63 lines
2.7 KiB
Markdown
63 lines
2.7 KiB
Markdown
---
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tags: [world-wide-web, internet, encryption, server-management]
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created: Friday, December 14, 2024
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---
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# HTTPS
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The problem with standard, unencrypted HTTP requests is that the data can be
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captured in transit and be observed or modified by malicious actors.
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HTTPS is the solution. It encrypts the entirety of the HTTP request and response
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(URL, headers, body).
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It utilises two types of encryption to send messages securely:
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- symmetric encryption
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- a single shared key between client and server to encrypt the messages sent
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between them
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- asymmetric encryption
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- two keys are used: a [public key](./bbdcb54f_public_key_cryptography.md) to
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encrypt the data and a private key to decrypt it. The public key can be
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shared freely so anyone can encrypt and send data to a peer but only the
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peer can receive and decrypt it
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> Symmetric encryption applies once the server has been authenticated and its
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> public key has been shared with the client. Asymmetric encryption applies at
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> the initiation phase only.
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The encryption protocol used is TLS - the **Transport Layer Security Protocol**.
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Previously SSL (Secure Sockets Layer) was used but has been deprecated over
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security concerns.
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The initial handshake process takes place entirely within the Network Layer,
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over TCP. Only once encryption is secured is HTTPS activated at the
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[Application Layer](./Application_Layer_of_Internet_Protocol.md)
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## How communication over HTTPs works
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- An initial handshake is shared between client and server, agreeing that
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communication will be encrypted. This is public. "Client hello" and "Server
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hello". Some random numbers are exchanged at this point
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- The server sends a digital [certificate](./Certificate_authorities.md) key The
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client checks that the certificate is valid
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- If valid, the client encrypts a string of bytes using the public key and sends
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it to the server. This is called the "premaster secret"
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- This is decrypted by the server
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- The premaster secret, along with the random bytes from the handshake is then
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used to compute a shared secret key (symmetric) which is used to encrypt all
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subsequent messages for the duration of the session
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## Caching
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Once symmetric exchange is achieved the TLS handshake is complete and lasts
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typically until either terminates it.
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However, some caching does occur on both the server and browser side. Both use
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session IDs to enact an abbreviated handshake such as when the session cache
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expires. This way, certificate validation and the asymmetric exchange can be
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skipped. These tickets are shared as part of the original exchange and the
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client can present them to the server as proof they already authenticated when
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they come back later.
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