Simplifying via Python

Review

Things you’ve learned

Things you've learned

You’ve already solved stages 1 and 2, so you:

  • can erase parts of the flash chip
  • can write data to parts of the flash chip
  • are somewhat familiar with the source code
  • are somewhat familiar with block-based AES cryptography used in ECB mode
  • can check if you’ve progressed via SOLVE command

Definitions:

  • cleartext === original data to encrypt
  • plaintext === data provided to the encryption routine, typically padded
  • ciphertext === the encrypted data corresponding to the plaintext

Programmatic access

Programmatic Access

As I mentioned in the last post, stage 3 essentially requires programmatic interaction with the CTF board communications.

Although not complete, I’d now like to share the helper library I used for this CTF.

Check out the sos_helper repository.

Each stage will have (at least) one module, and there’s a base module that greatly simplifies reading, writing, and erasing the flash.

Each stage’s module has registered commands you can run for that stage … everything from a simple XOR test (for stage 1), ones that walk you through a complex solution (e.g., stage 3), all the way through “autosolve” commands which just bypass that challenge altogether.

The base library and stages 1-2 are already published. I’ll publish the remaining stages as I publish the final steps of the walkthrough.

FIN

With the release of this library, you should have a solid basis for writing your own extensions to investigate and solve stage 3.

My next post will include the deep walkthrough of stage 3 … and it’s a doozy!