<scp>MusicoCrypt</scp> : A Music‐Modulated Stream Cipher Using Deep Pitch Estimation and Number‐Theoretic Dynamics

ABSTRACT This paper presents MusicoCrypt, a context‐bound music‐modulated stream‐encryption framework that incorporates audio‐derived public side information into a pseudorandom‐function‐centered encryption workflow. A shared reference recording is processed using a pitch‐tracking pipeline, and ordered note pairs are encoded as residues in to form a contextual carrier. We first analyze MusicoCrypt‐Core, a raw affine construction in which HMAC‐SHA256‐derived table indices select Happy‐number and Collatz‐based coefficients for carrier modulation. Motivated by the observed statistical bias of this raw affine stream, we introduce MusicoCrypt‐W, a bias‐resistant variant in which the audio‐derived carrier and affine residue are used as domain‐separated inputs to a final HMAC‐SHA256 extraction layer with unbiased rejection sampling over . A byte‐oriented MusicoCrypt‐WB interface is also defined for binary protocols and standardized bit‐level testing. The evaluation includes long‐sequence stream statistics, HMAC‐only/audio‐hash/carrier ablations, NIST SP 800‐22 bit‐level tests, fixed‐budget extraction analysis, known‐plaintext analysis, frame‐resynchronization simulation, acoustic synchronization experiments under additive white Gaussian noise, and computational‐cost measurements that separate offline carrier extraction from online keystream generation. Results on symbols show that the raw Core keystream remains detectably non‐uniform, whereas MusicoCrypt‐W is consistent with the expected uniform distribution in the reported symbol‐domain chi‐square test. The ablation study shows that HMAC‐based extraction provides the final statistical behavior, while the audio context provides context binding and cross‐context separation. Accordingly, MusicoCrypt is positioned for context‐bound multimedia workflows where offline carrier extraction is acceptable, rather than as a replacement for lightweight real‐time binary stream ciphers.