Privacy-preserving filtering of encrypted traffic via handshake decryption and re-encryption

Abstract

Described systems and methods protect client devices such as personal computers and IoT devices against harmful or inappropriate Internet content. When a client uses an encrypted handshake to hide the identity of the end server, e.g., in applications implementing an encrypted client hello (ECH), some embodiments employ a modified DNS server to provide a surrogate key to the client instead of the genuine handshake key. A traffic filter executing for instance on a network gateway may then intercept and decrypt the handshake and apply an access policy to selectively allow or deny access to the respective end server. When access is allowed, the traffic filter may re-encrypt the server identifier using the genuine handshake key before forwarding the handshake to its destination. Communication privacy is maintained since the illustrated methods only decrypt the handshake, and not the actual payload.