Generate Certificate Signing Request (CSR) from private key with passphrase openssl x509 -x509toreq -in example.crt -out example.csr -signkey example.key -passin pass:foobar Generate RSA private key (2048 bit) openssl genrsa -out private.pem 2048 Generate a Certificate Signing Request (CSR) openssl req -sha256 -new -key private.pem -out csr.pem Generate RSA private key (2048 bit) and a Certificate Signing Request (CSR) with a single command openssl req -new -newkey rsa:2048 -nodes -keyout server.key -out server.csr Convert private key to PEM format openssl rsa -in server.key -outform PEM -out server.pem Generate a self-signed certificate that is valid for a year with sha256 hash openssl x509 -req -sha256 -days 365 -in csr.pem -signkey private.pem -out certificate.pem View details of a RSA private key openssl rsa -in private.pem -text -noout View details of a CSR openssl req -in csr.pem -text -noout View details of a Certificate openssl x509 -in certificate.pem -text -noout View details of a Certificate in DER format openssl x509 -inform der -in certificate.cer -text -noout Convert a DER file (.crt .cer .der) to PEM openssl x509 -inform der -in certificate.cer -out certificate.pem Convert a PEM file to DER openssl x509 -outform der -in certificate.pem -out certificate.cer

https://www.digitalocean.com/community/tutorials/openssl-essentials-working-with-ssl-certificates-private-keys-and-csrs

https://help.interfaceware.com/v6/how-to-create-self-certified-ssl-certificate-and-publicprivate-key-files

There is no .key format. You can have private (or public) key in PEM or DER encoding. And you can have private key in PKCS#1 or PKCS#8 format. The extensions (.der, .pem, .key, .cer etc.) are only for convenience to easily identify what is inside (well, we wish to trust that the content corresponds to the extension used).

Command openssl genrsa -out rsaprivkey.pem 1024 generated private key in PKCS#1 format and PEM encoding. In the guide you mentioned there are additional steps to take:

openssl rsa -in rsaprivkey.pem -pubout -outform DER -out rsapubkey.der openssl pkcs8 -topk8 -inform PEM -outform DER -in rsaprivkey.pem -out rsaprivkey.der -nocrypt

Step 1 extracts the public key from rsaprivkey.pem and encodes it in DER format. Step 2 transforms the private key from PKCS#1 to PKCS#8 format (unencrypted) and DER encoding.

The guide also mentions that some Java SSO example expects DSA keys. The keys that you generated using openssl genrsa -out rsaprivkey.pem 1024 are RSA keys.

https://www.namecheap.com/support/knowledgebase/article.aspx/9834/69/how-can-i-find-the-private-key-for-my-ssl-certificate/

https://dynacont.net/documentation/linux/openssl/

https://www.ssl.com/how-to/export-certificates-private-key-from-pkcs12-file-with-openssl/

https://wiki.segger.com/HOWTO_convert_PEM_certificates_and_keys_to_DER_format_for_emSSL

https://techdocs.broadcom.com/us/en/ca-enterprise-software/it-operations-management/unified-infrastructure-management/20-3/upgrading/ca-uim-upgrade-step-3-deploy-the-upgrade/upgrade-uim-server/secure-hub-and-robot-ca-uim-9-sp1/Convert-Files-to--pem-Format.html

https://superuser.com/questions/1644533/how-do-i-use-the-openssl-command-to-decode-a-public-key-pem-file

https://blog.ndpar.com/2017/04/17/p1-p8/

https://www.mailhardener.com/kb/how-to-create-a-dkim-record-with-openssl

http://lunar.lyris.com/help/Content/generating_public_and_private_keys.html

https://www.misterpki.com/pkcs8/

https://help.internetx.com/display/SSLEN/OpenSSL+-+Most+Common+Commands

https://www.thedigitalcatonline.com/blog/2018/04/25/rsa-keys/