Artificial Adaptive Control Language (AACL): State-Bound Ephemeral Grammars for Secure Web Actions

Web applications commonly rely on widely deployed defenses such as tokens, headers, and
server-side validation logic to mitigate request forgery, tampering, and replay. While effective
against many threats, these mechanisms primarily establish authenticity and coarse integrity
— validating who is acting and whether they are authorized — but do not formally enforce
the precise structural and semantic contract of individual stateful action instances. This paper
introduces AACL (Artificial Adaptive Control Language), a language-theoretic control framework
in which the server dynamically issues an ephemeral, intent-bound grammar for each sensitive
action instance. Unlike existing mechanisms, AACL defines and enforces the complete acceptable
form of a specific request instance — constraining structure, parameter relationships, state-
bound semantic values, and temporal validity within a single formal acceptance condition. Each
request is treated as a short-lived language instance and validated through formal recognition
grounded in a deterministic finite automaton (DFA) model before execution. In the prototype
realization, the DFA acceptance condition is implemented as key-set equality over intent-specific
alphabets — a tractable and sufficient structural enforcement mechanism for JSON-based web
API payloads. Grammars are state-bound, derived from server-side snapshots at issuance time,
and invalidated after use or expiry, enforcing single-use semantics and preventing replay under
explicit threat-model assumptions. AACL is designed as a complementary enforcement layer
and does not replace authentication, authorization, or transport security — rather, it adds
per-instance structural and semantic intent integrity at the language-recognition layer, addressing
a gap that existing mechanisms such as CSRF tokens, JWTs, nonces, and WAFs do not cover.
We formalize the AACL model, describe its integration into a web application architecture,
and present a prototype demonstrating how ephemeral grammars reduce replay and structural
mutation attacks. Empirical evaluation over 5000 requests confirms linear validation complexity
O(n) and modest latency overhead suitable for high-value, sensitive web operations.

Note: Versions of this paper are polished and refined ones.