Crypto-ncRNA: a bio-inspired post-quantum cryptographic primitive exploiting RNA folding complexity

The imminent realization of fault-tolerant quantum computing precipitates a systemic collapse of classical public-key infrastructure and necessitates an urgent transition to post-quantum cryptography. However, current standardization efforts predominantly rely on structured mathematical problems that may remain vulnerable to unforeseen algorithmic breakthroughs, highlighting a critical need for fundamentally orthogonal security paradigms. Here, we introduce \emph{Crypto-ncRNA} as a biophysically inspired cryptographic primitive that exploits the thermodynamic complexity of non-coding RNA folding as a computational work-factor amplifier. By leveraging the rugged energy landscape inherent to RNA secondary structure prediction, a problem intractable to rapid inversion, we establish a security foundation independent of conventional number-theoretic assumptions. We validate this approach by mapping the folding problem to a Quadratic Unconstrained Binary Optimization model and demonstrate theoretical resilience against quantum optimization attacks including the Quantum Approximate Optimization Algorithm. Functioning as a symmetric key encapsulation and derivation primitive dependent on pre-shared seeds, Crypto-ncRNA achieves throughputs competitive with software-based Advanced Encryption Standard implementations. By utilizing the generated high-entropy keys within a standard stream cipher framework, it exhibits ciphertext entropy that satisfies rigorous NIST SP 800-22 statistical standards. These findings not only articulate a novel bio-computational pathway for cryptographic defense but also provide a rigorous algorithmic blueprint for future physical realization, demonstrating that the thermodynamic complexity of biological systems offers a robust and physically grounded frontier for securing digital infrastructure in the post-quantum era.

💡 Research Summary

The paper introduces Crypto‑ncRNA, a novel post‑quantum cryptographic primitive that derives its security from the thermodynamic complexity of non‑coding RNA (ncRNA) folding rather than from traditional number‑theoretic assumptions. The authors argue that current standardization efforts focus on lattice‑, code‑, and multivariate‑based schemes, which, despite being mathematically hard, remain vulnerable to unforeseen algorithmic breakthroughs or hidden symmetries. To provide an orthogonal security foundation, they exploit the rugged energy landscape inherent to RNA secondary‑structure prediction, a problem known to be computationally intractable when pseudoknots and other topological features are included.

The construction proceeds as follows: a pre‑shared seed is expanded into a random RNA sequence; the sequence is translated into binary codons; a Minimum Free Energy (MFE) secondary structure is computed using O(N³) algorithms such as LinearFold; the resulting base‑pairing constraints are encoded into a Quadratic Unconstrained Binary Optimization (QUBO) model. The QUBO matrix is dense and banded, producing a glass‑like energy surface with many local minima and deep kinetic traps. This structure is deliberately chosen because quantum optimization algorithms—particularly the Quantum Approximate Optimization Algorithm (QAOA) and quantum annealing—struggle to locate global minima in such frustrated landscapes.

To evaluate quantum resistance, the authors simulate a six‑qubit photonic quantum computer running QAOA with one to four mixer layers, incorporating realistic noise (photon loss, decoherence). The attack success probability—defined as finding the exact ground state corresponding to the correct key—is on the order of 2 × 10⁻¹³, effectively negligible. They also analyze Grover‑based search: each oracle query requires a full O(N³) RNA folding verification, which nullifies the quadratic speed‑up normally afforded by Grover’s algorithm. Consequently, even a fault‑tolerant quantum computer would face prohibitive computational overhead.

Key generation exhibits a “structural avalanche” property: tiny deviations in the predicted secondary structure cause massive reordering of the derived bitstream, preventing approximate structures from yielding partial keys. The generated high‑entropy keys are fed into a standard stream cipher (ChaCha20 is mentioned) to produce ciphertext. Comprehensive statistical testing using the full NIST SP 800‑22 suite shows that all 15 tests are passed, with Maurer’s Universal Test yielding a p‑value of 0.85, confirming near‑maximum entropy (≈7.98 bits/byte).

Performance benchmarks compare Crypto‑ncRNA against RSA‑2048 and AES‑256. For a 100 KB block, encryption/decryption takes ~0.19 s, roughly three times faster than RSA‑2048 (0.56 s) and comparable to AES‑256. Throughput scales well across data sizes up to 1 MiB, demonstrating that the O(N³) folding step can be efficiently executed on modern CPUs/GPUs without sacrificing practicality.

The discussion extends the concept to a physical implementation: an ncRNA‑PUF (Physical Unclonable Function). In such a device, the RNA molecule would be synthesized, folded under controlled conditions, and its structure read out via third‑generation nanopore sequencing (e.g., Oxford Nanopore R10.4). The authors acknowledge challenges—sequencing errors, biochemical noise, and environmental variability—but point to recent advances that make reliable readout increasingly feasible. A successful hardware realization would provide a truly unclonable key derived from the stochastic thermodynamic state of a biomolecule, complementing the software “digital twin” presented in this work.

In summary, Crypto‑ncRNA demonstrates that biological thermodynamic complexity can serve as a robust, quantum‑resistant work‑factor amplifier. By mapping RNA folding to a dense QUBO problem, the scheme achieves theoretical resistance to quantum optimization, passes stringent randomness tests, and offers competitive throughput. The paper outlines a clear path from software simulation to physical PUF implementation, suggesting a promising new direction for post‑quantum cryptography that is grounded in physical rather than purely mathematical hardness.