Скачать или смотреть Understanding Cipher Suites: How They Are Determined and Changed in TLS Applications

Dive deep into the concept of cipher suites in TLS applications. Learn what factors determine the cipher suite selection and how to switch to your preferred choice.
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Introduction to Cipher Suites in TLS

When building a secure application using Transport Layer Security (TLS), one critical element you must understand is the cipher suite. A cipher suite is a collection of algorithms that help secure network connections through encryption, authentication, and integrity checks.

If you're using a library like mbedtls in your TLS application, you might have noticed some messages during debugging that specify the selected cipher suite. For instance, selected ciphersuite: TLS-ECDHE-RSA-WITH-CHACHA20-POLY1305-SHA256 indicates which algorithms are currently in use.

This leads us to a common question: What determines the choice of a cipher suite, and how can you change it?

What Determines the Cipher Suite?

Understanding what influences the selection of a cipher suite is fundamental to configuring your application for optimal security. The factors that play a role in determining the cipher suite include:

Supported Ciphers: The server and client both maintain a list of supported cipher suites. The intersection between these two lists will determine the cipher suite used for that session.

Client Preferences: Often, the client (the party initiating the connection) will have preferences regarding which cipher suites it wants to use, impacting the ultimate selection.

Server Configuration: The server may also have specific configurations that dictate which cipher suites it prefers, possibly affecting the final choice if both parties support the same algorithms.

Quality of Security: In many cases, more secure ciphers are preferred over less secure options based on recommendations from security bodies or internal policies.

TLS Stack: The specific version of the TLS protocol in use (like TLS 1.2 or TLS 1.3) can also influence the available cipher suites.

Why Was CHACHA20-POLY1305 Chosen?

In the example you provided, the chosen cipher suite includes CHACHA20-POLY1305. This selection indicates:

The server is capable of using the ChaCha20 stream cipher, which is often preferred for performance on mobile devices and by browsers when the hardware acceleration for AES is unavailable.

The choice of cipher could also hint at a preference for modern, secure ciphers over older algorithms.

Ultimately, since the selection of a cipher suite is a negotiation between the client and server, it highlights the importance of both parties' capabilities and configurations.

Changing Your Cipher Suite

If you're looking to change the cipher suite to TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256, there are a few important pieces to consider:

Certificate Type:

The currently chosen cipher suite (TLS-ECDHE-RSA-WITH-CHACHA20-POLY1305) uses an RSA certificate for authentication.

The desired cipher suite uses an ECDSA (Elliptic Curve Digital Signature Algorithm) certificate. Thus, you cannot switch to this desired cipher suite without ensuring that the server has an ECDSA certificate available.

Server Capabilities:

Make sure your server is configured to support ECDSA certificates. Some servers can handle both RSA and ECDSA, but the actual choice of certificate may still depend on configuration settings.

Client and Server Configuration:

Ensure both the client and the server are set to prioritize and support the new cipher suite. This may involve altering configuration files or client arguments to include this suite in their list of supported ciphers.

Conclusion

Navigating the world of cipher suites can initially seem daunting, but understanding the influences that determine their selection and how to configure them properly can greatly enhance the security of your TLS applications.

By knowing how to switch cipher suites, you can ensure that your data remains encrypted an