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我一直在玩Java加密，並且遇到了奇怪的行爲。當使用當長度被16整除時，CipherInputStream跳過最後一個字節
InputStream fin = new ByteArrayInputStream(data);
CipherInputStream cin = new CipherInputStream(fin, mEcipher);
加密byte[] data其中mEcipher是公初始化AES密碼，當陣列的長度是16的倍數。然後，加密跳過最後16個字節這工作總是除了。我必須通過添加額外的16個0來解決這個問題，這不能是意圖，因爲加密是按每個16字節塊完成的，因此不需要最後字節爲0.
下面是一個小演示行爲的示例。爲什麼會發生這種情況，我該如何解決？它只是在加密時纔會發生，解密工作正常（並且長度總是16的倍數）。例程encrypt()和decrypt()寫成完全對稱。我認爲這是CipherInputStream中的一個奇怪的怪癖，但我想了解它的細節。
class Crypto {
String mPassword = null;
public final static int SALT_LEN = 8;
byte[] mInitVec = null;
byte[] mSalt = null;
Cipher mEcipher = null;
Cipher mDecipher = null;
private final int KEYLEN_BITS = 128; // see notes below where this is used.
private final int ITERATIONS = 65536;
private final int MAX_FILE_BUF = 1024;
public Crypto(String password) {mPassword = password;}
public byte[] getSalt() {return (mSalt);}
public byte[] getInitVec() {return (mInitVec);}
public void setupEncrypt() throws Exception {
mSalt = new byte[SALT_LEN];
SecureRandom rnd = new SecureRandom();
rnd.nextBytes(mSalt);
SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
KeySpec spec = new PBEKeySpec(mPassword.toCharArray(), mSalt, ITERATIONS, KEYLEN_BITS);
SecretKey tmp = factory.generateSecret(spec);
SecretKey secret = new SecretKeySpec(tmp.getEncoded(), "AES");
mEcipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
mEcipher.init(Cipher.ENCRYPT_MODE, secret);
AlgorithmParameters params = mEcipher.getParameters();
mInitVec = params.getParameterSpec(IvParameterSpec.class).getIV();
}
public void setupDecrypt(String initvec, String salt) throws Exception {
mSalt = decodeHex(salt.toCharArray());
mInitVec = decodeHex(initvec.toCharArray());
SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
KeySpec spec = new PBEKeySpec(mPassword.toCharArray(), mSalt, ITERATIONS, KEYLEN_BITS);
SecretKey tmp = factory.generateSecret(spec);
SecretKey secret = new SecretKeySpec(tmp.getEncoded(), "AES");
mDecipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
mDecipher.init(Cipher.DECRYPT_MODE, secret, new IvParameterSpec(mInitVec));
}
public byte[] decrypt(byte[] data) throws IllegalBlockSizeException, BadPaddingException, IOException {
byte[] decdata = new byte[data.length];
int totalread = 0;
int nread = 0;
byte[] substr = new byte[16];
InputStream fin = new ByteArrayInputStream(data);
CipherInputStream cin = new CipherInputStream(fin, mDecipher);
while ((nread = cin.read(substr)) > 0) {
for (int i = 0; i < nread; i++) decdata[totalread+i] = substr[i];
totalread += nread;
}
fin.close();
return decdata;
}
public byte[] encrypt(byte[] data) throws IllegalBlockSizeException, BadPaddingException, IOException {
System.out.println("data.length="+data.length);
byte[] encdata = new byte[data.length+15-(data.length-1)%16];
System.out.println("encdata.length="+encdata.length);
int totalread = 0;
int nread = 0;
byte[] substr = new byte[16];
InputStream fin = new ByteArrayInputStream(data);
CipherInputStream cin = new CipherInputStream(fin, mEcipher);
while ((nread = cin.read(substr)) > 0 && totalread<data.length) {
for (int i = 0; i < nread; i++) encdata[totalread+i] = substr[i];
totalread += nread;
}
fin.close();
return encdata;
}
public static void main(String[] args) throws Exception {
String inpstr = "Dit is een test.Zit if een mewt.";
Crypto en = new Crypto("mypassword");
en.setupEncrypt();
String iv = encodeHexString(en.getInitVec()).toUpperCase();
String salt = encodeHexString(en.getSalt()).toUpperCase();
byte[] inp = inpstr.getBytes();
byte[] enc = en.encrypt(inp);
System.out.println("In: "+Arrays.toString(inp));
System.out.println("En: "+Arrays.toString(enc));
Crypto dc = new Crypto("mypassword");
dc.setupDecrypt(iv, salt);
byte[] oup = dc.decrypt(enc);
System.out.println("En: "+Arrays.toString(enc));
System.out.println("Ou: "+Arrays.toString(oup));
}
public static final String DEFAULT_CHARSET_NAME = "UTF_8";
private static final char[] DIGITS_LOWER = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
private static final char[] DIGITS_UPPER = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
private static byte[] decodeHex(char[] data) {
int len = data.length;
if ((len & 0x01) != 0) {
throw new UnsupportedOperationException("Odd number of characters.");
}
byte[] out = new byte[len >> 1];
// two characters form the hex value.
for (int i = 0, j = 0; j < len; i++) {
int f = toDigit(data[j], j) << 4;
j++;
f = f | toDigit(data[j], j);
j++;
out[i] = (byte) (f & 0xFF);
}
return out;
}
private static char[] encodeHex(byte[] data) {
return encodeHex(data, true);
}
private static char[] encodeHex(byte[] data, boolean toLowerCase) {
return encodeHex(data, toLowerCase ? DIGITS_LOWER : DIGITS_UPPER);
}
private static char[] encodeHex(byte[] data, char[] toDigits) {
int l = data.length;
char[] out = new char[l << 1];
// two characters form the hex value.
for (int i = 0, j = 0; i < l; i++) {
out[j++] = toDigits[(0xF0 & data[i]) >>> 4];
out[j++] = toDigits[0x0F & data[i]];
}
return out;
}
private static String encodeHexString(byte[] data) {
return new String(encodeHex(data));
}
private static int toDigit(char ch, int index) {
int digit = Character.digit(ch, 16);
if (digit == -1) {
throw new UnsupportedOperationException("Illegal hexadecimal character " + ch + " at index " + index);
}
return digit;
}
}