The best way to do cryptographic agility is to associate the algorithm with the key and negotiate keys (from a given set) only. Google’s Tink library does this

The best way to do cryptographic agility is to associate the algorithm with the key and negotiate keys (from a given set) only. Google’s Tink library does this very well. See https://neilmadden.blog/2018/09/30/key-driven-cryptographic-agility/ https://neilmadden.blog/2018/09/30/key-driven-cryptographic-... for some more background. Version numbers are just algorithm identifiers in another form.