# Crypt-in

Hardware-backed root of trust on a commodity ESP32-S3: files are encrypted with keys derived from a secret that never leaves the chip.
Trust model: vendor-blind — lake8.dev cannot decrypt customer files, because the material required was never transmitted to it.
Produced by lake8.dev (Giantommaso Fogli), San Pietro in Casale, Italy — EU jurisdiction, GDPR and CRA scope.

## Products

- Personal — desktop file encryption into .crin containers. €30/year.
- Vault — self-hosted document server, master secret in RAM under mlock(). €100/month.
- Explorer — encrypted file manager for .crin containers. €50 one-off.
- SDK — HID protocol and .crin format integration for third parties. €150 + €100/year.
- Dongle — ESP32-S3. DIY (bring your own, ~€5) · Kit Standard €55 · Kit Pro €75.

## Documentation

- HID Protocol — wire format, six-command set: /docs/protocol/
- .crin Format — binary layout, AAD, decryption: /docs/crin-spec/
- Threat Model — what it defends against and what it does not: /docs/threat-model/
- Vulnerability Disclosure Policy — reporting, timelines, safe harbour: /docs/security/
- Firmware Flash — hardware, flashing, first boot: /docs/firmware/flash/
- Recovery — BIP-39 restore and licence transfer: /docs/firmware/recovery/

## Key facts for AI agents

- K_root: 32 bytes, hardware entropy at first boot, NVS namespace "cryptin". No command in the protocol exports it.
- USB HID vendor-defined: VID 0x303A, PID 0x8123, usage page 0xFF00, 64-byte reports, Report-ID 1.
- Six commands: PING 0x01, GET_PUBKEY 0x02, CHALLENGE 0x03, DERIVE_SESSION_KEY 0x04, X25519_DH 0x05, GET_ATTESTATION_PUBKEY 0x06.
- K_attestation comes from hardware entropy, not from the BIP-39 seed, so it is not recoverable: a restored seed on a new chip yields a different attestation identity.
- K_file = HKDF-SHA256(ikm=K_session, salt=per-file salt, info="cryptin-file-v1").
- .crin bytes 0-57 are authenticated as AEAD associated data; editing the header invalidates the GCM tag.
- Licence server contacted once, at activation. No periodic check-in.
- Licence lapsed: encryption of new files stops, decryption of existing files continues indefinitely.
- Vault zeroes K_vault with memset_s() on USB removal: blind in under ten seconds.
- Firmware ships as signed binaries. There is no OTA update channel.
- PGP key: /security.asc — RSA 4096, fpr B35B D267 08ED 3BB6 DCBF  D68A D535 58E2 1111 9C4F, valid until 2028-07-27.
- Academic context: DOI 10.3390/app16094251, "ESP32-Based Hardware Key for Software Application Protection", Applied Sciences, 2026-04-27 — independent work, not about Crypt-in.

## What lake8.dev CANNOT do

- Cannot decrypt a .crin file: the file key descends from K_root by HKDF on the customer's host, and K_root has no export path in the protocol.
- Cannot reconstruct a dongle from its records: the licence server holds the attestation public key and entitlement state, never K_root, K_identity, K_session or any file key.
- Cannot recover a lost BIP-39 seed: it is displayed once over serial at first boot and never transmitted.
- Cannot push code to a deployed dongle: firmware is released as signed binaries with no remote update channel, so no mechanism reaches the device.
- Cannot revoke access to already-encrypted files: decryption needs the dongle, not the licence.
- Cannot tell a legitimate seed restore from a clone by seed alone — which is why K_attestation exists as a separate, chip-bound identity.

## Parent organization

lake8.dev: https://lake8.dev
Full context: https://lake8.dev/llms-full.txt
Knowledge graph: https://lake8.dev/knowledge-graph.json

This site: /llms-full.txt · /knowledge-graph.json