openssl: How to check that a certificate matches a private key

2 min read

If we try to install a certificate on a service but we install an incorrect private key, the service will fail, most likely, with some cryptic message. But, how do we make sure that a certificate has been generated using the correct private key? Checking the modulus of each one can help verifying this

13/07/2021

Test SSL protocols availability using openssl s_client

3 min read

To make sure we don't publish an SSL service with vulnerable protocols enabled we can check which protocols the server has enabled using openssl s_client

Depending on the OpenSSL version we have we will have different procotols available. For example, if we are using OpenSSL 1.0.2j we will have the following options for s_client:

 -ssl2 - just use SSLv2 -ssl3 - just use SSLv3 -tls1_2 - just use TLSv1.2 -tls1_1 - just use TLSv1.1 -tls1 - just use TLSv1 -dtls1 - just use DTLSv1 

On the other hand, if we are using OpenSSL 1.1.1f we will only have:

 -tls1 Just use TLSv1 -tls1_1 Just use TLSv1.1 -tls1_2 Just use TLSv1.2 -tls1_3 Just use TLSv1.3 

06/07/2021

How to generate a self-signed certificate using OpenSSL

2 min read

Using openssl we can create a self-signed using a non interactive command suitable for automation if we give all the information at once such as the CN, and the days to expire

21/05/2021