While most examples we find test port 443, this will work with other ports as well. The returned list of certificates by the server when using the showcerts flag is not a verified chain and is returned in the same order the server sent them. Other than that one difference, the output is the same. The showcerts flag appended onto the openssl s_client connect command prints out and will show the entire certificate chain in PEM format, whereas leaving off showcerts only prints out and shows the end entity certificate in PEM format. Openssl s_client -connect :443 -showcerts Openssl s_client -connect :443 -tlsextdebugĪdditional information is included and can be used to verify the ssl configuration of the server. To debug the SSL/TLS connection with openssl s_client connect, append the -tlsextdebug flag onto our command: If the specified protocol is not supported on the server, we will receive an error similar to: “SSL routines:tls_construct_client_hello:no protocols available“ To verify the protocol, view the SSL-Session section of the console output. Openssl s_client -connect :443 -no_tls1_3 To disable TLSv1.3, use the -no_tls1_3 flag: Alternatively, to disable the use of a specific SSL/TLS protocol version, the following flags are supported: -no_ssl2, -no_ssl3, -no_tls1, -no_tls1_1, -no_tls1_2, and -no_tls1_3.įor the case of, TLSv1.3 is supported. Other supported SSL and TLS version flags include -tls1_2, tls1_1, tls1, ssl2, and ssl3. For example, to test TLS 1.3 with openssl s_client, run the following: To specify the TLS version in the connection for testing various protocols, add the appropriate TLS/SSL flag to the command. The server’s public key bit length is also returned. The end entity server certificate will be the only certificate printed in PEM format.ĭetails about the SSL handshake, its verification, and the TLS version and cipher will be returned. The information will include the server’s certificate chain, printed as subject and issuer. Use the openssl s_client -connect flag to display diagnostic information about the SSL connection to the server. This post covers various examples of testing SSL connections with different ciphers, TLS versions, and SSL server certificate analysis. The OpenSSL s_client command is a helpful test client for troubleshooting remote SSL or TLS connections.
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