All Writeups
Comprehensive collection of CTF challenges, solutions, and insights.
DEADROP Crypto 6 - CIPHER7
Fourstage cryptographic chain, repair a corrupted Reed-Solomon encoded key file, solve the discrete logarithm problem on a backdoored elliptic curve with smooth group order via Pohlig-Hellman, locate a hidden nonce in a binary header, derive the AES key, and decrypt the final briefing.
DEADROP Crypto 5 - DSC-1.1
A fake internal cipher spec documents the agency's homemade DSC-1.1 block cipher, a 2-round Feistel with a trivially invertible round function. Read the spec, implement decryption, and recover the encrypted memo.
DEADROP Crypto 4 - DSA Again?
Two DSA signatures from the same key share an identical r value, a dead giveaway of nonce reuse. Recover the private key, forge a signature over the target authorization message, and submit it to the server.
DEADROP Crypto 3 - oracle_session.py
AES-CBC padding oracle attack against the agency's internal session token system. The oracle reveals one bit per query, valid or invalid PKCS#7 padding, which is enough to recover the full plaintext byte by byte.
DEADROP Crypto 2 - rsa_briefing.enc
RSA encrypted with e=3 and no padding. The message is small enough that m³ < n, so no modular reduction occurs and the ciphertext is simply the exact cube of the plaintext. Integer cube root recovers it directly.
DEADROP Crypto 1 - INTERCEPTED TRANSMISSION 774
Decrypting a Vigenère-ciphered field report by recovering the key from an acrostic hidden in the challenge description, first letter of each sentence spells PIGEON.