# Usage: cypher KEY, LIST;
sub cypher {
    srand shift;
    my $string = join '', @_;
    my $here = 0;
    while ( 2*$here < length( $string)) {
        vec( $string, $here, 16) ^= int rand 1<<16;
        $here++;
    }
    $string;
}

my $encoded = cypher 12345, <<'EOT';
     Listen, my children, and you shall hear
     Of the midnight ride of Paul Revere.
EOT

print map {sprintf '%x ', $_ } unpack 'C*', $encoded;
print $/, cypher 12345, $encoded;