Encrypt without password, decrypt only with password
Wouldn't this be just the usual asymmetric encryption, as if you were encrypting e.g. email with GnuPG? 

Create a private key, store it password protected (this is your master password). Anything you need to save, encrypt using the corresponding public key (no need for a password). But only the private key can decrypt your data items, and you need to enter the password to use that.