End-to-end encryption

End-to-end encryption is a communication design in which only the communicating endpoints hold the keys needed to decrypt message contents. Service providers and network intermediaries can relay encrypted data but cannot read its contents.

Public-key cryptography: Cryptography using mathematically related public and private keys for encryption, decryption, or digital signatures. Public keys can let correspondents establish encrypted communication without sharing a secret beforehand.
Cryptographic key: A value used by a cryptographic algorithm to encrypt, decrypt, authenticate, or derive other keys. Possession and control of the relevant keys determine which endpoints can read messages.
Signal (software): A messaging application that uses the Signal Protocol for end-to-end encrypted conversations. It provides a prominent implementation of encrypted messaging with minimal service access to contents.
Transport layer security: A cryptographic protocol that protects data in transit between networked applications, often terminating at a server. It can secure a connection to a service while still allowing that service to read message contents.
Client-side scanning: Automated analysis of content on a device before it is encrypted or after it is decrypted. Scanning plaintext at endpoints can enable content moderation while changing the privacy guarantees.
Key exchange: A protocol by which parties establish shared cryptographic key material over a communication channel. Endpoints need a secure way to establish keys despite communicating over an observable network.
Digital signature: A cryptographic value that lets others verify a message's origin and integrity using a public key. Encryption does not by itself prove who sent a message.
WhatsApp: A messaging and calling service owned by Meta that uses the Signal Protocol for end-to-end encrypted personal communications. Its deployment illustrates how end-to-end encryption operates at the scale of a global service.
Client-side encryption: Encryption performed on a user's device before data is sent to a remote service. It can protect stored files from a provider, but does not necessarily secure communication between correspondents.
Lawful access to encrypted data: The legal and technical problem of obtaining evidence from data protected by encryption. Providers may be unable to supply message contents even when legally compelled.

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