Create PKCS#1 formatted RSA key using OpenSSL v3.0.0

Question

I wanted to confirm if we can create PKCS#1/traditional formatted RSA keys using version 3.0.0 of OpenSSL. I guess following command is giving me the output in PKCS#8 format. openssl genrsa -out server.key 2048

Thanks.

Answer 1

Using OpenSSL 3.0, you can use the -traditional switch to get the older format for your output, both for the openssl rsa and openssl genrsa subcommands. Tested on Ubuntu 22.04.

Answer 2

You can do this directly(PKCS#8):

openssl genpkey -out rsakey.pem -algorithm RSA -pkeyopt rsa_keygen_bits:2048
cat rsakey.pem 
-----BEGIN PRIVATE KEY-----
base64_encode xxx
-----END PRIVATE KEY-----

openSSL 1.1.1(PKCS#1)

openssl genrsa -out server.key 2048

cat server.key 

-----BEGIN RSA PRIVATE KEY-----
base64_encode xxx
-----END RSA PRIVATE KEY-----

openssl pkcs8 to pkcs1 command

openssl rsa -in rsakey.pem -out rsakey_pkcs1.pem
cat rsakey_pkcs1.pem
-----BEGIN RSA PRIVATE KEY-----
base64_encode xxx
-----END RSA PRIVATE KEY-----