Understanding HTTPS Performance Overhead

The theoretical performance overhead of HTTPS stems from additional operations required for secure communication. The TLS handshake adds round trips between client and server before data transmission can begin. Encryption and decryption operations consume CPU cycles on both endpoints. Certificate validation requires additional processing and potentially external OCSP lookups. These overheads are real but have been dramatically reduced through various optimizations.

Modern hardware includes dedicated instructions for cryptographic operations, making encryption overhead negligible for most workloads. AES-NI instructions, available in most processors since 2010, accelerate AES encryption by 3-10x compared to software implementations. Elliptic curve cryptography operations benefit from similar hardware acceleration. Even mobile devices now include cryptographic acceleration, eliminating performance concerns for client-side encryption.

The TLS handshake represents the most visible performance impact of HTTPS, adding latency to connection establishment. TLS 1.2 requires two round trips for full handshakes, adding 50-200ms depending on network latency. However, session resumption reduces subsequent connections to one round trip. TLS 1.3 improves further, requiring only one round trip for full handshakes and supporting zero round-trip resumption for returning clients. These optimizations significantly reduce the perceived performance impact.

Certificate validation overhead has been addressed through OCSP stapling and certificate caching. Traditional OCSP lookups added latency and privacy concerns as browsers contacted CA servers during connection establishment. OCSP stapling allows servers to include cached OCSP responses in the handshake, eliminating external lookups. Certificate caching prevents repeated validation of frequently visited sites. These optimizations remove most validation-related delays.