Secrets storage to be used in subscriptions

[mfornos]

We will use envelope encryption to store per-subscription secrets safely while keeping the system lightweight.

Keys

Data Encryption Key (DEK)

• One DEK generated per subscription.
• Used to encrypt the subscription’s secret with AES-256-GCM.
• The encrypted secret (ciphertext + auth tag + nonce) is stored in the database.

Key Encryption Key (KEK)

• A single long-lived server key stored locally (env var / file with permissions).
• Used to encrypt each DEK with AES-256-GCM.
• Only the wrapped DEK is stored in the database, never the plaintext DEK.

Nonces / IVs

We will use random 96-bit (12-byte) nonces, generated independently for both KEK and DEK encryption.

Schema / Payload

• Top-level secrets field on subscription input. Users pass secrets on creation only.
• Secrets will never be returned, even encrypted to client requests. We can return a list of secret names only.

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NOTE
We avoid external vault infrastructure, as it would introduce unnecessary complexity at this stage.