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opensslrsadigital-signaturesaml

How to create public and private key with OpenSSL?

My questions are:

  • How to create
    • a public key
    • and a private key with OpenSSL on Windows?
  • How to put the created public key
    • in a .crt file and
    • the private one in a .pkcs8 file?

I want to use these two keys to sign a SAML assertion in Java.

Solution

  • 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