In the context of computer security, what does the term "end-to-end encrypted" refer to?
a) A system where data is encrypted only during transmission and decrypted on the receiving end.
b) A method where data is encrypted during both transmission and storage, ensuring it remains secure throughout its lifecycle.
c) A process where encryption is applied solely to data at rest, without affecting data in transit.
d) A technique that ensures data is encrypted only at the initial stage of transmission and decrypted immediately after the first network hop.