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

# m -- message 
my $m = 'Perl' ;
print "original: $m\n" ;
my $tmpl = 'C*' ;
my @m = unpack($tmpl, $m) ;	   # string -> unsigned char values
print "coded: @m\n" ;

# n = pq -- in RSA, p & q = prime, each 1024 bits/308 digits long
my $p = PARI("prime(".int(rand 50).")") ;
my $q = PARI("prime(".int(rand 50).")") ;
my $n = $p*$q ;			# $n = Pari's obj

# choose a random number r, s.t.
# 	1 < r < (p-1)(q-1) = b
# 	gcd(r, b) = 1 -- relative prime
my $b = ($p-1)*($q-1) ;
my $r ;
do {$r = int rand $b ; } until (gcd($r,$b) == 1) ;
$r = PARI $r ;

# rk = 1 mod (p-1)(q-1) -- k = private key; (n, r) public
my $k = (1/$r)%$b ;		# Pari's math operators, since vars = Pari

# encrypt -- c = (m ^ r) mod n
my @c ;
map { $c[$_] = ($m[$_]**$r)%$n } 0..$#m ;   # Perl: ** for power
print "ciphered: @c\n" ;

# decrypt -- m = (c ^ k) mod n
my @d ; 
map { $d[$_] = PARI("($c[$_]^$k)%$n") } 0..$#c ;   # Pari: ^ for power
print "deciphered: @d\n" ;
print "decoded: " . pack($tmpl, @d) . "\n" ; 


__END__
original: Perl
coded: 80 101 114 108
ciphered: 18431 6512 5843 7236
deciphered: 80 101 114 108
decoded: Perl