Is container format relevant to security of encrypted message inside?
Converting the comments to an answer…

Ricky Demer:


  "algorithms used" should be stored with the key(s).  "compression of plaintext used, probably a user supplied tag" should go into the MAC. 


Maxthon Chan:


  That is, algorithm should not appear in the container at all, and everything that is not MAC itself should be included in MAC?


Ricky Demer:


  Yes. Also note that compression may be problematic.


Maxthon Chan:


  I forgot the asymmetrically encrypted symmetric key may appear in the file as well as key.bin. How to deal with that?


Ricky Demer:


  If you're using public keys too, then you should probably use digital signatures, possibly instead of a MAC.