Even though you can't use Crypt::CBC, you can learn from it's documentation. From said document, the way to pad is one of these: 

 standard: (default) Binary safe
      pads with the number of bytes that should be truncated. So, if 
      blocksize is 8, then "0A0B0C" will be padded with "05", resultin
+g
      in "0A0B0C0505050505". If the final block is a full block of 8 
      bytes, then a whole block of "0808080808080808" is appended.

   oneandzeroes: Binary safe
      pads with "80" followed by as many "00" necessary to fill the
      block. If the last block is a full block and blocksize is 8, a
      block of "8000000000000000" will be appended.

   null: text only
      pads with as many "00" necessary to fill the block. If the last 
      block is a full block and blocksize is 8, a block of 
      "0000000000000000" will be appended.

   space: text only
      same as "null", but with "20".

[download]

You will, of course, need to choose a method, and then make sure to do the *inverse* after decryption. So lets say you choose the 'oneandzeroes' method: 

sub encrypt {
   my $FileHandle = shift;
   my $cipher     = shift;

   my ($buffer, $cyphertext);
   while ( read($FileHandle, $buffer, 8) ) {
      if ( length($buffer) == 8 ) { $cyphertext .= $cipher->encrypt($b
+uffer) }
   }
   # reading is done, now deal with padding of last block
   if ( length($buffer) < 8 ) {
      my $len = length($buffer);
      $buffer .= chr( 8 - $len );
      for (2..$len) { $buffer.=chr(0) }
   }
   elsif ( length($buffer) == 8 ) {
      # we add a full padding block!
      $buffer = chr(8);
      for (2..8) { $buffer.=chr(0) }
   }
   else {
      warn 'We should never have a buffer bigger than 8!!!'
   }
 
   # now encrypt the final block
   $cyphertext .= $cipher->encrypt($buffer);

   return $cyphertext;
}

#___

sub decrypt {
   my $FileHandle = shift;
   my $cipher     = shift;

   my ($buffer, $plaintext);

   while ( read($FileHandle, $buffer, 8) ) {
      $plaintext .= $cipher->decrypt($buffer);
   }
   # trim the padding
   my $last_chunk = substr($plaintext, -8, 8, ''); #removes last 8, to
+o!
   
   # remove for a char followed by a string of chr(00) that's 1-7 long
   # this should be the padding of 'oneandzeroes'
   $last_chunk =~ s/(.)(\x00{1,7})/;

   # check that out to see if it went well
   warn "Trim went all strange!" if ord($1) != length($2);

   $plaintext.=$last_chunk; #put it back
}

[download]

You should probably do things like binmode the files and the like too. Remember, the above examples are just that: examples. You'll need to do more error-handling and test things out yourself.

I am curious why you aren't being allowed to use Crypt::CBC for this, since its implementation is much superior to rolling your own, as it considers all kinds of things you might forget to. I strongly suggest you explain to whomever set that rule that making an exception for Crypt::CBC is a really good idea, as Crypt::CBC and Crypt::Blowfish are really a pair.

<-radiant.matrix->
A collection of thoughts and links from the minds of geeks
The Code that can be seen is not the true Code
"In any sufficiently large group of people, most are idiots" - Kaa's Law

In reply to Re^4: Encrypting large files with Crypt::Blowfish by radiantmatrix
in thread Encrypting large files with Crypt::Blowfish by PeterE

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