileOutputStream(toPath));
debug("Opened for writing: " + toPath);
encrypt(version, in, out);
} finally {
if (in != null) {
in.close();
}
if (out != null) {
out.close();
}
}
}
public void encrypt(int version, InputStream in, OutputStream out) throws IOException, GeneralSecurityException {
try {
byte[] text = null;
ivSpec1 = new IvParameterSpec(generateIv1());
aesKey1 = new SecretKeySpec(generateAESKey1(ivSpec1.getIV(), password), CRYPT_ALG);
ivSpec2 = new IvParameterSpec(generateIV2());
aesKey2 = new SecretKeySpec(generateAESKey2(), CRYPT_ALG);
debug("IV1: ", ivSpec1.getIV());
debug("AES1: ", aesKey1.getEncoded());
debug("IV2: ", ivSpec2.getIV());
debug("AES2: ", aesKey2.getEncoded());
out.write("AES".getBytes("UTF-8")); // Heading.
out.write(version); // Version.
out.write(0); // Reserved.
if (version == 2) { // No extensions.
out.write(0);
out.write(0);
}
out.write(ivSpec1.getIV()); // Initialization Vector.
text = new byte[BLOCK_SIZE + KEY_SIZE];
cipher.init(Cipher.ENCRYPT_MODE, aesKey1, ivSpec1);
cipher.update(ivSpec2.getIV(), 0, BLOCK_SIZE, text);
cipher.doFinal(aesKey2.getEncoded(), 0, KEY_SIZE, text, BLOCK_SIZE);
out.write(text); // Crypted IV and key.
debug("IV2 + AES2 ciphertext: ", text);
hmac.init(new SecretKeySpec(aesKey1.getEncoded(), HMAC_ALG));
text = hmac.doFinal(text);
out.write(text); // HMAC from previous cyphertext.
debug("HMAC1: ", text);
cipher.init(Cipher.ENCRYPT_MODE, aesKey2, ivSpec2);
hmac.init(new SecretKeySpec(aesKey2.getEncoded(), HMAC_ALG));
text = new byte[BLOCK_SIZE];
int len, last = 0;
while ((len = in.read(text)) > 0) {
cipher.update(text, 0, BLOCK_SIZE, text);
hmac.update(text);
out.write(text); // Crypted file data block.
last = len;
}
last &= 0x0f;
out.write(last); // Last block size mod 16.
debug("Last block size mod 16: " + last);
text = hmac.doFinal();
out.write(text); // HMAC from previous cyphertext.
debug("HMAC2: ", text);
} catch (InvalidKeyException e) {
throw new GeneralSecurityException(JCE_EXCEPTION_MESSAGE, e);
}
}
public void decrypt(String fromPath, String toPath) throws IOException, GeneralSecurityException {
InputStream in = null;
OutputStream out = null;
try {
in = new BufferedInputStream(new FileInputStream(fromPath));
debug("Opened for reading: " + fromPath);
out = new BufferedOutputStream(new FileOutputStream(toPath));
debug("Opened for writing: " + toPath);
decrypt(new File(fromPath).length(), in, out);
} finally {
if (in != null) {
in.close();
}
if (out != null) {
out.close();
}
}
}
public void decrypt(long inSize, InputStream in, OutputStream out) throws IOException, GeneralSecurityException {
try {
byte[] text = null, backup = null;
long total = 3 + 1 + 1 + BLOCK_SIZE + BLOCK_SIZE + KEY_SIZE + SHA_SIZE + 1 + SHA_SIZE;
int version;
text = new byte[3];
readBytes(in, text); // Heading.
if (!new String(text, "UTF-8").equals("AES")) {
throw new IOException("Invalid file header");
}
version = in.read(); // Version.
if (version < 1 || version > 2) {
throw new IOException("Unsupported version number: " + version);
}
debug("Version: " + version);
in.read(); // Reserved.
if (version == 2) { // Extensions.
