You travel back in time to meet yourself. How do you know that future you is actually you?

• I have a secret word for just this occasion.
• I make up something on the spot because future me will know it immediately.
• I'll figure it out when it happens.
• Noone else would pretend to be me.
• I don't trust anybody, ever.
• I ask him for the winning lottery numbers.
• I ignore him and instead attempt to create a time paradox.
• Other

Please help with the question. I think it needs a little help.