AES-CTR support

[adamreeve]

Hi, I see this question has been raised a few times previously (eg. #693 and #414) but those issues have been closed due to the use cases not being appropriate for ring.

I'm trying to implement support for Parquet modular encryption in the Apache Arrow rust library (apache/arrow-rs#6637).

The Parquet format supports two encryption algorithms, one based on AES-GCM and another that uses a combination of AES-GCM for metadata and AES-CTR for data pages. We have implemented support for reading Parquet files that only use AES-GCM with ring, but it looks like ring doesn't expose a way to use AES-CTR.

Would it be possible to reconsider exposing an AES-CTR implementation for this use case?

[briansmith]

OK, I will reopen #414. Closing this as a duplicate of that one.