Encrypted chain-of-thought blocks returned by frontier APIs are not secrets at all — they are portable ciphertext that the model itself will decrypt, making the model the decryption oracle. Because the envelope is not bound to the request context, an attacker can feed the sealed block back through API calls to recover the full reasoning trace; the attack is a universal jailbreak rather than per-prompt exploitation.
It invalidates the assumption that 'encrypted reasoning in a sealed envelope' constitutes a security boundary. Any design that treats client-visible reasoning ciphertext as opaque and untrusted-but-safe is fundamentally broken; the threat model must assume the model will cooperate with an attacker's replay request.
Whenever a service returns opaque, authenticated-looking blobs to a client and also accepts those blobs back as input, the service's own processing capacity becomes an oracle that defeats the wrapping. This applies to signed state blobs, stateful tool tokens, and delegated capability handles, not just reasoning traces.
Models encrypt thinking and return it in a sealed envelope to the client.
Passing encrypted thoughts back to the model via API calls to extract reasoning.
Universal jailbreak decodes the reasoning of Anthropic, OpenAI, and Google models.