Why Amazon S3 server side encryption (SSE-S3) is misleading

Re:Why Amazon S3 server side encryption (SSE-S3) is misleading by colmmacc on Monday January 16, 2023 @04:09PM (#34405495)

No AWS employee has access to the keys directly from KMS. It's a hermetic system with no operator access like that. KMS Keys are released to AWS services for use based on IAM permissions and grants, and a time-bounded cryptographic pattern we call Forward Access Sessions ... where we end-to-end verify that the requesting service has a recent and legitimate signed request from the customer.

KMS also has the capability to support an external trust store (https://aws.amazon.com/about-aws/whats-new/2022/11/aws-kms-e...) ... where AWS holds no key material at all.

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Re:Why Amazon S3 server side encryption (SSE-S3) is misleading by aborsy on Tuesday January 17, 2023 @02:36AM (#34410041)

It’s a bit like saying I don’t have access to keys in my Yubikey. Sure, but I can decrypt data with those keys.

S3 sends data encryption keys to KMS, and KMS sends back the result: decrypted data encryption keys. So S3 has no access to the master key, but has the data keys in S3 are in RAM for the customer to use.

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Re:Why Amazon S3 server side encryption (SSE-S3) is misleading by colmmacc on Tuesday January 17, 2023 @01:32PM (#34416563)

It's more than what a Yubikey typically does. There are also can't-be-bypassed audit logs of the key usage, and the manner in which S3 is granted access to the data encryption key is very fine-grained; KMS won't allow the S3 systems to decrypt just anything.

The key is stored in memory while it's being used to encrypt/decrypt, that's unavoidable, but humans don't have access to that. Bucket keys are a bit different, where there's a per-bucket key which has a similar scheme and then per-object keys are derived from it as needed. Together with random nonces/IVs, it ends up being a bit of a mini multi-party scheme.

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