Data-at-Rest Encryption, KMS Envelope Keys, and Legacy TLS Instruments

AES-256-CBC is a FIPS-approved cipher, but CBC alone provides confidentiality without integrity. An attacker who can modify ciphertext can flip bits in the decrypted plaintext; the design needs an authenticated mode such as AES-256-GCM or encrypt-then-MAC with a separate key. The bigger problem is key management. A single master key in an application config file is exposed to every operator and backup of that file, provides no separation of duties, no per-use audit, and no hardware protection. Annual rotation does not reduce the blast radius: one key compromise exposes all 38 TB and every tape written under it.

Required changes:

• Use the cloud KMS with envelope encryption: a customer-managed master key in a FIPS 140-2 validated HSM, per-object data keys, and AES-256-GCM for object data.
• Restrict decrypt permission to the application role and log all key use.
• Define key versions and retention for seven years; do not delete old versions until retention expires.
• Use LTO tape encryption with a KMIP-compatible key manager, not an application config secret.
• Separate key-administrator and data-administrator roles.

With those changes the design can meet the contract; the original proposal should not be approved.

First confirm the contract's scope. If it covers only data in transit over untrusted networks and data at rest, the isolated lab segment may be outside the literal requirement, but the security intent still applies because TLS 1.0 is deprecated and has known weaknesses. Do not enable TLS 1.0 on the main load balancer or globally.

Recommended approach:

• Place the instruments on a dedicated VLAN with strict allowlists to a local TLS-terminating proxy.
• Let the proxy accept TLS 1.0 only from those instrument IPs, then re-encrypt to the backend with TLS 1.2 or higher and a modern cipher suite.
• Add IDS/IPS monitoring, restrict the proxy's outbound destinations, and log all sessions.
• Document a time-bound risk exception with the 18-month remediation plan, signed by the data owner and compliance.
• If the contract explicitly covers the instrument-to-proxy hop, escalate for a scope ruling; a proxy does not make TLS 1.0 compliant on that hop.

Compensating controls reduce exposure but do not make TLS 1.0 equivalent to TLS 1.2. The exception must be reviewed before the 18-month deadline.

Use a two-layer hierarchy. The root is a customer-managed KMS key in a FIPS 140-2 validated HSM. For each object, the application asks KMS to generate a data key; it encrypts the object with AES-256-GCM using the plaintext data key, stores the encrypted data key alongside the object, and discards the plaintext key. KMS rotates the root key annually, but old root versions remain available so existing objects still decrypt. This limits each data key to one object and avoids re-encrypting 38 TB on rotation.

For tape, use a KMIP key manager and LTO hardware encryption. Generate a data key per tape or per tape pool, wrap it under a tape key-encryption key held in the KMIP server, and rotate the key-encryption key annually. Retain all key versions for at least seven years plus any legal hold. Destroy keys only after retention and with dual control. Separate the key administrator from the backup operator, and audit every decrypt and key-export attempt. Test restore with an old tape before declaring the design complete.