Using the git version of ssh-audit, curve25519-sha256 is currently flagged as an unknown algorithm whereas curve25519-sha256@libssh.org is correctly identified.
Looking at the sshd_config man page for OpenSSH 7.6p1, both are valid for KexAlgorithms. The default sequence is listed as
curve25519-sha256,curve25519-sha256@libssh.org,
ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
diffie-hellman-group-exchange-sha256,
diffie-hellman-group14-sha1
Some software such as SecureCRT 8.5.2 require the usage of curve25519-sha256 instead of curve25519-sha256@libssh.org
Using the git version of ssh-audit, curve25519-sha256 is currently flagged as an unknown algorithm whereas curve25519-sha256@libssh.org is correctly identified.
Looking at the sshd_config man page for OpenSSH 7.6p1, both are valid for KexAlgorithms. The default sequence is listed as
Some software such as SecureCRT 8.5.2 require the usage of curve25519-sha256 instead of curve25519-sha256@libssh.org