in reply to Re^4: line by line Encryption fun with Crypt::CBC and Rijndael? File Ownership issues? (code)
in thread line by line Encryption fun with Crypt::CBC and Rijndael? File Ownership issues?

Are you sure the file was created using my write_str? The point of this thread was to create an appendable encrypted file format. I proposed such a file format, my encrypter produces it, and my decrypter decrypts it (and only it). 
>perl 700015.pl
Hello World
foo bar

>debug data.enc
-rcx
CX 0040
:
-d100 l40
0100  00 00 00 20 53 61 6C 74-65 64 5F 5F 90 66 5E D2 ... Salted__.f^.
      ^^^^^^^^^^^
0110  88 43 CE 87 E6 FE 44 DA-2C E8 84 FF 2B 2B A1 84 .C....D.,...++..
0120  FD BB 96 89 00 00 00 18-53 61 6C 74 65 64 5F 5F ........Salted__
                  ^^^^^^^^^^^
0130  1F 12 77 C8 38 9A 4B 69-A2 33 51 9D 03 60 50 27 ..w.8.Ki.3Q..`P'
-q

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You seem to be missing the higlighted parts.

700015.pl: 

use strict;
use warnings;


use Crypt::CBC qw( );


my $qfn = 'data.enc';


sub read_bytes {
   my ($fh, $to_read) = @_;
   my $buf = '';
   while ($to_read) {
      my $bytes_read = read($fh, $buf, $to_read, length($buf));
      die("$!\n") if !defined($bytes_read);
      die("Unexpected end of file\n") if !$bytes_read;
      $to_read -= $bytes_read;
   }
   return $buf;
}

sub read_uint32 {
   my ($fh) = @_;
   return (unpack('N', read_bytes($fh, 4)));
}

sub read_str {
   my ($fh) = @_;
   my $length = read_uint32($fh);
   return read_bytes($fh, $length);
}

sub write_uint32 {
   my ($fh, $n) = @_;
   print $fh (pack('N', $n));
}

sub write_str {
   my ($fh, $str) = @_;
   print $fh (pack('N', length($str)), $str);
}


{
   my $key = Crypt::CBC->random_bytes(8);

   my $cipher = Crypt::CBC->new({ key => $key, cipher => 'Blowfish' })
+;

   {
      open(my $fh, '>', $qfn) or die;
      binmode($fh);
      write_str($fh, $cipher->encrypt("Hello World"));
      write_str($fh, $cipher->encrypt("foo bar"));
   }

   {
      open(my $fh, '<', $qfn) or die;
      binmode($fh);
      while (!eof($fh)) {
         print($cipher->decrypt(read_str($fh)), "\n");
      }
   }
}

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(Blowfish was used since I'm having a linking problem with Rjindael. You should get similar results with both)

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Re^6: line by line Encryption fun with Crypt::CBC and Rijndael? File Ownership issues? (code)
by samip (Novice) on Jul 25, 2008 at 17:07 UTC
    Thank you very much for your help. I changed the pack/unpack to little-endian order and that worked. If I have to encrypt something on an outside machine and decrypt it at my end (using the encrypter and decrypter above), do they both have to be the same endian?

    Could I use your recommendation above to encrypt and decrypt large files (about 3 million records) or would you have any suggestions or reference points you could guide me to?

    As a useless side-note: I use Tera Term Pro version 2.3 and sometimes when I 'more' the encrypted and decrypted files, my entire charset on the terminal gets funky.

    Thanks again.
[reply]

      If I have to encrypt something on an outside machine and decrypt it at my end (using the encrypter and decrypter above), do they both have to be the same endian?

      If you store 0x11223344 into the file, you'd rather not read 0x44332211 from the file.

      Thank you very much for your help. I changed the pack/unpack to little-endian order and that worked

      I used 'N', which produces the same encoding on all systems. Why did you change it?

      Could I use your recommendation above to encrypt and decrypt large files (about 3 million records) or would you have any suggestions or reference points you could guide me to?

      The format is efficient for appending records semi-frequently, but it's quite wasteful otherwise. Your 300MB might very well take up 600MB, and it could take a while to decode.

      If you have a write-once-read-often scenario, you'd be better off converting the record file into a normal (single encryption session) file before doing your reading.

      An alternative to the entire approach would be to have a persistent deamon which handles writting to the file (as a single encryption session). This would definitely be better if you had a near-constant stream of records to write.

      my entire charset on the terminal gets funky.

      Programs control the terminal by sending special character sequences in-band. The encrypted data can contain any characters, including some that resemble terminal control sequences.

      more and/or less replace "dangerous" characters with representative glyphs. There's also od.

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        I used 'N', which produces the same encoding on all systems. Why did you change it?

        On one server I couldn't use 'N' or 'Q'. It gave me an invalid-type error. I can understand 'Q' not working, but I am not sure why 'N' did not work. It worked everywhere else.

        I am now trying to decrypt a file that is encrypted using the BlowfishNET 2.1.2 library from http://www.hotpixel.net/software.html using the BlowfishSimple class. (The people encrypting the file don't use PERL, but I do.) The README for the above-mentioned says:

        "For efficiency the given string will be UTF-8 encoded and padded to the next 8byte block border. The CBC IV plus the encrypted data will then be BASE64 encoded and returned as the final encryption result."

        Based upon my understanding so-far I am trying to use the following approach to decrypt the data without success:

        • Decode using MIME::Base64::decode. I am unsure here as to whether I have to decode the entire file or 57 bytes at a time. Would you have any suggestions?
        • Read 8 bytes at a time and decode the string using utf8::decode($string). In your read_uint32, I'm changing return (unpack('N', read_bytes($fh, 4))); to return utf8::decode(read_bytes($fh, 4));

        Thank you very much for your help and comments.

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