A deterministic wallet takes a single master seed and runs HMAC-SHA256(seed ∥ index) to sequentially produce all 256-bit private keys. He then zeroes out the top i bits and sets bit i–1 to 1, so that exactly i bits are pre-known and the remainder must be brute-forced.

Had he really picked each key manually, he would have needed to record or store 256 hex strings—far more cumbersome than simply remembering one seed and the masking rule. With this method, he can reconstruct all puzzle wallets in seconds—no manual handling required.