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What is TLS?

Transport Layer Security. A protocol that encrypts communication, detects tampering and authenticates servers with certificates. HTTPS is HTTP protected by TLS.

Japanese name: TLS

TLS appears in 10 practice questions across 4 topics, including Computer Networking Basics, Web Technology Basics, Information Security Basics.

Field: Computer Networking Basics

Try it: questions about TLS

A client makes a new HTTPS connection (TLS 1.3 over TCP) to a web server with a round-trip time (RTT) of 100 ms. Roughly how long does it take until the response to the first request starts to arrive? Assume DNS resolution is already done, and ignore server processing time and data transfer time.

  1. AAbout 100 ms
  2. BAbout 300 ms
  3. CAbout 200 ms
Show answer and explanation

Answer: B. About 300 ms

First, the TCP three-way handshake takes one round trip (the client can send its first TLS message together with the final ACK). Next, the TLS 1.3 handshake takes one round trip, and then the HTTP request and response take one more, for three round trips in total: 3 × 100 = 300 ms. With TLS 1.2 the key exchange takes two round trips, giving four round trips, or 400 ms. This waiting time depends on the number of RTTs, which is set by distance, so adding link bandwidth does not shorten it. QUIC, used by HTTP/3, combines the transport and cryptographic handshakes into one round trip and also offers a way to send data in the first flight when reconnecting (0-RTT).

Which of the following does HTTPS (HTTP protected by TLS) protect?

  1. AThat the operator of the website you connect to is a trustworthy person or organization without malicious intent
  2. BThat the fact you are communicating, and the IP address of the server you connect to, cannot be seen along the path
  3. CThat the content cannot be read or altered in transit, and that the server you connect to is the legitimate holder of the domain name in its certificate
Show answer and explanation

Answer: C. That the content cannot be read or altered in transit, and that the server you connect to is the legitimate holder of the domain name in its certificate

TLS provides three things: encryption of the communication (confidentiality), detection of tampering (integrity) and authentication of the server. The server presents a certificate, and the browser checks it by following signatures back to a certificate authority (CA) it trusts and confirms that it matches the domain name in the URL. What this proves, however, is only that you are talking to the holder of that domain name; it says nothing about whether the site's operator is honest. Even a scam site can obtain a certificate for its own domain. Also, the IP header is not encrypted, so which IP address you talk to, when and how much can be seen along the path.

TLS in the explanations

Questions that mention TLS (10)

  1. A client makes a new HTTPS connection (TLS 1.3 over TCP) to a web server with a round-trip time (RTT) of 100 ms. Roughly how long does it take until the response to the first request starts to arrive? Assume DNS resolution is already done, and ignore server processing time and data transfer time.
  2. Which of the following does HTTPS (HTTP protected by TLS) protect?
  3. In TLS, why can a browser conclude that the server it connects to is not an impostor?
  4. From a web server with an RTT of 40 ms, one HTML file and the four images it references are fetched one after another. Assume that establishing a TCP connection takes one round trip and each request and response take one round trip, and ignore data transfer time, server processing time, TLS and connection teardown. Which of the following is the difference in total time between opening a new TCP connection for each object and reusing one TCP connection (a persistent connection)?
  5. 1.5 MB of text data is compressed with gzip to one third of its size and sent. The bandwidth is 10 Mbps and the RTT is 100 ms, and before the data starts to be sent, the TCP connection, the TLS handshake and the HTTP request take three round trips in total. Assume 1 MB = 10^6 bytes, and ignore compression and decompression time, headers and waiting caused by TCP congestion control. Which of the following is closest to the time until all the data has been received?
  6. Which correctly describes the basic function of a (packet-filtering) firewall?
  7. Which correctly describes an internet VPN?
  8. Which of the following correctly describes a reverse proxy?
  9. When sending a large file encrypted to someone, which procedure describes the commonly used hybrid encryption scheme?
  10. In a Kubernetes cluster, HTTPS requests arriving for one host name should be routed to the api Service if the path begins with /api, and to the web Service otherwise. Which of the following resources is suitable for defining this routing rule?

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Related terms

HTTP (Hypertext Transfer Protocol) Reverse proxy DNS (Domain Name System) Three-way handshake Public-key cryptography Symmetric-key cryptography Kubernetes Pod ARP CIDR

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