The Spirit Cipher

The Spirit Cipher is an authenticated encryption with associated data (AEAD) construction targeting modern CPUs equipped with hardware AES instructions, with explicit tuning for Apple Silicon M-series. The cipher operates on a 1024-bit state organized as eight 128-bit AES blocks, absorbs two message blocks per state update at a rate of 0.25 AES-rounds per byte, and combines four security properties in a single design: (i) a per-message tweak providing nonce-misuse domain separation; (ii) a forward-secure session ratchet based on a 20-round AES-PRF chain; (iii) a cross-algebra source schedule using arithmetic in the Mersenne prime field F_{2^61 - 1} with odd-prime lane diversifiers; and (iv) the Möbius Pivot - a per-message state rotation to the antipode of the 8-lane ring followed by one counter-seeded state update - which gives each message a unique starting state and breaks integral distinguishers at zero per-byte overhead. On Apple Silicon M-series the construction projects to 5-7 GB/s per core. Thirteen adversarial tests all pass with no detectable bias.