Re: The security of deflate-compressed streams with uncompressed-length field
John Bowler <[email protected]>
| Newsgroups | gmane.comp.graphics.png.general |
|---|---|
| Message-ID | <CAP7U399kAekscjMxwRw4sMSoWnR8EOGx8WZD51inr8Kcx9sN=A@mail.gmail.com> |
On Sun, Feb 5, 2017 at 12:19 PM, Cosmin Truta <[email protected]> wrote: > On 5 February 2017 at 14:31, John Bowler > <[email protected]> wrote: >> Eh? PNG chunk header: >> [length] >> [chunk-type] > > Incorrect comparison. You really are missing the point of that piece of mine you quote. To write the length before you know it you have to be able to either reliably predict the future or reliably change the past (after you wrote it). In a Turing machine we *can* change the past; we overwrite the tape, or, in this case, we seek back in the output file and overwrite the length. In a Turing machine we cannot predict the future; that is the halting problem. This misunderstanding is why I am so insistent on writing code. Computers are weird, but very exact. Glenn wrote the code and worked out what was happening, just as I did in the past. Machines do what they are told, not what you want, unless, perhaps, it is the same. -- John Bowler <[email protected]> +1 (541) 450-9885 PO BOX 3151 KERBY OR 97531-3151 USA ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot