What is end-to-end encryption?
End-to-end encryption utilizes a user-generated, private key to encrypt all entries before they reach Day One servers. With possession of the encryption key held only by the end user, maximum security is assured for journal data.

How do I use this feature?
End-to-end encryption is enabled on a journal-by-journal basis. Go to Journals in Day One's Settings, then select the journal you want to encrypt. Follow the on-screen instructions to complete this process. More instructions are found here.