Encryption-at-rest guide says rotating the SSE-KMS key re-encrypts existing model files; KMS key rotation does not re-encrypt stored objects (F-W1-DOCS-TRUST-19) #882

Wave 3 · group W3 Docs · highest severity Medium · 1 finding(s) · effort docs fix

Summary

The guide says ForgeLM is unaffected by key rotation because "the model files re-encrypt at the storage layer". AWS KMS key rotation only changes the key material used for new encryption; it keeps the earlier material to decrypt existing ciphertext and does not re-encrypt stored data. An operator who rotates after a suspected key exposure would believe old model files are protected by new key material when they are not.

Primary finding

F-W1-DOCS-TRUST-19 — KMS rotation is incorrectly said to re-encrypt existing model files

severity Medium · confidence high · checked against the AWS KMS documentation

What happens. docs/qms/encryption_at_rest.md:92-95 (Turkish mirror docs/qms/encryption_at_rest-tr.md:94-97): "rotate the CMK itself, not just the data key. ForgeLM is unaffected by rotation — the model files re-encrypt at the storage layer without the training pipeline noticing." Objects already written with SSE-KMS stay encrypted under the data keys they were written with, protected by the earlier key material; moving them to new key material means re-encrypting them, for example by copying the objects.

Where.

• docs/qms/encryption_at_rest.md:92-95
• docs/qms/encryption_at_rest-tr.md:94-97

Evidence (re-verified on 2026-10-09).

• AWS KMS developer guide, "Rotate AWS KMS keys": rotation changes the key material used for new cryptographic operations, KMS keeps the earlier key material to decrypt data encrypted under it, and rotating key material does not re-encrypt the data the key protects (https://docs.aws.amazon.com/kms/latest/developerguide/rotate-keys.html).
• Both pages are unchanged on development.

Recommended fix. Separate the two operations. Scheduled key rotation protects new writes; existing artefacts stay readable and are not re-encrypted. Re-encrypting existing artefacts — after a suspected key compromise, or where a policy requires it — is a separate step (copy the objects under the new key) and the old key material must stay available until the copy and a restore test are verified. Link the provider's procedure instead of promising transparent re-encryption.

Acceptance criteria

• Neither page states or implies that key rotation re-encrypts existing model files.
• The guide says how existing artefacts are re-encrypted and how long the old key material is kept.
• Documentation listed above is corrected in English and in its Turkish mirror in the same PR.
• The finding is resolved or explicitly closed with a reason.

_{Found by the September 2026 independent review of ForgeLM against commit cab2947 and re-verified against development at f94595f on 2026-10-09. Code links point at cab2947; line numbers may have moved since. Finding IDs (F-W1-…) are stable references for this backlog.}