eprint.iacr.orgpaper

Retention Choices for Quantum CHAM Key Search under a Global Qubit Budget

This IACR eprint paper studies how to allocate a fixed global logical-qubit budget across parallel Grover search workers attacking 80-round and revised 112-round CHAM-128/128, choosing which intermediate round values to retain to minimize circuit depth while meeting a target key-recovery success probability. Testing 83- and 99-set retention libraries against a no-retention/full-retention baseline across 654 budget and Toffoli-decomposition conditions, the authors report mean depth reductions of 11.12% and 8.39% with strict improvements in most conditions, and show retained-value counts don't necessarily scale with budget. The work gives concrete logical-layer resource estimates for quantum attacks on CHAM, relevant to post-quantum migration planning for the lightweight cipher in constrained systems.