feat(crypto): support directory encryption key rotation#64
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Audit of lib/directory/crypto (closes #56): AES-256-GCM with a random per-call 12-byte IV and verified auth tag is sound. The gap was rotation: ciphertexts carried no way to decrypt under more than one key, so rotating DIRECTORY_ENCRYPTION_KEY would have bricked existing rows. - decryptConfig now tries the current key then an optional DIRECTORY_ENCRYPTION_KEY_PREVIOUS, enabling zero-downtime rotation. - Add scripts/reencrypt-directory-configs.ts (npm run reencrypt:directory) to re-encrypt all stored configs under the current key. - Document the algorithm review, known limitations (sha256 is a normalizer not a KDF; no AAD), and the rotation runbook in docs/encryption.md; note the key-generation guidance in .env.example. - Add crypto unit tests: round-trip, IV uniqueness, tamper rejection, missing-key failure, and previous-key fallback.
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What
Audit of
lib/directory/crypto.tsplus the missing key-rotation support. Closes #56.Audit result
AES-256-GCM, random 12-byte IV per call, verified 16-byte auth tag, stored as
base64(iv|tag|ciphertext). Confidentiality + integrity are sound. Documented limitations:sha256(key)is a normalizer not a password KDF (safe only with a high-entropy random key), and no AAD binding ciphertext to its row.The gap
Ciphertexts had no provision for more than one key, so rotating
DIRECTORY_ENCRYPTION_KEYwould have made every existing row undecryptable.How
decryptConfigtries the current key, then an optionalDIRECTORY_ENCRYPTION_KEY_PREVIOUS→ zero-downtime rotation.encryptConfigalways uses the current key.scripts/reencrypt-directory-configs.ts(npm run reencrypt:directory): idempotent re-encryption of all stored configs under the current key.docs/encryption.md: algorithm review, limitations, and the step-by-step rotation runbook..env.exampledocumentsDIRECTORY_ENCRYPTION_KEY_PREVIOUSand key generation.Closes #56
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