Modular Inverses in Python 3 (PicoCTF 2022 #03 basic-mod2)

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[@georgebitounis6532]

For the sake of learning , RSA uses the multiplicative inverse in order to generate the private key (For extra info you know what to do ). John you are a beast , Greetings from Greece !

[@hackvlix]

The "Extended Euclidean Algorithm" is well worth a look, since it is one of the most fundamental algorithms in computer algebra and cryptography, and in particular it is the key to understanding and computing modular inverses.
### Since the gcd of two numbers a,b (suppose a>=b, otherwise swap) is computed step-by-step via the ordinary Euclidean algorithm,
a_0 = a, b_0 = b
for n = 0,1,2... until r_n = 0:
(1) q_n = a_n div b_n
(2) r_n = a_n - b_n * q_n (which implies 0

[@debprasadbanerjee5005]

Rhanks

[@marcusvsilverio]

Hello from Brazil, thank you so much. Awesome video!

[@Feathla]

Thanks John. It’s good to see you’re still learning too. I think it’s helps us feel that it’s ok to always be learning and you can’t know everything. Thanks again for the time and energy you put in.

[@sorav84]

Another golden video from John. He makes looks thing easy and interesting. But the video doesn't show thousand of hours spent learning these skills, approach and thought process.

[@twistedrisers8425]

I like what you did here. I just imported mod_invers from smypy then used modulasinv = mod_inverse(number, 41)

[@rilsan9815]

great approach John!

[@ajithjacob8836]

Awesome, Thanks John.

[@chriskaprys]

John Hammond's channel: come for the infosec lessons & news; stay for the word "shenanigans". 😊

[@marveII0us]

This is so awesome and valuable :DD

[@mathieucartier2678]

Thks !

[@dennismuller1141]

since 41 is a prime number, you could use Fermats little theorem to compute the modular inverse of x by calling pow(x, 39, 41), which works for older python versions as well.

[@gymtraining81]

Nice Nazaré Tedesco image........ Brazil dude!! hahahahahaha love u John...

[@asbestinuS]

Yeah...I love the math...I do the math all the time, I'm the best at math. Thank you for your video, kind sir.

[@guilherme5094]

Awesome John!

[@mirkogambino7991]

loving this series

[@sayChristIsKing]

Dude it such a relief to see that I was not alone crossing my eyes when reading about reverse modulo. I though I was ultra dumb to not getting it right away

[@ramlayassine4639]

def modular_inverse(a, c):
for n in range(c):
if (a * n) % c == 1:
return n
return -1

[@fbmello]

Hello from Brazil 🇧🇷 🖖🏼

[@togrulasgerli1398]

Short but perfect

[@poprivest4715]

Best example of understanding a modular inverse i could find (that actually was my google answer, i just did the search a bit differently lol):
The multiplicative inverse of “a modulo m” exists if and only if a and m are relatively prime (i.e., if gcd(a, m) = 1).
Input: a = 3, m = 11 Output("pow(3, -1, 11)"): 4 Since (4*3) mod 11 = 1, 4 is modulo inverse of 3(under 11)
And not to be confused with 1/3 mod11 (or "(3 to the power of -1) mod11"). I think python did it this way just to simplify it for us. I tried to get a calculator to reproduce the result, to no avail.

[@mossdem]

Thank you so much for doing this. I massively over thought this challenge as simple and straightforward as it turned out to be! I got so frustrated when I couldn't do it but I knew trusty Hohn Jammond would save the day!

[@khannauman7095]

Brother beard looks cool

[@AidinNaserifard]

Great job John👊💜

[@rajeshsagar3912]

hoping that you solve all that pico ctf challenges...thanq

[@blankspace1959]

beautiful

[@magnoelmagnifico957]

When you encrypt a file, does the algorithm apply to the binary directly or other values are used (as shown in the challenge)?

[@Youtupe69]

RSA is not a stream cypher like AES. The encrypted part is always the size of the modulus. So if your mod is 16 bit you need 2 bytes to save the value.

[@Unstable_dio]

seeing the Extended Euclidean Algorithm brought back trauma from a few months ago when i first learned about rsa encryption and tried to compute my own keys, it still not working btw

[@sergeant5848]

It boggles my mind how hackers of yesteryear plied their trade without internet search engines. The accumulative knowledge they had to seek (and remember) wasn't a mouse click away!

[@davsyl94]

I just want to know how to execute the code and the result shows on the right side of the screen and not the bottom!

[@TheDenysabner]

What about @John Hammond using Nazare Tedesco's meme. lol

[@Tkeechy]

Python tutorial when?

[@rajeshsagar3912]

It would help us if you provide the python script

[@Colaholiker]

Seeing that you don't understand the definition of this inverse in your native language makes me feel less bad about not understanding it when reading the definition in a foreign language. ;-)

[@pathfinder750]

comment

[@abdullahalhwaidi6596]

Hi John
I want you help??

[@yurilsaps]

This meme is Brazilian lol