When you send a message, encrypt it...
...using cryptographic keys
extracted from your own DNA
such that any recipient needs to decrypt it
using cryptographic keys
extracted from their own DNA
which will only match, if they are related to you.
But some may object
"How related?"
Some family members may be very closely related to you, while others may be distant relatives.
Indeed, the whole human family is related.
"How closely related are you looking for?"
"How do you confirm relatedness?"
family?