Hi,

You have a couple of problems, here. One is the "\n". The encrypted data is no longer text, so you can't think about it as line- or record-oriented anymore. You're liable to encounter an "\n" byte where you don't expect it, when reading back in the encrypted file (which is now just bytes, rather than ASCII or whatever it was).

You note that you've removed the new-line stuff, and that the script still doesn't work, But if you're still using the <> operator to process your files, then you've still got the record-processing problem in a different form.

DES is a block cipher: it works on data of a fixed length. For DES, the block size is 64 bits. DES expects to be fed 8 bytes of plaintext (64 bits), and will give you back 8 bytes of encrypted data. The Crypt::TripleDES module (like most implementations of a block cipher) will pad short blocks with whitespace.

What this means is that, unless you're being careful to feed only even multiples of 8 bytes to the encrypt3() method, you're not actually encrypting what you think you are. Here is a naive implementation of chunk-by-chunk encrypting/decrypting that does work, although you are left with up to 7 whitespace characters appended to the end of your encrypted-then-decrypted file: 

#!/usr/bin/perl -w
use strict;

# demo usage: ./test-des.pl e some-file.txt | ./test-des.pl d

use Crypt::TripleDES;

my $des = Crypt::TripleDES->new();
my $passphrase = 'hello';
my $operation = shift();
$/ = \8;

while ( <> ) {
  if ( $operation eq 'e' ) {
    print $des->encrypt3 ( $_, $passphrase );
  } else {
    print $des->decrypt3 ( $_, $passphrase );
  }
}

[download]

Note that you really don't want to set the input record separator ($/) to a fixed width of 8 characters in real life, that makes things really, really slow. But you do want to set it to some fixed-width multiple of 8.

If you are bothered by the possible extra whitespace at the end of the plaintext after an encrypt->decrypt round-trip, the usual way to deal with that is to prepend the plaintext size to the message before encrypting it. Then, when you decrypt, you can pull off the size indicator from the front of the data and trim the rest of the message down to that length.

Hope this helps,
Kwin

In reply to Re: Crypt::TripleDES decrypting problem by khkramer
in thread Crypt::TripleDES decrypting problem by sparkyichi

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