my $key = "this key must be kept secret!";

sub generate_MD5_hash {
    my ( $plain_text ) = @_;
    $plain_text = '' unless defined $plain_text;
    require Digest::MD5;
  return Digest::MD5->new->add( $plain_text . $key )->hexdigest;
}

sub validate_MD5_hash {
    my ( $hash, $plain_text ) = @_;
  return 0 unless $hash;
  return 0 unless defined $plain_text;
  return $hash eq generate_MD5_hash($plain_text) ? 1 : 0;
}

sub decrypt {
    return '' unless $_[0] and $_[0] =~ m!^[A-Fa-f0-9]+$!;
    require Crypt::Blowfish;
    require Crypt::CBC;
    my $cipher = new Crypt::CBC( $key, 'Blowfish' )
    return $cipher->decrypt_hex($_[0]);
}

sub encrypt {
    return '' unless defined $_[0];
    require Crypt::Blowfish;
    require Crypt::CBC;
    my $cipher = new Crypt::CBC( $key, 'Blowfish' )
    return $cipher->encrypt_hex($_[0]);
}