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