I recently was in need to do AES CBC encryption in a small part of my iOS app and found the _CryptoExtras to be extremely valuable.
I think it should have more exposure since I stumbled upon it by chance after many hours trying to wrap my head around CommonCrypto.
I discovered swift-crypto using Xcode's Add Package Dependencies… window under the Apple Swift Packages collection. I searched for CBC and found it in the source code.
It really deserves to have the underscore prefix removed and be properly documented in the official documentation website: apple.github.io/swift-crypto