for my $testfn (
    "a/b/c",
    'a\b\c',
    'a:b:c',
    "a[!{(\205)}!].ext",
    "a.ext",
    ){
    printf "( %s )\n\t(%s)\n\n", $testfn , WashFilename( $testfn );
}

sub WashFilename {
    use File::Basename;
    my $basename = basename( shift );
    my $id = $$.'-'.time;
    my( $file, $ext ) = map { unpack 'h*',$_ } split /\./, $basename, 2 ;
    return join '.', grep defined, $file, $id, $ext;
}
__END__
( a/b/c )
        (36.3924-1316599650)

( a\b\c )
        (36.3924-1316599650)

( a:b:c )
        (36.3924-1316599650)

( a[!{(à)}!].ext )
        (16b512b7825892d712d5.3924-1316599650.568747)

( a.ext )
        (16.3924-1316599650.568747)