text = new byte[2];
int len;
do {
readBytes(in, text);
len = ((0xff & (int) text[0]) << 8) | (0xff & (int) text[1]);
if (in.skip(len) != len) {
throw new IOException("Unexpected end of extension");
}
total += 2 + len;
debug("Skipped extension sized: " + len);
} while (len != 0);
}
text = new byte[BLOCK_SIZE];
readBytes(in, text); // Initialization Vector.
ivSpec1 = new IvParameterSpec(text);
aesKey1 = new SecretKeySpec(generateAESKey1(ivSpec1.getIV(), password), CRYPT_ALG);
debug("IV1: ", ivSpec1.getIV());
debug("AES1: ", aesKey1.getEncoded());
cipher.init(Cipher.DECRYPT_MODE, aesKey1, ivSpec1);
backup = new byte[BLOCK_SIZE + KEY_SIZE];
readBytes(in, backup); // IV and key to decrypt file contents.
debug("IV2 + AES2 ciphertext: ", backup);
text = cipher.doFinal(backup);
ivSpec2 = new IvParameterSpec(text, 0, BLOCK_SIZE);
aesKey2 = new SecretKeySpec(text, BLOCK_SIZE, KEY_SIZE, CRYPT_ALG);
debug("IV2: ", ivSpec2.getIV());
debug("AES2: ", aesKey2.getEncoded());
hmac.init(new SecretKeySpec(aesKey1.getEncoded(), HMAC_ALG));
backup = hmac.doFinal(backup);
text = new byte[SHA_SIZE];
readBytes(in, text); // HMAC and authenticity test.
if (!Arrays.equals(backup, text)) {
throw new IOException("Message has been altered or password incorrect");
}
debug("HMAC1: ", text);
total = inSize - total; // Payload size.
if (total % BLOCK_SIZE != 0) {
throw new IOException("Input file is corrupt");
}
if (total == 0) { // Hack: empty files won't enter block-processing
// for-loop below.
in.read(); // Skip last block size mod 16.
}
debug("Payload size: " + total);
cipher.init(Cipher.DECRYPT_MODE, aesKey2, ivSpec2);
hmac.init(new SecretKeySpec(aesKey2.getEncoded(), HMAC_ALG));
backup = new byte[BLOCK_SIZE];
text = new byte[BLOCK_SIZE];
for (int block = (int) (total / BLOCK_SIZE); block > 0; block--) {
int len = BLOCK_SIZE;
if (in.read(backup, 0, len) != len) { // Cyphertext block.
throw new IOException("Unexpected end of file contents");
}
cipher.update(backup, 0, len, text);
hmac.update(backup, 0, len);
if (block == 1) {
int last = in.read(); // Last block size mod 16.
debug("Last block size mod 16: " + last);
len = (last > 0 ? last : BLOCK_SIZE);
}
out.write(text, 0, len);
}
out.write(cipher.doFinal());
backup = hmac.doFinal();
text = new byte[SHA_SIZE];
readBytes(in, text); // HMAC and authenticity test.
if (!Arrays.equals(backup, text)) {
throw new IOException("Message has been altered or password incorrect");
}
debug("HMAC2: ", text);
} catch (InvalidKeyException e) {
throw new GeneralSecurityException(JCE_EXCEPTION_MESSAGE, e);
}
}
当我尝试使用PCS5Padding加密文件时，出现此错误：
Output buffer too short: 32 bytes given, 48 bytes needed
javax.crypto.ShortBufferException: Output buffer too short: 32 bytes given, 48 bytes needed
答案 0 :(得分：4)
您正在获得该异常，因为正如消息所示，输出缓冲区太短。
我不知道抛出异常的哪一行（你没有发布堆栈跟踪），但似乎代码只处理特定长度的密文，并且在应用填充时失败（作为PKCS＃ 5填充可以添加整个块。）
加密“主”加密密钥有什么意义？它不会增加任何安全性，但会更复杂。按照古老的格言，复杂性是安全的敌人。
还要注意家庭滚动（或复制粘贴的互联网）加密的危险。我可以立即发现至少一个漏洞 - MAC-then-pad序列允许填充oracle攻击。使用经过实践检验的解决方案会更好，例如Keyczar。