So for example: let privateKey = Curve25519.Signing.PrivateKey() let publicKey = privateKey.publicKey What I want is the string representation of the private key and public key shown. I can get a base64 String: privateKey.rawRepresentation.base64EncodedString() But when I try to get the String of the private key with utf8 encoding, I get nil: String(data: privateKey.rawRepresentation, encoding: .utf8) // this gives back nil

It's very common for signing keys of any type to have a String representation, so I would expect there is one for any ed25519 key pair. There are a number of examples online, and you can see a String representation through generating them in OpenSSH ssh-keygen -t 25519

Posting a command that I cannot run without installing software is not particularly helpful. I stated in the opening, and that post, that I used OpenSSH which is what the command is from (and I stated the command as well). And I've never had to install it so I assumed it comes pre-loaded in a macbook. Ah, I think you meant ssh-keygen -t ed25519. So, for example: Yes, I forgot the "ed" in that command. That's my mistake. And yes, that representation is what I'm having trouble with adding to Curve25519. My main objective of adding external keys has been completed. While I couldn't do it with the OpenSSH generated keys, I had to decode my acquired keys from a different encoding and made those decoded keys into byte arrays to insert.