Yes that's right. Normally for signatures you would do the final encryption with the receiver's public key creating the same issue as solution #1, but in this c

Yes that's right. Normally for signatures you would do the final encryption with the receiver's public key creating the same issue as solution #1, but in this case you would use the symmetric key: 1. Hash message 2. Encrypt hash using your private key 3. Encrypt again using group's symmetric key There's obviously good reason why symmetric keys don't work, especially in place of solution #2 - would be great to be enlightened on why by the author.