Prekey Bundles: How Encrypted Chat Works When You're Offline
How prekey bundles let encrypted chat work when the recipient is offline: what they contain, how a sender derives a shared secret alone, and the key-substitution risk.
X3DH, Explained: The Handshake Behind Asynchronous Encryption
How X3DH lets two people share an encryption key when one is offline — the four Diffie-Hellman operations, what each provides, and the post-quantum upgrade.