Use public key cryptography to encrypt a symmetric encryption key. Only those who the symmetric key is encrypted to can decrypt it, and in turn use it to decrypt the content. All existing infrastructure (ie, WoT) for distributing public keys can be used.

This is the scheme I am using in git-annex's encryption. It allows a git repository to treat Amazon S3 as an encrypted git remote on which large files can be stored, rather than checking them into git directly.