Which crypto-algorithem uses iOS in NSDataWritingFileProtection and what is the keysize?

Question

I need to know the crypto algorithm and key strength of NSDataWritingFileProtection. I would like to know the same things for using the Keychain and NSFileManager.

I searched the Apple Developer references:

• Security Services
• NSDataWritingOptions

But found nothing specific.

The Advanced Encryption Standard Algorithm Validation List contains multiple entries of Apple using AES 128bit-256bit but nothing in connection to keychain or NSDataWritingOptions or NSFileManager

Answer 1

Apple themselves use 256-bit AES for their apps, but you can choose from AES, RC4, or 3DES in a variety of key lengths.

See Apple's Certificate, Key, and Trust Services Reference and Cryptographic Services Guide