What is End-to-end Encryption

End-to-end encryption (E2EE) is the encryption of transmitted data across all transmission stations. Only the communication partners (the respective endpoints of the communication) can decrypt the message. When using symmetric encryption, the key to ensure end-to-end encryption must only be known to the end communication partners. When using asymmetric encryption, it must be ensured that the secret key (private key) is in the exclusive possession of the recipient.

The data to be transmitted is encrypted on the sender side and only decrypted again at the recipient. As a result, side-channel information, which is partly generated to control the transmission process, cannot be encrypted, and on the other hand, knowledgeable intermediate stations where the transmitted content is available in plain text is eliminated. End-to-end encryption therefore guarantees complete protection of the transmitted data packets and fulfills three important goals of encryption on the Internet: confidentiality, authenticity and integrity. End-to-end encryption prevents the message from being intercepted by anyone else, including telecommunications providers, Internet service providers, and even the provider of the communication services used.

Usage of End-to-end Encryption

Common technologies for end-to-end encryption are, for example, OpenPGP and S/MIME for e-mail traffic, the Signal protocol, OTR and OMEMO for chat traffic, as well as ZRTP/SRTP for audio/video chats and SIP telephony. A counterpart is point-to-point encryption, with which it can also be used nested in combination.

At a minimum, an encryption method requires that no ciphertext can be decrypted without the secret key. However, this requirement is often too weak because it does not prevent an attacker from obtaining information about parts of the message from the cipher. The well-established security term ciphertext indistinguishability requires that the attacker must not be able to extract any information about the plaintext from a cipher at all, except for the length of the plaintext, which cannot be kept secret.