November 2025
🔒
Security
Challenge Instructions
This month's challenges will be centered around topics like encoding, encryption, hashing, security etc
Here are a few possible ideas, though really it's up to you - feel free to think of your own too!
- Implement a run-length encoding algorithm for either text/emoji strings/images
- Binary to ASCII converter - take 1 byte binary strings like "01000001" and convert them to their ASCII character equivalent 'A'
- Unicode decoder
- Hex encoder & decoder
- Base64 encoder & decoder
- URL encoder/decoder - e.g. spaces " " should be converted to "%20"
- Implement a substitution cipher
- Implement the Caesar cipher
- Vigenère cipher
- Convert text to Morse code and vice-versa
- Create a mapping of some common emojis to words, then use them to write emoji sentences - e.g. "an apple a day keeps the doctor away" would become "an 🍎 a day keeps the 🧑🏻⚕️ away"
- XOR encryption
- Diffie-Helman key generation
- Random password generator
- Password strength checker
- UUID generator
- File encryption
- One-time pad
- DES implementation
- Simple hashing function based on e.g. ASCII values of string and modding by a prime
- Rainbow table generation based on your custom hashing algorithm - show how salting makes rainbow table attacks effectively obsolete (assuming salt remains private)
- ISBN validator
- Luhn algorithm for credit card check digits
- Adler 32 checksum
- File integrity checker - using hashing (checksum)
- Implement a simple 4-digit pin system - crack it using brute force. Then implement security measures (e.g. max of 3 login attempts, time delays etc) to prevent it
- Digital signature using a simple custom algorithm
- Create a simple 2FA system (e.g. by writing a code to a file to simulate an email/SMS message)
- Steganography - hide secret messages in text/files/images etc
- Captcha generator - generate e.g. maths questions, random strings for the user to have to answer correctly
...etc - there are many different examples you can think of
As a target, let's try and have 10 programs submitted by members of the community for others to enjoy...good luck...and have fun!
Top Submissions
Submission Instructions
Create your program on the editor page, then click the upload button at the bottom of the code editor as shown below
Once you are confident your program is working well without obvious bugs, then give it a relevant name, choose the current monthly challenge from the dropdown box, choose some program categories if you want and submit it :)
Note: your submitted programs will be in blue and you can overwrite them by opening them, clicking the upload button again and selecting "overwrite"