If I want to encrypt a text content file using a symmetric algorithm like AES, is there a standard format gpg will expect, where it can detect a symmetric key (encrypted with recipient gpg public key RSA) in my output? E.g. should the encrypted key be a fixed length field at the beginning of my output?
I am not able to use a suite gpg tools or command line. I am restricted to manually using a subset of cryptography APIs supported in a legacy system.
But I am struggling to find any reference that would help me manually construct an appropriately structured "package".