The proposal, called QSB, uses hash-based cryptography built on RIPEMD-160 pre-image resistance — a function that quantum computers can only attack via Grover's algorithm, which yields a quadratic rather than exponential speedup, leaving approximately 118 bits of effective pre-image security and 78 bits of collision resistance at the recommended configuration. Transactions using the scheme cost $75–$150 in GPU compute, work entirely within legacy script rules, and can be submitted directly to miners willing to process them without routing through normal mempool infrastructure. The scheme protects newly created outputs only and does not retroactively secure the estimated 4 million BTC held in legacy P2PK addresses — the format most vulnerable to a future capable quantum adversary. Levy describes QSB explicitly as a last-resort contingency measure rather than a substitute for a forthcoming protocol-level upgrade, noting it cannot be used with the Lightning Network.