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Re: A problem with "convert" - security related

Cross-posted to 2 groups.

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Carlos E. R. wrote:
> On 11/11/2018 05.26, Paul wrote:
>> Paulo da Silva wrote:
> 
> ...
> 
>> I agree it doesn't make any sense. Not on writes.
>> It's a reading/interpreting issue.
>>
>> One of the reasons these capabilities existed in the first
>> place, is some laser printers had "resident" fonts. These
>> may have been stored on a hard drive inside the laser printer.
>> At the time, flash (NOR) memory was too expensive to hold
>> the fonts.
>>
>> You could send a specially formulated .ps print job, to send
>> a font to the printer. I've never done it, but heard you
>> could do such a thing at the time.
>>
>> Some file capabilities existed in PostScript, that might not
>> have been there, if it wasn't for the printer requirement.
>>
>> Today, we send embedded fonts in documents, so a printer
>> with resident fonts isn't as necessary. The embedded font
>> is a subset. I have document samples here, where a font table
>> only has one character in it, as an example of how few characters
>> they're willing to embed when sending them with the document.
> 
> All printers, even ribbon printers (pin matrix), have "fonts" :-)
> 
> In some form. They need to handle fonts in order to be able to print
> plain ascii.
> 
> Well, maybe winprinters don't, I do not know.
> 
> Postscript printers have more sophisticated fonts. They can be scaled
> (vector based?) and you do not see the "dots", the quality normally
> keeps. Similarly I think PDF printers also have some fonts, because the
> PDF format assumes the receiver knows how to handle a small set of
> fonts. You can try print directly (raw) a PDF without embedded fonts and
> it should print.
> 
> My printer handles ps and I can send it plain ps files without sending
> fonts and they print fine.
> 

There's a couple ways to print.

The "clumsy" way, is to send a bitmap or pixmap
image of what is to be printed. This usually takes
a bit of bandwidth (but not by todays standards). Back
in the day, we had some pretty bad LAN standards.

The first laser we had at work, didn't have an internal
interpreter. It was a "dumb" printer. It had what
is known as a "video interface". The card feeding it,
sent a 2Mbit/sec video signal. The "image" was then
drawn on the drum as the drum rotated. Print jobs
sent to such a printer, consisted of bitmaps, and
the driver on the computer sitting next to the printer,
would send them out via the video interface.

Later printers, used higher level languages, like
PostScript or PCL or whatever. The printer has
a parser, to read the more compact representation
of a print job, and convert to a bitmap. (One of the
printers had a 25MHz processor, a RISC.) On some
of those printers, the printer didn't have enough
RAM to hold the whole sheet of paper. This
meant that the RAM functioned as a "fraction-of-a-page
buffer". And the parser had to stay ahead of the
print rate, to keep the buffer full. Only rich
companies could afford to put more RAM in the
printer, so an entire glorious page could be
held in RAM. Some of those first machines were
that cheesy.

It's those processor-equipped machines, that
might have a hard drive with fonts. It was an option.
It also means you could make very compact print
jobs. You could tell the interpreter "I'd like to
use Times Roman please". Then specify a character
string and have it rendered immediately at the
current point in space. This is better than having
to download a 2MB font, which on the old networks,
took a while. This worked well enough, we used to
hand-craft PostScript files, while trying examples
from the Red Book.

Rosetta has various tasks written in different languages,
and this is "Hello World" written in PostScript language.

https://rosettacode.org/wiki/Hello_world/Line_printer#PostScript

<</PageSize [595 842]>> setpagedevice  % set page size to DIN A4
/Courier findfont                      % use Courier
12 scalefont setfont                   % 12 pt
28 802 moveto                          % 1 cm from the top and left edges
(Hello world) show                     % draw the string

That example would rely on the printer having
the Courier font onboard. Modern printing tool
chains, probably would not take a chance on that,
and they would send an embedded subset of Courier along
with the print job.

    Paul

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A problem with "convert" - security related Paulo da Silva <p_s_d_a_s_i_l_v_a_ns@netcabo.pt> - 2018-11-10 02:35 +0000
  Re: A problem with "convert" - security related Paul <nospam@needed.invalid> - 2018-11-10 00:15 -0500
  Re: A problem with "convert" - security related stepore <linshine@here.now> - 2018-11-10 00:34 -0800
    Re: A problem with "convert" - security related Paul <nospam@needed.invalid> - 2018-11-10 07:32 -0500
    Re: A problem with "convert" - security related Paulo da Silva <p_s_d_a_s_i_l_v_a_ns@netcabo.pt> - 2018-11-10 17:19 +0000
      Re: A problem with "convert" - security related Paul <nospam@needed.invalid> - 2018-11-10 17:03 -0500
        Re: A problem with "convert" - security related Paulo da Silva <p_s_d_a_s_i_l_v_a_ns@netcabo.pt> - 2018-11-11 02:45 +0000
          Re: A problem with "convert" - security related Paul <nospam@needed.invalid> - 2018-11-10 23:26 -0500
            Re: A problem with "convert" - security related "Carlos E. R." <robin_listas@es.invalid> - 2018-11-12 14:17 +0100
              Re: A problem with "convert" - security related Paul <nospam@needed.invalid> - 2018-11-12 09:21 -0500
                Re: A problem with "convert" - security related "Carlos E. R." <robin_listas@es.invalid> - 2018-11-12 17:09 +0100

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