# Pastebin G9Xx3fMJ
For the third option, the tx author makes a special change tag their private view key, key prefixing with the transaction's key images to ensure uniqueness and to ensure the change tag can only be used in this transaction.
1. `change_tag = H_16("change_tag", k^v, key_images)`

Upon receipt of the output, and failure of the 48-byte Schnorr proof (implying it may be a change output)
1. `change_tag_nom = H_16("change_tag", k^v, key_images)`
2. Check `change_tag_nom ?= change_tag`, and if it succeeds then whoever made this transaction knew the private view key so the Janus question is meaningless (anyone with an address's private view key can generate all its corresponding subaddresses).