RSA, Certificates and Chain of trust

Question 1

what is .pem file extension used for?

Answer 1

pem is extension that is used for files that include certificates. And also we can use that extension for storage of private key.

Question 2

what does the below openssl command do?

openssl genrsa -aes256 -out private.pem

Answer 2

generates a encrypted private key. Encryption is done using aes256 algorithm. This key is saved to a output file name private.pem

Question 3

openssl genrsa -aes256 -out private.pem

In this command that is used to generate a key, we see it is a private key. Where then is the public key?

Answer 3

Public key is also encoded here in private key and we are able to extract it from this private key.

And for that you can use other command.

openssl rsa -in private.pem -outform PEM -pubout -out public.pem

Question 4

what does this command do?

openssl rsa -in private.pem -outform PEM -pubout -out public.pem

Answer 4

this will extract the public key out of the file private.pem, and save it to the file public.pem