How does end-to-end encryption work and why does the master password never leave the user's device?

End-to-end encryption or zero-knowledge architecture is the gold standard for modern cloud data storage services and password managers. The main idea of this approach is that the service provider's servers have no technical ability to read user data, as decryption occurs exclusively on the client device.

When a user creates an account in a secure service, their master password is never transmitted across the network in plaintext and is not stored on a remote server. Instead, the device performs local cryptographic computations. A secret encryption key is generated from the master password with the addition of a unique salt using resource-intensive key derivation functions.

The master key obtained in this way is used to encrypt and decrypt the entire database directly in the RAM of the user's computer or smartphone. Only encrypted blocks of information, which look like an unreadable set of characters, are sent to the server. Even if the company's data center is compromised and attackers gain full access to the databases, they will not be able to decrypt the records without knowing the original master password.

This level of security imposes certain obligations and risks on the user themselves. Since the server does not store the master password and has no mechanisms to recover it, losing this secret combination means the irreversible loss of access to all encrypted data in the vault. Services intentionally avoid backdoors and loopholes in the code to eliminate the possibility of forced or illegal data decryption by intelligence agencies or hackers.

To restore access, developers use alternative methods, such as generating emergency secret keys or a recovery phrase during initial account setup. The user must print or securely store this phrase separately from digital devices in order to be able to restore the encrypted storage in case of breakage or loss of the primary gadget.