> For the complete documentation index, see [llms.txt](https://polarischain-1.gitbook.io/polarischain/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://polarischain-1.gitbook.io/polarischain/7.-storage-and-persistence-architecture/7.3-encryption-at-rest-and-key-custody.md).

# 7.3 - Encryption-at-Rest & Key Custody

A single operator passphrase activates cryptographic encryption across all persistent stores: consensus RocksDB, application RocksDB, and LMDB hot state. Each data directory maintains an isolated salt sidecar to ensure correct decryption during snapshot restoration or node migration.

| Component            | Algorithm                            | Implementation Notes                                                          |
| -------------------- | ------------------------------------ | ----------------------------------------------------------------------------- |
| Data Encryption      | AES-256-GCM                          | Per-record nonces sourced from OS CSPRNG                                      |
| Key Derivation       | Argon2id                             | Memory-hard KDF, shared securely across stores                                |
| Integrity Validation | BLAKE3 Keyed-Hash                    | Verifies sidecar integrity & key material consistency                         |
| Key Custody Modes    | Plaintext / Encrypted File / Env Var | Encrypted file mode leverages OS keyring; env var mode supports KMS workflows |

**Safety Guarantees:**

* Incorrect passphrase triggers a clean, structured exit with zero risk of state corruption.
* Missing salt sidecar on existing data produces a hard error—the node refuses to silently regenerate salts or re-encrypt with new material, preventing cryptographic downgrade attacks.

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