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Technical Briefing: Closing the ECH Handshake-Size Side Channel in NGINX Problem Statement Encrypted Client Hello (ECH) encrypts the inner ClientHello—including the real SNI—and pads it. But the server's encrypted handshake flight (EncryptedExtensions, Certificate, CertificateVerify, Finished) still exposes its TLS record lengths on the wire. TLS 1.3 encrypts record contents but not lengths, and the dominant record is the certificate chain, which differs per virtual host. This means an observer…