Back in 1993, I was taking a number theory class • Hacker News Board

Re: Back in 1993, I was taking a number theory class

#181

Post by GnarfGnarf » Tue, May 04, 2021, 2:19 PM UTC

In 1967, while I was in school, I reverse-engineered the Montreal Metro system transfer tickets. It used a custom paper tape-type punched code. I was able to manufacture tickets. Was real popular with my classmates.

In 1983 I reverse-engineered the Xerox 9700 laser printer font format. Xerox were real SOBs and refused to share technical info with their customers, who were paying $12K/mo rent on the huge printers (120 impressions/min., two-sided). I altered random bits in the font files, and displayed the distorted results. My apotheosis was selling new fonts to the local Xerox branch.

Re: Back in 1993, I was taking a number theory class

#182

Post by tzs » Tue, May 04, 2021, 2:46 PM UTC

kqr wrote: post #150

a3n wrote: post #146

Earlier quoted context omitted.

> I would like to politely contest the authenticity of this specific detail. > People's natural mental sorting algorithm is most often insertion sort. [embarrassed panic] [trip down wikipedia lane] No, it was bubble sort. Data and loop management for insertion sort wouldn't have been something I would have thought of back then.

What confuses me is that isn't the data and loop management for bubble sort even more complicated? Insertion sort is literally just "keep track of the index beyond the last sorted element, then scan for the next smallest element and swap it in, repeat until you have gone through the entire array." This is about as simple as a comparison sort gets. (And it's what literally everyone I've watched does when they get deal…

> Bubble sort, on the other hand, requires you to reason about consecutive adjacent swaps, keep track of whether the current iteration dirtied the array, and so on.

You only need to keep track of whether or not the current iteration dirtied the array if you want to stop as soon as a pass leaves the array sorted. If you don't want to do that (or don't think of it) then it is just something like:

  for pass = 1 to n
    for index = 1 to n-1
      if array[index-1] > array[index]
        tmp = array[index]
        array[index-1] = array[index]
        array[index] = tmp

There is less extra to keep track of then in insertion or selection sort.

Re: Back in 1993, I was taking a number theory class

#183

Post by preston006 » Tue, May 04, 2021, 2:58 PM UTC

Back in high school (which wasn't really all that long ago) just about every computer on the network had really a massive set of content and program restrictions, but it was all very surface level. Very little security if you knew what you were doing, and thankfully the login script that was used for your district-wide account, was run in Powershell.

Not nearly as interesting as OP's hack here, but there was plenty that you could do if you just knew what to use Powershell for. When the machines got upgraded to Windows 10 from 8, every computer you logged into would use the Win10 default background instead of the blank blue one they used previously, and when in my CS class I found it rather distracting. Of course I went over the top, and since you were disallowed from changing the background picture in settings, or with the right click menu, I created a little tool my freshman year to change the value of the my user account's registry key for the background, to whatever else I wanted.

I understand IT's reasoning against giving highschoolers that access (preventing sexually explicit backgrounds), but I just wanted a nice winter landscape, and so when they eventually caught wind they didn't really mind, though they did give me the 'with great power comes great responsibility' speech.

Through my next three years the tool grew to give me command line access, bypass certain parts of the filter, be able to play a bit of music over a pair of headphones, the works, and I was always the cool guy with the one non-standard background in class. It probably looked much more like I was "Hacking the mainframe" than what I was doing in reality, playing MUDs during boring presentations via telnet.

Re: Back in 1993, I was taking a number theory class

#184

Post by bdwjn » Tue, May 04, 2021, 3:04 PM UTC

elengyel wrote: post #19

I'd like to clarify that my code was running only on machines that were otherwise idle. Not many people were in the lab late in the evenings. MPQS processing nodes could be added and removed dynamically, so if somebody needed a computer that was part of my cluster, they could just quit my program and everything would go back to normal. Also, once the number theory professor learned of what I had implemented, he worke…

Ah, good times. Our lab ran sshd on each workstation, so I launched cli processes on every system, at daytime, with dozens of students still working on their project. I thought running as "nice -n 19" would be safe.

Wrong. My program ran out of memory, systems started thrashing, desktops froze up. Confused students, panicking about unsaved changes, swearing, rebooting. Meanwhile I was frantically trying to kill my processes, but even sshd became unresponsive so I couldn't stop the madness. They never found out it was me :)

Re: Back in 1993, I was taking a number theory class

#185

Post by 2sk21 » Tue, May 04, 2021, 3:29 PM UTC

exikyut wrote: post #128

2sk21 wrote: post #38

I have a similar story but I was not quite so clever. Back in 1990 and 1991, I used a cluster of IBM RS6000 workstations in my university to train neural networks. I had previously tried to get backpropagation to work on a Connection Machine but found it too frustrating to work with. The cluster of RS6000s actually ran my code (written in C) very fast and was able top get some good results and graduate with PhD. I bu…

Do you remember why the CM was so frustrating? That's a very ironic story right there.

