openssl - generate DER format

# generate private key
openssl genrsa -out myprivate.key

 

# extract the public key from the private key

openssl rsa -in myprivate.key -pubout -out mypublic.key

 

# conver the private key to DER format

openssl rsa -in myprivate.key -out myprivate.key.der -outform der

 

# convert the public key to DER format

openssl rsa -in mypublic.key -out mypublic.key.der -pubin -outform der