Thanks to anybody replyed to my question :)

Indeed, i have to use core modules except the crypt::Blowfish.
This is the only module additional installed on the machine.

The way radiant.matrix mentioned works fine.

Except one little problem:
The decrypted file contains some characters additional to the original file: ^@
I tried various ways to analyse the problem, but get only a change of the amount of ^@

So please give me a hint: what am i doing wrong?

crypting: 

use Crypt::Blowfish;

my $key = 'ThisIsMyKey';
my $cipher = Crypt::Blowfish->new($key);
my $buffer;
my $file = 'TestFile.txt';
open(my $in,  "<", $file) or die "Couldn't open '$file' for read: $!";
open(my $out, ">", "$file.crypt") or die "Couldn't open '$file.crypt' 
+for write: $!";
while( read($in, $buffer, 8) ) {
        if ( length($buffer) < 8 ) {
                for (1..8-length($buffer)) {
                        $buffer.=chr(0);
                        print length($buffer);
                }
        }
        print $out $cipher->encrypt($buffer);
}

[download]
decrypting: 
my $key = 'ThisIsMyKey';
my $cipher = Crypt::Blowfish->new($key);
my $buffer;
my $file = 'TestFile.txt';
open(my $in,  "<", "$file.crypt") or die "Couldn't open '$file' for re
+ad: $!";
open(my $out, ">", "$file.decrypt") or die "Couldn't open '$file.decry
+pt' for write: $!";
while( read($in, $buffer, 8) ) {
        print $out $cipher->decrypt($buffer);
}

[download]
Thanks a lot, PeterE

In reply to Re^3: Encrypting large files with Crypt::Blowfish by PeterE
in thread Encrypting large files with Crypt::Blowfish by PeterE

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.