The Letter, the Padlock, and the Suitcase: How Haven’s Encryption Actually Works

Let’s actually simplify this, with a really concrete example: imagine you want to send someone a letter, but you don’t trust the mail carrier. You don’t want them reading what’s inside.

So that person gives you an open padlock (but not the key). You put the letter in a box, lock it with her padlock, and send it through the mail. The carrier delivers the box, but has no way to open it, because only whoever holds the key to that specific padlock can open it.

That padlock she gave you is her "public key." Anyone can have a copy of that padlock and use it to lock things for her. But only she holds the key that opens it — her "private key." No one else can open it, not even you, the one who sent the letter.

What if the letter is too big for the box?

Now here’s a detail: this type of padlock only works on small boxes. If you want to send a big letter (say, an entire journal), it won’t fit in the box. So here’s what you do:

• You lock the big letter inside a suitcase, using a random password you just made up.
• That password (much smaller than the letter) is what goes inside the small box, locked with her padlock.
• You send the suitcase and the box together.

On the other end, she opens the small box with her key, gets the password, and uses that password to open the big suitcase.

Result: no one along the way, not even whoever is carrying the suitcase, can see what’s inside. Only her.

The technical name behind the metaphor

This is the result of using RSA-OAEP for the padlock only she can open, AES-256-GCM for the suitcase where the large content stays locked, and PBKDF2 to turn a password into a real key. Together, this box-plus-suitcase combination has a technical name: a hybrid envelope.