How to encrypt effeciently large assetbundle encryption?

Hi. I'm trying to some kinds of things to protect my resources.
But I can't find good way for this.

Process that I'm tried.
1. Encrypt assetbundle with random positions.
2. Write encrypt positions information to log file.
3. When I use that assetbundle, read logfile and decrypt, load assetBundle by 'AssetBundle.LoadFromMemory'

This way has many problems.
1. To decryption, I must be load all bytes of file and makes high memory usage.
2. load bytes -> decryption -> AssetBundle.LoadFromMemory is too slow in comparison to AssetBundle.LoadFromFile.
3. Single AssetBundle.LoadFromMemory action is too slower than AssetBundle.LoadFromFile.


What else best way to protect assetbundle?
Or How do you protect your assetbundle?