TLS Extension Analyzer

Analyze TLS extensions supported by a server

About TLS Extensions

TLS extensions are parameters sent during the TLS handshake that enable additional features and capabilities. They include supported elliptic curves, ALPN (Application-Layer Protocol Negotiation), key share data for TLS 1.3, Server Name Indication (SNI), session tickets, and many others. Analyzing these extensions helps understand server capabilities, troubleshoot compatibility issues, and ensure optimal TLS configuration.

How to Use

Enter the domain name of the server you want to analyze.
Click "Check" to inspect the TLS extensions supported by the server.
Review the results showing supported groups, ALPN protocols, key share, and other extensions.
Use the information to verify TLS configuration and troubleshoot compatibility.

Use Cases

•Verify that a server supports the latest TLS 1.3 extensions
•Troubleshoot compatibility issues between clients and servers
•Check which ALPN protocols (HTTP/2, HTTP/1.1) a server advertises
•Audit supported elliptic curves for forward secrecy compliance

Frequently Asked Questions

TLS extensions are additional parameters that can be included in TLS handshake messages to enable optional features. They were introduced in TLS 1.0 and expanded significantly in TLS 1.3. Common extensions include SNI (server name), ALPN (protocol negotiation), supported_groups (elliptic curves), and key_share.

ALPN (Application-Layer Protocol Negotiation) is a TLS extension that allows the client and server to negotiate which application protocol to use over the TLS connection, such as HTTP/2 or HTTP/1.1. It is essential for modern web performance, as HTTP/2 requires ALPN to function properly.

TLS 1.3 requires the supported_versions extension and uses several mandatory extensions including key_share (for key exchange), signature_algorithms, and supported_groups. The server must also support the extension for pre_shared_key and cookie extensions for session resumption.

Tips & Best Practices

•Analyze TLS extensions to understand client and server capabilities
•Configure important extensions like SNI, ALPN, and OCSP stapling
•Monitor extension usage for security and compatibility analysis
•Compare extension support across different TLS implementations

Technical Details

Extensions: TLS extension identification and analysis
Types: SNI, ALPN, OCSP stapling, session tickets, supported groups
Support: Extension support detection and negotiation
Output: TLS extension list with support and security assessment