Paper 2025/213 Original: eprint.iacr.org/2025/213 ↗

An Innovative Lightweight Symmetric Encryption Algorithm Integrating Little OaldresPuzzle\_Cryptic

Abstract

Little OaldresPuzzle_Cryptic (LOPC) is specified as a parameterized 128-bit keyed block-transformation core built from three internal components: the NeoAlzette 64-bit ARX-box layer, the XorConstantRotation (XCR) Hybrid8–Shadow round-material generator, and a reversible Key Switch Layer. For every 128-bit data block, the core is invoked with a 128-bit key and a one-time public input number_once; the implementation supports counter-indexed block processing by assigning distinct number_once values to successive blocks. Authentication is not implemented inside the LOPC core: authenticated encryption must be obtained by composing the core with an external MAC or AEAD wrapper. The paper gives a code-faithful specification of the current construction, including the diagonal NeoAlzette placement, XCR-derived round material, keyed switching, and the keyed bit-position tweak. For the NeoAlzette component, it provides local differential and linear MILP boxes, fixed-public arithmetic oracle interfaces, and a mathematical oracle-to-MILP backbone for MEDCP/MELCC-style single-characteristic searches. The current artifact additionally reports one-round 12-hour SCIP incumbent campaigns for differential and linear NeoAlzette characteristics; these are trace/oracle-consistent incumbents, not solver-certified optima. For XCR, it specifies the Hybrid8 byte layer, the zero-fill Shadow arithmetic operators, the non-padded polynomial-Weyl constant stream, and the exact component-oracle boundary; full pseudorandom-generator security of XCR is not claimed. The manuscript separates component-local evidence from composition-level security claims. It proves round invertibility of the specified core and records the current component-analysis infrastructure, but it does not claim a complete AEAD mode, a full PRP/PRG proof for the LOPC composition, or complete endpoint differential/linear hull bounds unless the corresponding endpoint enumeration is explicitly complete. The repository also contains a separate OPC companion block-cipher artifact; Appendix B records its artifact boundary, but OPC is not analyzed as part of the LOPC security claims. Keywords: ARX cryptography, lightweight symmetric encryption, NeoAlzette ARX-box, XorConstantRotation, round-material generation, counter-indexed block processing, keyed switching, shadow-boxed arithmetic, Hybrid8, MEDCP, MELCC, MILP trail search, endpoint HULL, implementation artifact