on a build without OpenSSL,

ssh-keygen.exe -t ed25519 -P Bull -f C:\mspctl\openssh\id_ED25519
Generating public/private ed25519 key pair.
Saving key "C:\\mspctl\\openssh\\id_ED25519" failed: invalid argument

This occurs when we compile on windows, but we believe it also repros on other os.

The cause is that when passphrase is not empty, ciphername is assigned to DEFAULT_CIPHERNAME("aes256-cbc") at the following line in function sshkey_private_to_blob2, but "aes256-cbc" is not valid in ciphers array when WITH_OPENSSL is 0

	if (passphrase == NULL || !strlen(passphrase)) {
		ciphername = "none";
		kdfname = "none";
	} else if (ciphername == NULL)
		ciphername = DEFAULT_CIPHERNAME;