Generating SSL key pair

You can generate a public-private keypair with the genrsa context (the last number is the keylength in bits):

openssl genrsa -out keypair.pem 2048

To extract the public part, use the rsa context:

openssl rsa -in keypair.pem -pubout -out publickey.crt

Finally, convert the original keypair to PKCS#8 format with the pkcs8 context:

openssl pkcs8 -topk8 -inform PEM -outform PEM -nocrypt -in keypair.pem -out pkcs8.key

Source: http://stackoverflow.com/questions/44474516/