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From: joven.chiew@gmail.com
Newsgroups: comp.lang.java.programmer
Subject: Encryption problem with CipherInputStream/CipherOutputStream
Date: Sun, 15 Jul 2012 23:59:38 -0700 (PDT)
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Hi I have the following code I tested to encrypt/decrypt file and all is go=
od. It works correctly for full file encryption and now I want to test part=
ial encryption of 100000 bytes. I tried read the 100000 from a text file fu=
ll of "qwerty" text and encrypt it in another file and I am able to decrypt=
 this file back to the 100000 bytes of "qwerty" output to a new test file.

So it seems like the partial encryption is ok, all I need is implement Ciph=
erInputStream to decrypt the first 100000 bytes write to a output file and =
do a normal FileInputStream and write to the output write. Theoretically I =
should have implemented the partial file encryption/decryption.=20

Now, when I open the output file, I saw unreadable character at EOL. What i=
s wrong, how can I correct it?=20

EOF -> "qwertyqwertyqwertyqwertyqwertyqwerty=B1=84w'=E7=F8]uX\=9CaQ2=CBI=F5=
=93=DC=B1=F5=FE=CB=DCTN=B3'"

Cheers.

	public static void encryptFile(SecretKey key, File sourceFile,
			File secretFile) throws Exception {
		byte[] salt =3D new byte[8];
		Random random =3D new Random();
		random.nextBytes(salt);
=20
		final int BUFF_SIZE =3D 100000;
		final byte[] buffer =3D new byte[BUFF_SIZE];
=20
		PBEParameterSpec spec =3D new PBEParameterSpec(salt, ITERATIONCOUNT);
		Cipher cipher =3D Cipher.getInstance(ALGORITHM2);
		cipher.init(Cipher.ENCRYPT_MODE, key, spec);
=20
		InputStream in =3D null;
		OutputStream out =3D null;
		in =3D new FileInputStream(sourceFile);
		out =3D new FileOutputStream(secretFile);
		CipherOutputStream cos =3D new CipherOutputStream(out, cipher);
=20
		try {
			out.write(salt);
			boolean pEncrypt =3D true;
			while (true) {
				synchronized (buffer) {
					int amountRead =3D in.read(buffer);
					if (amountRead =3D=3D -1) {
						break;
					}
					if (pEncrypt) {
						cos.write(buffer, 0, amountRead);
						pEncrypt =3D false;
					} else {
						out.write(buffer, 0, amountRead);
					}
				}
			}
		} finally {
			if (in !=3D null) {
				in.close();
			}
			if (cos !=3D null) {
				cos.close();
				out.close();
			}
		}
	}
=20
	public static void decryptFile(SecretKey key, File secretFile,
			File decryptFile) throws Exception {
		byte[] salt =3D new byte[8];
=20
		final int BUFF_SIZE =3D 100000;
		final byte[] buffer =3D new byte[BUFF_SIZE];
=20
		InputStream bis =3D null;
		OutputStream out =3D null;
		bis =3D new FileInputStream(secretFile);
		out =3D new FileOutputStream(decryptFile);
=20
		bis.read(salt);
=20
		PBEParameterSpec spec =3D new PBEParameterSpec(salt, ITERATIONCOUNT);
		Cipher cipher =3D Cipher.getInstance(ALGORITHM2);
		cipher.init(Cipher.DECRYPT_MODE, key, spec);
=20
		CipherInputStream in =3D new CipherInputStream(bis, cipher);
=20
		int b =3D 1;
		Boolean pEncrypt =3D true;
		while (true) {
			synchronized (buffer) {
				if (pEncrypt) {
						b =3D in.read(buffer);
						pEncrypt =3D false;
				} else {
					b =3D bis.read(buffer);
				}
				if (b =3D=3D -1) {
					break;
				}
				out.write(buffer, 0, b);
			}
		}
		out.close();
		bis.close();
		in.close();
	}