TLS and HTTPS - University of Washington

TLS and HTTPS CSE 461 Section A joke about bad weather TLS Fundamentals Transport Layer Security protocol Standard protocol for encrypting Internet traffic Previously known as SSL (Secure Sockets Layer), which has been around since 1994 TLS replaced SSL in 1999

Used for HTTPS (HTTP Secure) traffic Supported by nearly every web browser Purposes for TLS (1) When we dont use TLS, web traffic goes over unencrypted This includes HTTP payloads, but also HTTP headers Why are headers a problem too?

Purposes for TLS (2) Data integrity Server (and client) authentication Defcon Wall of Sheep TLS and CONNECT HTTP CONNECT is used to establish a two- way connection tunnel between two parties After this, a triple handshake is performed over the tunnel After the handshake, the two

parties can communicate securely Well take a closer look at this handshake TLS Handshake Protocol (Concept) What do we need to do to communicate securely? Make sure were speaking the same language Prove who we are Establish a secret code

TLS Handshake Protocol (Rough Details) Client tells the server its protocol version and what cryptographic algorithms it can use Server responds with a protocol version and cryptographic algorithm to use Server sends its certificate to verify its identity Client verifies certificate and sends Pre-Master Secret, encrypted so only the server can read it Client and server both use that PMS to generate a Master Secret, which is used to generate encryption keys

Communication commences Heartbleed bug 2014 Bug in OpenSSL implementation of TLS Clients ask for a heartbeat message to test and keep alive communication links In OpenSSL, length checking wasnt properly performed on the heartbeat data TLS Exploits How might data be intercepted by a MITM,

even when encrypted over TLS? Implementation bugs (e.g., Heartbleed, 3Shake) Server/browser attacks (e.g., truncation attack) Truncate logout packet from user Users browser tells them theyve logged out They havent Side-channel attacks Side-channel TLS Attacks (1)

Some data is leaked even with encryption Packet send timing Payload size AJAX interfaces that load content dynamically provide insight into what the user is typing Side-channel TLS Attacks (2) Autocomplete Packet Sizes for "hackers" 780

760 Size in Bytes 740 720 Trial 1 Trial 2 Trial 3 700

680 660 640 1 2 3 4 Letter Number

5 6 7 Autocomplete Packet Sizes for "benaloh" 750 740 730

Size in Bytes 720 710 700 Trial 1 Trial 2 Trial 3 690 680 670

660 650 1 2 3 4 Letter Number 5

6 7 Autocomplete Packet Sizes for "xvwqxzx" 800 700 600 Size in Bytes

500 400 Trial 1 Trial 2 Trial 3 300 200

100 0 1 2 3 4 Letter Number 5

6 7 Questions?

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