SECURITY
Solving a layered cryptographic puzzle
I solved the first stage of a team cryptography challenge, revealing the instruction needed to continue to password derivation and RSA decryption.
- 26 Caesar shifts · 3 Vigenère keys · 24 column orders
Turning an unknown cipher into a testable problem
My part of the team challenge was to identify the transformation used in Stage 1 and recover the instruction needed for the next stage. I approached it as a bounded search problem, comparing candidate decryptions rather than guessing a single method.
The search covered the 26 possible Caesar shifts, three supplied Vigenère keys, and all 24 orderings of four transposition columns. A shift of 11 revealed the next instruction. That result was the handoff to my teammates, who completed password derivation, RSA decryption, and signature verification.
My contribution
I focused on Stage 1: testing all 26 Caesar shifts, three supplied Vigenère keys, and the possible four-column transposition orders. I identified a Caesar shift of 11 that revealed the next instruction.
The output
A Caesar shift of 11 revealed the next instruction. My teammates used it to derive the password, decrypt the final message, and verify its signature.
Try a Caesar shift
The text box starts with a synthetic example from the Stage 1 repository. Move the slider to change how far each letter shifts backward through the alphabet. At 11, FDP ESP VPJ becomes USE THE KEY. Try a neighboring shift to see how the result changes, or enter another short ciphertext. This demonstrates the Caesar operation only, rather than the full team challenge.