Encryption of large file

Question

Hi all
I have a problem while encrytion of large file
it is giving me ---.length... exception can anyone help
me with code. Or just suggestion is also file
Regards
Raj..

Answer 1

Well it is important to know what encryption scheme you are using. Large
files should not be encrypted using an Asymmetric algorithm such as RSA.
Instead you should use DES, DESede, AES, Blowfish, etc... These algorithms
are designed to encrypt large datasets. The problem with these algorithms
in their natural form is that they require a secret key to both encrypt
and decrypt that must be maintained if you ever wish to decrypt the files.
A good way to overcome that is to use PBE or Password Based Encryption.
I believe the SunJCE provider provides PBEwithMD5AndDES-CBC which conforms
to the PKCS#5 spec. It also provides PBEWithSHA1AndTripleDES-CBC which
closely conforms to the PKCS#12 spec. Other providers provide different
key derivation/cipher pairs to use with PBE. But they all basically take
a password and use that password to create a key that can be used for
encryption/decryption. Aka you don't have to store the key but rather
just remember the password.
Of course you could always use some enveloping method to create a secret key
and then encrypt that secret key with RSA or something then wrap it all up in
some sort of ASN encoding maybe along the lines of PKCS#7. But that is not
really explainable on these boards if you do not know what I am talking about.
I recommend PBE. Its the easiest.
byte[] salt = {
(byte) 0xab, (byte) 0xbb, (byte) 0x4f, (byte) 0x32,
(byte) 0x56, (byte) 0x25, (byte) 0xee, (byte) 0xc1
PBEKeySpec pbeKeySpec = new PBEKeySpec(password.toCharArray());
SecretKeyFactory skf = SecretKeyFactory.getInstance("PBEWithSHA1AndTripleDES-CBC");
Key key = skf.generateKey(pbeKeySpec);
PBEParameterSpec pbeSpec = new PBEParameterSpec(salt,2048);
Cipher c = Cipher.getInstance("PBEWithSHA1AndTripleDES-CBC");
c.init(Cipher.ENCRYPT_MODE, key, pbeSpec, rand);
CipherOutputStream co = new CipherOutputStream(nwe FileOutputStream(outFile), c);
FileInputStream fis = new FileInputStream(fileToEncrypt);
byte[] buf = new byte[1024];
int len = 0;
while((len = fis.read(buf)) != -1) {
co.write(buf,0,len);
co.close();
fis.close();
To decrypt ...
byte[] salt = {
(byte) 0xab, (byte) 0xbb, (byte) 0x4f, (byte) 0x32,
(byte) 0x56, (byte) 0x25, (byte) 0xee, (byte) 0xc1
PBEKeySpec pbeKeySpec = new PBEKeySpec(password.toCharArray());
SecretKeyFactory skf = SecretKeyFactory.getInstance("PBEWithSHA1AndTripleDES-CBC");
Key key = skf.generateKey(pbeKeySpec);
PBEParameterSpec pbeSpec = new PBEParameterSpec(salt,2048);
Cipher c = Cipher.getInstance("PBEWithSHA1AndTripleDES-CBC");
c.init(Cipher.DECRYPT_MODE, key, pbeSpec, rand);
CipherInputStream co = new CipherInputStream(nwe FileOutputStream(encryptedFile), c);
FileOutputStream fos = new FileOutputStream(plainTextFile);
byte[] buf = new byte[1024];
int len = 0;
while((len = fis.read(buf)) != -1) {
co.write(buf,0,len);
ci.close();
fos.close();
Of course to be even more secure you would need random salt. But then you
would have to retain that in order to decrypt.