These commands allow you to convert certificates and keys to different formats to make them compatible with specific types of servers or software. openssl s_client \ -connect smtp.gmail.com:587 \ -starttls smtp For this, after connect I submit necessary commands with username and password in base64: EHLO smtp.gmail.com AUTH LOGIN MAIL FROM: RCPT TO: <*****@gmail.com> DATA Subject: Sending an email using telnet Hello, This is an email sent by using the telnet command. s_client can be used to debug SSL servers. If the connection succeeds then an HTTP command can be given such as GET / to retrieve a web page. The command below makes life even easier as it will automatically delete everything except the PEM certificate. openssl s_client -connect linuxadminonline.com:443 -showcerts. Below example shows on how to connect domain using TLS 1.2 protocol. Verification could be done using s_client command in openssl. HTTP/1.0 400 Bad Request Content-Length: 0 The -ign_eof keeps the connection open to … Below, I used a GET withHTTP/1.0 and tweeter rudely refused my request:. Here is a list of the most common s_client command’s variations: To test http SSL connection type: openssl s_client -connect www.sslshopper.com:443 -CApath /etc/ssl/certs/ If the connection succeeds then an HTTP command can be given such as ``GET /'' to retrieve a web page. To connect to an SSL HTTP server the command: openssl s_client -connect servername:443 would typically be used (https uses port 443). The above command will help you to see the contents of the PKCS12 file. Does anyone know how to use s_client of openssl to send a short string to the server? You can echo it in. openssl s_client -connect linuxadminonline.com:443 -tls1_2 openssl s_client -connect www.paypal.com:443; Converting Using OpenSSL. openssl s_client -connect www.somesite.com:443 > cert.pem Now edit the cert.pem file and delete everything except the PEM certificate. s_client can be used to debug SSL servers. Convert PKCS12 format to PEM certificate openssl pkcs12 –in cert.p12 –out cert.pem. Have a look: OpenSSL Command to Generate Private Key openssl genrsa -out yourdomain.key 2048 OpenSSL Command to Check your Private Key openssl rsa -in privateKey.key -check OpenSSL Command to Generate CSR. As an example we will use www.sslshopper.com, test.rebex.net and gmail.com. If the connection succeeds then an HTTP command can be given such as "GET /" to retrieve a web page. The basic command outline is as follows: [root@host ~]# openssl s_client -connect : In order to test a connection, we are going to need a domain name and a port. In OpenSSL 1.0.2 and newer, when you connect to a server, the s_client command prints the strength of the ephemeral Diffie-Hellman key if one is used. If you wish to use existing pkcs12 format with Apache or just in pem format, this will be useful. Connect SSL using TLS 1.2 only While using openssl command one can mention the specific protocol using which you can connect to the domain over SSL. To connect to an SSL HTTP server the command: openssl s_client -connect servername:443 would typically be used (https uses port 443). Thus, to determine the strength of some server’s DH parameters, all you need to do is connect to it while offering only suites that use the DH key exchange. Among the many commands that OpenSSL offers, for testing secure connections we will use the openssl s_client command. If you have generated Private Key: To connect to an SSL HTTP server the command: openssl s_client -connect servername:443 would typically be used (https uses port 443). 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