#! /usr/local/bin/perl -w
use strict;
# --------------------------------------------------------------------------
# 	the essence of RSA algorithm -- assymetrical\public-key cryptography
# -------------------------------------------------------------------------- 
use Math::Pari qw(gcd PARI) ;

my $msg = 'ibm%^&*"<>`' ;

my $cipher = cipher->new() ;
my @c = $cipher->cipher($msg)  ;
print "@c\n" ;
print $cipher->decipher(\@c) . "\n"  ;


{
	package cipher ;
	use strict ;
	use Math::Pari qw(gcd PARI) ;
	
	my ($int, $p, $q, $n, $b, $tmpl) ;		# declared here, or won't share
	
	BEGIN {
		$int = 40 ;
		$p = PARI("prime(".int(rand $int).")") ;	# Pari: prime(n) -- the n-th prime
		$q = PARI("prime(".int(rand $int).")") ;
		$n = $p*$q ;
		$b = ($p-1)*($q-1) ;	# s.t. 1 < e < (p-1)(q-1), gcd(r, b) = 1
		$tmpl = 'C*' ;			# template for pack, unpack
	}
	
	sub new {
		my $class = shift ; my $self  = {} ;
	    # - - - - - - - - - - - - - - - - - - - - - - - - - -
	    do {$self->{e} = int rand $b ; } until (gcd($self->{e},$b)==1) ;
	    $self->{e} = PARI $self->{e} ;		# public key, along with $n
	    $self->{d} = (1/$self->{e})%$b ;	# private key
	    # - - - - - - - - - - - - - - - - - - - - - - - - - -
	    bless($self, ref($class) || $class) ;
	    return $self ;
	}
	
	sub cipher {
		my $self = shift ;
		my @m = unpack($tmpl, shift) ;
		my @c ; map { $c[$_] = ($m[$_]**$self->{e})%$n } 0..$#m ;	# encrypt -- c = (m ^ e) mod n
		return @c ;
	}
	
	sub decipher {
		my $self = shift ;
		my @c = @{shift(@_)} ;
		my @d ; map { $d[$_] = ($c[$_]**$self->{d})%$n } 0..$#c ;	# decrypt -- m = (c ^ d) mod n
		return pack($tmpl, @d) ; 	
	}
}