Cryptographic Proof That Your LLM Never Saw Real Data

Every PII protection tool makes the same promise: "We sanitized it before sending." But promises aren't proof. When a regulator asks you to demonstrate that patient names never reached OpenAI's servers, "trust us" isn't an answer. We just shipped CloakLLM v0.3.2 with cryptographic attestation - Ed25519-signed certificates that mathematically prove sanitization happened. Here's how it works, why it matters, and how to use it. The Problem: Trust Without Verification Most PII middleware operates on trust. You install it, it sanitizes prompts, and you believe it did its job. Your audit log says "sanitized 3 entities at 14:30:00." But that log is just text. Anyone with file access can edit it. Nothing ties the log entry to the actual data that was processed. This creates three gaps: Gap 1: No proof of execution. Your compliance team can show the tool is installed. They can't prove it was running when a specific prompt was sent. Gap 2: No tamper evidence on individual operations. Hash-chaine