A Cryptanalytic Test of the Phaistos Disc as a Protein Sequence

The Phaistos Disc is an undeciphered Minoan-era artifact bearing 242 stamped occurrences of 45 distinct signs. We test whether it encodes one or more protein sequences, with each sign representing an amino acid or post-translationally modified amino acid and the 45 signs mapping many-to-one onto the 20 canonical residues. We treat this as a substitution cipher using a pre-specified battery of methods. Map-invariant statistics disfavor the hypothesis: the disc is more repetitive than length-matched proteins, with a 15-sign exact repeat on Side A, and one sign occurs 19 times, always in group-initial position, a confinement not observed for any amino acid. A Shannon unicity-distance calculation on Swiss-Prot shows that 242 signs are too few to identify a unique map from k-mer statistics. Simulated annealing fails to make the disc more protein-like than optimizer-matched nulls, and a known-plaintext attack against Swiss-Prot finds no decoding that beats a shuffled-disc null in any reading direction. Short stretches can be read as fragments of real proteins, from a woolly mammoth enzyme to a human topoisomerase, but the null predicts such matches by chance. We claim no decipherment and report effect sizes and p-values against matched nulls; the protein hypothesis is not supported.