Trust Games (lcg2)

cryptohack

Task: a 'prove your trust' game where plaintext, AES key and IV are consecutive byte streams from an LCG (a=0x1337deadbeef, b=0xb, m=2^48) that leaks only top 8 bits per state and reseeds every 16 calls; reproduce the server's AES-CBC ciphertext under the hidden key. Solution: track the call/refresh alignment — the hidden key bytes live in the same 16-state blocks (Block4, Block5) where leaked plaintext[8:16] and IV[0:8] bytes appear; recover each block's 48-bit seed by LLL on the truncated-LCG lattice (40 hidden low bits/state, 8 samples each), predict the key bytes, AES-CBC encrypt and submit.