Little d - Big trouble

Description

The FIPS 186-5 standard requires, in the generation of an RSA key, that the private exponent d be greater than 2**(size//2). The standard also specifies that in the extremely rare case where d is smaller, new prime numbers p and q must be generated.

Try your luck by submitting one of these extremely rare cases.

Files

docker-compose.yml
little-d-big-trouble.py
2.51 KiB – d7964bd1d098a0ae8c6292eb7fc763cb9cb2ec8a08526d22f8614c944b37eea5

Author

Neige

Challenge Instructions

First, download docker-compose.yml:
curl https://hackropole.fr/challenges/fcsc2026-crypto-little-d-big-trouble/docker-compose.public.yml -o docker-compose.yml
Launch the challenge by executing in the same folder:
docker compose up
Then, in another console, access the challenge with Netcat:
nc localhost 4000

⚠️ Important: You must solve the challenge by interacting with the Docker container through the exposed network port. Any other way is not considered valid.

In case you encounter problems, please consult the FAQ.

Flag

You don't have JavaScript actived. No problem! You can check your flag like this: echo -n 'PUT_THE_FLAG_HERE' | sha256sum # possible output: 02afbc94a7443d4ce730c402cb13ea2d0a0233d3819e2ddb1b065735348c298d

Writeups

There are no public solutions for this challenge yet, but you can submit yours after getting the flag.