Reflecto Davinciano: a cryptographic cipher in Leonardo da Vinci's portraits

Leonardo da Vinci’s fascination with puzzles, symmetries, and mirrored writing has inspired centuries of speculation about hidden codes in his paintings, but no reports of such verifiable and reproducible systems exist. I report here the discovery of one such cryptographic method that produced readily-indistinct male-female portrait composites distributed across at least ten of his works. Five composites depict Leonardo’s self-portraits paired with the same female subject, at successive life stages. The cipher consists of four keys left in plain sight (paired across two paintings) and comprises three reproducible steps: (1) vertical slicing, (2) horizontal mirroring, and (3) ±30% horizontal scaling (preceded by correcting for a ±30° head tilt if present). Structured analyses combining physiognomic comparison, semantic layering, and redundancy checks reveal convergent patterns consistent with intentional encoding. A conservative joint-evidence model yields a baseline probability of ~60%, which exceeds 99.99% after inclusion of redundancy and negative controls, thus confirming deliberate design. By recovering the first reproducible cryptographic system in Renaissance portraiture and identifying at least five previously unknown autoportraits of his, these findings reframe Leonardo as an artist-engineer who systematically integrated cryptographic designs into his works. The discovery also introduces a generalizable forensic method for authorship attribution and art anti-counterfeiting.