Main problem was that it was hard to get time on our CM2 to run jobs. You had to sign up in advance and it was a nuisance. Also debugging the parallel version of C for the CM2, called C* was pretty hard to debug as well.

Re: Back in 1993, I was taking a number theory class

#186

Post by 2sk21 » Tue, May 04, 2021, 3:30 PM UTC

eps wrote: post #132

2sk21 wrote: post #38

I have a similar story but I was not quite so clever. Back in 1990 and 1991, I used a cluster of IBM RS6000 workstations in my university to train neural networks. I had previously tried to get backpropagation to work on a Connection Machine but found it too frustrating to work with. The cluster of RS6000s actually ran my code (written in C) very fast and was able top get some good results and graduate with PhD. I bu…

There used to be something called PVM - Parallel Virtual Machine - a fairly simple library for distributed computing. Had to use it once back in Uni, it wasn't bad. Edit - http://www.csm.ornl.gov/pvm/

Yes PVM would have been great had it been available but as I recall, it came out later, in the mid 90s.

Re: Back in 1993, I was taking a number theory class

#187

Post by zsmi » Tue, May 04, 2021, 5:42 PM UTC

Amazing how times have changed. Took just over 15s inside Mathematica on an old Intel MacBook Air with dozens of other apps running. Didn't even spin the fans up.

  In[*]:= Timing@FactorInteger[RandomInteger[{10^70,10^71}]]
  Out[*]= {15.2956,{{2,1},{7,1},{37515320305457999,1},{326028473853489650357,1},{311862636985416087931035845158981,1}}}

Re: Back in 1993, I was taking a number theory class

#188

Post by linux_is_nice » Tue, May 04, 2021, 6:21 PM UTC

throwaway3699 wrote: post #121

knodi123 wrote: post #48

Earlier quoted context omitted.

Ah, the era of primitive DIY security. Those were the days. It's kinda of sad that today's kids have to deal with industry-grade encryption and professional best practices, instead of going toe-to-toe with an underpaid self-taught middle-aged "computer guy" like my generation did...

I had a few amusing tactics. Even with 'professional best practices' (debatable), the human element was still vulnerable. One example was that my school refused to give out the Wi-Fi password as a form of security, so they'd demand to manually type it in themselves on your machine. A simple keylogger and now the whole school just ignored that rule for a few months. Another is that while they tried to block things lik…

Hilariously, I'm thinking of doing that(using SSH over port 80) at my school.

Re: Back in 1993, I was taking a number theory class

#189

Post by WalterBright » Tue, May 04, 2021, 6:44 PM UTC

dreamcompiler wrote: post #178

WalterBright wrote: post #67

Earlier quoted context omitted.

In the same time frame, I worked at Boeing doing design work on the 757. I didn't know how to do complex numbers using drafting tools, but I knew how to use a computer. The only computer in the building was an '11 in a special locked room with raised floor and A/C. It was under the control of Boeing Computer Services, a totally separate division from Boeing Commercial Airplane Company, which I worked for. Anyhow, I b…

> hand them off to the secretary pool to type up This brought back a memory. In the late 80s I got a job at a very high-tech science and engineering firm. A colleague told me to be careful about writing code. His supervisor had walked by his office one day and saw him writing code on a terminal. He chewed him out for "typing" because "typing is for secretaries." Apparently the correct procedure was to hand-write your…

When I started using the Wang, I did get a bit of ribbing for doing "women's work". I laughed at that, and it didn't happen again.

Heck, I'd been using a computer to write my papers in college (using DECUS' runoff program, similar to Unix's man formatting program).

I can't remember the last time I hand wrote more than a few words.

Re: Back in 1993, I was taking a number theory class

#190

Post by mywittyname » Tue, May 04, 2021, 7:18 PM UTC

ecshafer wrote: post #78

vuciv1 wrote: post #4

Earlier quoted context omitted.

I graduated last year, and I worked for my colleges IT department. We used to have to come knocking at the door if a student even had their own printers set up. It definitely would not go well. That being said, I did know people who clogged the cs department's machines with batch jobs to train really expensive ML models that did God knows what. Its not the same as bypassing a security system, but it is an instance of…

I couldn't imagine a situation where if someone knocked on my dorm room door asking if I had a printer in there, I would not have told them off with very unflattering language and telling them to perform fellatio upon themselves. How many students are just rolling over and saying sorry? I would imagine most would give you a very hard time.

> How many students are just rolling over and saying sorry?

Probably most/all. IT infrastructure is critical and there's a very good chance that the IT staff have a process in place for dealing with kids who won't let them do their jobs. And it's probably a pretty effective process that has been refined over the past decades.