Java IO.pdf - Nguyen Dang Binh

if (password.length() < 8 ) {
System.err.println("Password must be at least eight characters
long");
}
try {
FileInputStream fin = new FileInputStream(filename);
FileOutputStream fout = new FileOutputStream(filename +".des");
FileOutputStream digest = new FileOutputStream(filename +
".des.digest");
}
}
// Create the key.
byte[] desKeyData = password.getBytes();
DESKeySpec desKeySpec = new DESKeySpec(desKeyData);
SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("DES");
SecretKey desKey = keyFactory.generateSecret(desKeySpec);
// Use Data Encryption Standard.
Cipher des = Cipher.getInstance("DES/ECB/PKCS5Padding");
des.init(Cipher.ENCRYPT_MODE, desKey);
CipherInputStream cin = new CipherInputStream(fin, des);
// Use SHA digest algorithm.
MessageDigest sha = MessageDigest.getInstance("SHA");
DigestInputStream din = new DigestInputStream(cin, sha);
byte[] input = new byte[64];
while (true) {
int bytesRead = din.read(input);
if (bytesRead == -1) break;
fout.write(input, 0, bytesRead);
}
digest.write(sha.digest());
digest.close();
din.close();
fout.flush();
fout.close();
}
catch (InvalidKeySpecException e) {System.err.println(e);}
catch (InvalidKeyException e) {System.err.println(e);}
catch (NoSuchAlgorithmException e) {
System.err.println(e);
e.printStackTrace();
}
catch (NoSuchPaddingException e) {System.err.println(e);}
catch (IOException e) {System.err.println(e);}
Java I/O
The file is read with a file input stream chained to a cipher input stream chained to a digest
input stream. As the file is read, encrypted, and digested, it's written into an output file. After
the file has been completely read, the digest is written into another file so it can later be
compared with the first file. Because the cipher input stream appears before the digest input
stream in the chain, the digest is of the ciphertext, not the plaintext. If you read the file with a
file input stream chained to a digest input stream chained to a cipher input stream, you would
digest the plaintext. In fact, you could even use a file input stream chained to a digest input
stream chained to a cipher input stream chained to a second digest input stream to get digests
of both the plain- and ciphertext, though I won't do that here.
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