Python Scripting Modular Arithmetic - PicoCTF 2022 #02 basic-mod1

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📧Contact me! (I may be very slow to respond or completely unable to)

[joeymelo]

Hey John. I’ve been following you for over a year now. It’s crazy that I remember watching your videos and being bombarded with knowledge. So much I didn’t understand or never considered.

Now, moving forward to today, I was able to switch careers and get a pentesting job, and I’ve grown so much. And now that I’m watching your video on picoCTF I’m thinking: “man, that’s such a basic/easy challenge”. I almost can’t believe these types of challenges would take me forever a year ago and I had to look up writeups constantly.

My point is, I wanna thank you for taking the time and go over the details in these beginner-friendly videos. Things like explaining what “ls” is doing or the difference between “int” and “str”. That’s gold for those who are beginning. I can see how much I’ve grown professionally and I’m certain this will also be of help to so many students out there.

You rock!

[franktejeda]

I have never 110% understood a Python video in my life before until now, Everything made so much sense and was beautifully explained (I'm a noob btw) I would absolutely love to see more Python videos with these explanations in the future

[seanvinsick]

Avoid ifs if you can. Strings are char arrays, so create a string of all the characters you want to map. Use its index to look up the value.

Table = "ABCD ... _"

encodedvalue = table[value % 36]

[JeffNoel]

The fact that you explain all your keyboard shortcuts is worth its weight in gold.
I love how you say out loud what you're thinking, showing a basic way and then simplify/optimize the code.
Thanks a lot for publishing all these PicoCTF videos.

[arandomboredindividual]

Been loving this series. Keep it up man!

[guydht]

That f-string didn't work because the inner string quotations you used for the join ("".join()) is the same as the outer f-string quotations. If you had written down f'picoCTF{{{"".join(flag)}}}' it would've worked

[renanzinx]

Josh, you content is so good.. such a pitty that I'm not studying for security jobs. I wish I knew someone in devops world with a quality of content like yours

[_CryptoCat]

curly braces with mv command 😮 learn something new every day 👌

[jekyll]

I wish I had 10% of your capacity of explaining the technical concepts so clear

[joeyshi]

I find it's often simpler to define a string with the character set like CHAR_MAP =
Then, mapping a single `val` becomes as simple as CHAR_MAP[int(val) % len(CHAR_MAP)].

- I use len(CHAR_MAP) here because this makes things easier if we ever wanted to extend our character set.

[sasakanjuh]

Hey John, really not trying to be that guy who comments how things could be done better, just want to point out you could use += sign to concatenate string to the variable rather than using list and join method :) Keep up an amazing work, as always!! :)

[fjrgo]

Thanks for explaining the python code for the non programmers! Appreciate it.

[KramerEspinoza]

Why not add string.ascii_uppercase + string.digits + ‘_’ use that as your map and get rid of the if then else otherwise

[drewzilla]

Great series! I am attempting each challenge myself first and then coming here to watch the video on it. Love the outro music as well.

[dtvdavid]

Thank you for teaching these things, it really helpful for beginners!

[jpiercelt]

Libraries to the rescue again! I tried to use this whole fancy match-case thing that came with python 3.10, but apparently I need to read up more on the syntax. Yours is way cleaner, and better! Thanks for the lesson once again John, these are *GREAT!*

[TheDutchisGaming]

13:10 seems like I learned something today. Never knew such for statements were a thing.

[Colaholiker]

It would probably be too high of a python level for the intended audience, but I would have started building a combined string of string.ascii_uppercase + ascii.digits + '_', , and then generated the characters in a single instruction inside the list comprehension

translate = string.ascii_uppercase + string.digits + '_' # Todo: Find better name for this ;-)

# (...) Read file into variable named content
characters = [translate[int(x) % 37] for x in content.split()]

Now all that is left to do is join the items of the list "characters" into the flag string.

The benefit is that we don't need to go through the if/else statements and we don't need to worry about getting the index straight for the digits.

[FVT-tnji]

Thank you for explaining all of this in such detail! Really interesting as always :)

[karenruvalcaba]

I cannot thank you enough for explaining the little things. For once I'm really understanding the material.