Encrypting Text with RC4 - Page 12

Encryption and security are becoming commonplace and more important these days. For example, sending your customer's credit card in a clear text e-mail is a big no-no. The RC4 encryption algorithm was invented by RSA and has been widely used for a number of years and is still secure enough for most uses. The Encrypt::RC4 module encrypts a text string with the password that is passed in with the function call. The RC4 function performs both the encryption and decryption routines. When encrypting a string, the first parameter is the password that will be used to encrypt the text. When decrypting an encrypted string, the first parameter is the password that will be used to decrypt the text. The second parameter is the text to encrypt. When running the function to decrypt text, the second parameter is the encrypted text. But enough chatter, let's look at some code that encrypts and decrypts a message.

use Crypt::RC4;
my $encrypted = RC4( $password, $plaintext );
$plaintext = RC4( $password, $encrypted );

The example above encrypts the text contained in $plaintext using the password in $password and assigns the encrypted results to $encrypted. The next line decrypts the encrypted text, given a valid password, and assigns the decrypted text back to $plaintext. The example is a round-trip encryption/decryption routine in two lines of code. Not bad. It shows how simple it is to use, but it's not a practical example, so read on.

This more practical example is executed from the command-line and prompts the user for a password and the file that will be encrypted. It appends the encrypted file with a .rc4 extension.

#!/usr/bin/perl -w
use Crypt::RC4;
print "Please enter a password: ";
chomp(my $password = <STDIN>);
print "Please specify the file to encrypt: ";
chomp(my $file = <STDIN>);
open(FILE,$file) || die "Cannot open $file for read\n";
my $plaintext = join('',<FILE>);
$encrypted = RC4( $password, $plaintext );
open(FILE2,">$file.rc4") || die "Cannot open $file.rc4 for write\n";
print FILE2 $encrypted;

You can use this script to encrypt a file on your system. Of course, this example is only half useful. You'll probably need to decrypt the text at some point, so below is an example that will decrypt an encrypted file.

#!/usr/bin/perl -w
use Crypt::RC4;
print "Please enter the password: ";
chomp(my $password = <STDIN>);
print "Please specify encrypted file: ";
chomp(my $file = <STDIN>);
open(FILE,$file) || die "Cannot open $file for read\n";
my $encrypted = join('',<FILE>);
my $plaintext = RC4( $password, $encrypted );
open(FILE2,">$file.txt") || die "Cannot open $file.txt for write\n";
print FILE2 $plaintext;

The first and second examples are very similar, but the second decrypts an encrypted file. You can use these scripts anytime you need to encrypt sensitive information.

Formatting Text

Do you have to format e-mails, bills, records, HTML pages, and other unstructured texts into a formatted layout? Perhaps you need to spiff up that marketing e-mail so that it's centered. Whatever the requirement, Text::Format is sure to please. Let Perl take on the work you've been doing by hand. This module does a good job of turning messy text into a professionally looking format. And it's easy to use. You can get a listing of the available routines by typing perldoc Text::Format on the command-line (after you've installed it from CPAN).

The sample program below sets the width of the text to 65 characters, sets the left margin to two characters, turns on justification, adds an extra space after periods, and sets the indent to 2 characters.

#!/usr/bin/perl -w
use Text::Format;

my $text = new Text::Format;
$text->columns(65);
$text->leftMargin(2);
$text->justify(1);
$text->extraSpace(1);
$text->firstIndent(2);

open(FILE,"message.txt");
my @message = <FILE>;
$text->text(\@message);
print $text->format();

The format() function is capable of cleaning up badly formatted text and turning it into a well formatted paragraph. To show what it can do, I've pasted the results of a message I passed the script above.

    I am writing to you regarding the free clue that you sold  to
  me last week.  I am sorry to report that I  have  not  received
  any insight into my problems and would like  to  know  if  your
  product has a return policy or can be brought in for  warrantee
  service.

Not bad. Hopefully this means a reduction in the time it takes to fix text by hand.

Processing Text with Perl Modules - Page 11
Weaving Magic With Regular Expressions
Processing URLs - Page 13