#!/usr/bin/perl

use strict;
use warnings;
use Math::BigInt;

sub input;

my @id;
push @id, input "Alice's secret key" => 28;
push @id, input "Bob's secret key" => 28;
my $sh=input "the public key" => 50;

my @mid=map $_*$sh, @id;
for (@mid) {
    substr $_, 0,   11 => '';
    substr $_, -11, 11 => '';
}

my ($pwa,$pwb)=map { substr $id[$_]*$mid[1-$_], -55, 10 } 0,1;

print  $pwa eq $pwb ?
  "The passwords match: <$pwa>\n" :
  "The passwords don't match:\n<$pwa>\n<$pwb>\n";

sub input {
    local $\="\n";
    my ($msg,$n)=@_;
    my $m=$n-1;
    print "Please input $msg, a $n digits number, ",
      "or <r> for a random one";
    my $in;
    {
        print '-' x $n;
        chomp($in=<STDIN>);
        if (lc $in eq 'r') {
            $in = 1 + int rand 9;
            $in .= int rand 10 for 1..$m;
            print $in;
            last;
        }
        print "Wrong input, retry" and redo
          unless $in =~ /^[1-9][0-9]{$m}$/;
    }
    print '';
    Math::BigInt->new($in);
}

__END__